BlogJava-杂家-随笔分类-3.Hibernate

Hibernate连接池

淘声依旧 — Tue, 03 Mar 2009 09:16:00 GMT

我花了三个晚上的时间，把hibernate与三种常用连接池的配置研究出来，希望对大家有帮助。

以下三种连接都是以连接MySQl为例。

root
8888

上面的一段配置，在c3p0和dbcp中，都是必需的，因为hibernate会根据上述的配置来生成connections，再交给c3p0或dbcp管理.但是，proxool则不能，虽然说服文档上说proxool也可以和hibernate结合,但我按照官方文档上的说明怎么配也出错，而且，到了 sun和hibernat有的官方网站上问了几天，都没有一个人回复。后来我只能让proxool自身来生成连接，这在下面再讲。

1 C3P0

只需在hibernate.cfg.xml中加入
5
30
1800
50

还有在classespath中加入c3p0-0.8.4.5.jar

2 dbcp

在hibernate.cfg.xml中加入

100
1
60000
10

100
1
60000
10

还有在classespath中加入commons-pool-1.2.jar 和commons-dbcp-1.2.1.jar.

3 proxool

在hibernate.cfg.xml中加入

pool1
ProxoolConf.xml
net.sf.hibernate.connection.ProxoolConnectionProvider

然后，在和hibernate.cfg.xml同一个目录下，加一个ProxoolConf.xml文件，内容为

pool1

jdbc:mysql://localhost:3306/struts?useUnicode=true&characterEncoding=GBK

org.gjt.mm.mysql.Driver

90000

100

并在classespath中加入proxool-0.8.3.jar

结论：

由于在hibernate3.0中，已经不再支持dbcp了，hibernate的作者在hibernate.org中，明确指出在实践中发现dbcp 有 BUG,在某些种情会产生很多空连接不能释放，所以抛弃了对dbcp的支持。我不知是否在dbcp最新版本中解决了这个问题，我以前在一个访问量不大的项目中用过dbcp，运行了一年多都没出现问题。不过在网上的确也有不少网友指出dbcp在大型的应用中会出现不稳定的情况。所以在真相未经证实的情况下，我觉得对dbcp持慎重的态度。

至于c3p0，有评论说它的算法不是最优的，而且，我在matrix中，见到有网友做了一个实验，在同一项目中分别用了几个常用的连接池，然后测试其性能，发现c3p0占用资源比较大，效率也不高。

所以，基于上述原因，我才花两晚的时间去研究proxool的配置，proxool不少行家推荐使用，而且暂时来说，是负面评价是最少的一个。在三星中也有项目是用proxool的。

欢迎大家就连接池的问题多研究，多多发表自己的经验心得。

淘声依旧 2009-03-03 17:16 发表评论

使用Hibernate3实现分页功能

淘声依旧 — Wed, 29 Oct 2008 11:45:00 GMT

参考资料:

http://blog.csdn.net/zhjb1025/archive/2006/04/19/668631.aspx

http://www.cnblogs.com/HuaiHuai/archive/2005/08/09/211062.html

整理的代码如下：

Page.java接口

package org.domain.scrm4u.helper;

import java.util.List;

public interface Page {

    boolean isFirstPage();

    boolean isLastPage();

    boolean hasNextPage();

    boolean hasPreviousPage();

    int getLastPageNumber();

    List getThisPageElements();

    int getTotalNumberOfElements();

    int getThisPageFirstElementNumber();

    int getThisPageLastElementNumber();

    int getNextPageNumber();

    int getPreviousPageNumber();

    int getPageSize();

    int getPageNumber();
}

ListPage.java实现：

package org.domain.scrm4u.helper.impl;

import java.util.List;

import org.domain.scrm4u.helper.Page;

public class ListPage implements Page {

    private List elements;
    private int pageSize;
    private int pageNumber;

    public ListPage(List elements, int pageNumber, int pageSize) {
        
        this.elements = elements;
        this.pageSize = pageSize;
        this.pageNumber = pageNumber;
        if (Integer.MAX_VALUE == this.pageNumber) this.pageNumber = (getTotalNumberOfElements() / this.pageSize);
    }

    public boolean isFirstPage() {
        
        return getPageNumber() == 0;
    }

    public boolean isLastPage() {
        
        return getPageNumber() >= getLastPageNumber();
    }

    public boolean hasNextPage() {
        
        return ((getPageNumber() + 1) * getPageSize()) < (getTotalNumberOfElements() + 1);
    }

    public boolean hasPreviousPage() {
        
        return getPageNumber() > 0;
    }

    public int getLastPageNumber() {

        double totalResults = new Integer(getTotalNumberOfElements()).doubleValue();
        return new Double(Math.floor(totalResults / getPageSize())).intValue();
    }

    public List getThisPageElements() {

        final int start = getPageNumber() * getPageSize();
        return elements.subList(
                    Math.min(start, getTotalNumberOfElements() + 1), 
                    Math.min(start + getPageSize(), getTotalNumberOfElements() + 1)
               );
    }

    public int getTotalNumberOfElements() {
        return elements.size() - 1;
    }

    public int getThisPageFirstElementNumber() {
        return getPageNumber() * getPageSize() + 1;
    }

    public int getThisPageLastElementNumber() {
        int fullPage = getThisPageFirstElementNumber() + getPageSize() - 1;
        return getTotalNumberOfElements() < fullPage ? getTotalNumberOfElements() : fullPage;
    }

    public int getNextPageNumber() {
        return getPageNumber() + 1;
    }

    public int getPreviousPageNumber() {
        return getPageNumber() - 1;
    }

    public int getPageSize() {
        return pageSize;
    }

    public int getPageNumber() {
        return pageNumber;
    }
}

HibernatePage.java实现：

package org.domain.scrm4u.helper.impl;

import java.util.List;

import org.domain.scrm4u.helper.Page;
import org.hibernate.HibernateException;
import org.hibernate.Query;
import org.hibernate.ScrollMode;
import org.hibernate.ScrollableResults;

public class HibernatePage implements Page {

    protected List elements;
    protected int pageSize;
    protected int pageNumber;
    protected int totalElements = 0;

    private ScrollableResults scrollableResults;

    private HibernatePage(int pageNumber, int pageSize) {
        
        this.pageNumber = pageNumber;
        this.pageSize = pageSize;
    }

    public boolean isFirstPage() {
        return getPageNumber() == 0;
    }

    public boolean isLastPage() {
        
        return getPageNumber() >= getLastPageNumber();
    }

    public boolean hasNextPage() {
        
        return elements.size() > getPageSize();
    }

    public boolean hasPreviousPage() {
        
        return getPageNumber() > 0;
    }

    public int getLastPageNumber() {

        double totalResults = new Integer(getTotalNumberOfElements()).doubleValue();
        return new Double(Math.floor(totalResults / getPageSize())).intValue();
    }

    public List getThisPageElements() {

        return hasNextPage() ? elements.subList(0, getPageSize()) : elements;
    }

    public int getTotalNumberOfElements() {
        
        return totalElements;
    }

    public int getThisPageFirstElementNumber() {
        
        return getPageNumber() * getPageSize() + 1;
    }

    public int getThisPageLastElementNumber() {
        
        int fullPage = getThisPageFirstElementNumber() + getPageSize() - 1;
        return getTotalNumberOfElements() < fullPage ? getTotalNumberOfElements() : fullPage;
    }

    public int getNextPageNumber() {
        
        return getPageNumber() + 1;
    }

    public int getPreviousPageNumber() {
        
        return getPageNumber() - 1;
    }

    public int getPageSize() {
        
        return pageSize;
    }

    public int getPageNumber() {
        
        return pageNumber;
    }

    public static HibernatePage getScrollPage(Query query, int pageNumber, int pageSize, ScrollMode scrollMode) {
        
        HibernatePage sp = new HibernatePage(pageNumber, pageSize);
        try {
            sp.scrollableResults = query.scroll(scrollMode);
            if(scrollMode == ScrollMode.SCROLL_SENSITIVE){
                sp.scrollableResults.last();
                sp.totalElements = sp.scrollableResults.getRowNumber();
            } else {
                sp.totalElements = sp.calculateTotalElementsByList(query);
            }
            sp.determineElements(query);
        } catch (HibernateException e) {
            e.printStackTrace();
        }
        return sp;
    }

    private void determineElements(Query query) throws HibernateException {

        if (Integer.MAX_VALUE == this.pageNumber) this.pageNumber = (getTotalNumberOfElements() / this.pageSize);
        elements = query.setFirstResult(this.pageNumber * this.pageSize).setMaxResults(this.pageSize + 1).list();
    }

    private int calculateTotalElementsByList(Query query) throws HibernateException {
        
        return query.list().size();
    }
}

简单分析一下：

ListPage实现需要把查询的结果集全部取出来。

我们着重还是分析一下HibernatePage的实现。

测试代码如下：

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;


    
import org.hibernate.Query;
import org.hibernate.ScrollMode;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.AnnotationConfiguration;
import org.hibernate.cfg.Configuration;


    
import org.domain.scrm4u.helper.Page;
import org.domain.scrm4u.helper.impl.HibernatePage;
import org.domain.scrm4u.entity.TPsn;


    
public class BusinessService {


    
    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config =  new AnnotationConfiguration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        
        Session session = sessionFactory.openSession();


    
        String Hql = "from TPsn";
        Query query = session.createQuery(Hql);
        
        Page page = HibernatePage.getScrollPage(query, 0, 10, ScrollMode.SCROLL_SENSITIVE);
        List list = page.getThisPageElements();
        for (int i = 0; i < list.size(); i++) {
            TPsn psn = (TPsn)list.get(i);
            System.out.println(psn.getPsnNo() + "\t" + psn.getPsnPnm() + "\t" + psn.getPsnBrthDt());
        }  
        
        session.close();
        sessionFactory.close();
    }
}

测试中发现：

使用ScrollMode.SCROLL_SENSITIVE比ScrollMode.FORWARD_ONLY在性能上要快很多。具体选择要看使用的JDBC驱动是否支撑了，支持scroll的话就可以使用ScrollableResults类来处理结果集了。

当然，我们还可以配合缓存技术让翻页更有效率。

淘声依旧 2008-10-29 19:45 发表评论

hibernate3学习笔记(二十三)｜进阶特性

淘声依旧 — Wed, 29 Oct 2008 11:43:00 GMT

1.悲观锁定：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3608

2.乐观锁定：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3609

3.Lifecycle 介面、Validatable 介面：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3610

4.Interceptor 介面：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3611

5.从映射文件生成数据表：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3612

6.从数据表生成映射文件

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=3613

7.关于Hibernate2的使用资料：

http://www.javaworld.com.tw/confluence/pages/viewpage.action?pageId=833

淘声依旧 2008-10-29 19:43 发表评论

hibernate3学习笔记(二十一)｜二级缓存

淘声依旧 — Wed, 29 Oct 2008 11:42:00 GMT

二级缓存及外部缓存，它能够越过数个Session，通过同一个SessionFactory进行管理和维护。

要使用二级缓存，首先需要对hibernate.cfg.xml文件进行修改：

xml version="1.0" encoding="utf-8"?> 
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
    
<hibernate-configuration> 

    <session-factory> 

        ....
        <property name="hibernate.cache.provider_class">
            org.hibernate.cache.HashtableCacheProvider
        property>
        ....
        
    session-factory> 

hibernate-configuration>

HashtableCache是Hibernate自己所提供的二级缓存的实现，但是由于其性能和功能有限，一般只用于开发和测试。

当然我们可以使用第三方的实现，譬如：org.hibernate.cache.EhCacheProvider，这个需要ehcathe.jar包。

修改User.hbm.xml文件：

xml version="1.0" encoding="utf-8"?>
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_21.model.User" table="user">
    
        <cache usage="read-write"/>
    
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 

        <property name="name" column="name" type="java.lang.String"/> 
        
        <many-to-one name="room" 
                     column="room_id" 
                     class="com.hb3.pack_21.model.Room"
                     cascade="save-update"
                     outer-join="true"/> 
        
    class> 

hibernate-mapping>

这里追加的策略有read-only、read-write、nonstrict-read-write以及transactional。不同的第三方缓存实现所支持的种类是不同的，请参阅：http://www.hibernate.org/hib_docs/v3/reference/en/html/performance.html#performance-cache

在工程的classpath下追加ehcache.xml文件，内容为：

<ehcache>

   <diskStore path="java.io.tmpdir"/>

   <defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="true"
        />
        
ehcache>

测试代码如下：

package com.hb3.pack_21;

import java.io.IOException;
import java.sql.SQLException;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_21.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        User user1 = (User) session.load(User.class, new Integer(1));
        user1.getName();
        
        session.close();
        session = sessionFactory.openSession();
        
        User user2 = (User) session.load(User.class, new Integer(1));
        user2.getName();

        session.close();
        sessionFactory.close();
    }
}

如果不使用二级缓存机制，生成的SQL文为：

Hibernate:
select user0_.id as id0_, user0_.name as name0_0_, user0_.age as age0_0_
from user user0_ where user0_.id=?
Hibernate:
select user0_.id as id0_, user0_.name as name0_0_, user0_.age as age0_0_
from user user0_ where user0_.id=?

使用后，第二级做相同的查询会从二级缓存中读取。

当然，如果打算从二级缓存中清空对象的缓存信息，可以使用SessionFactory的evict()方法，如：

sessionFactory.evict(User.class, user.getId());

淘声依旧 2008-10-29 19:42 发表评论

hibernate3学习笔记(二十二)｜Query缓存机制

淘声依旧 — Wed, 29 Oct 2008 11:42:00 GMT

测试代码如下：

package com.hb3.pack_22;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_22.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        String hql = "from com.hb3.pack_22.model.User";
        
        Query query = session.createQuery(hql);
        List users = query.list();
                
        for(int i = 0; i < users.size(); i++) {
            User user = (User) users.get(i);
            System.out.println(user.getName());
        }
                
        query = session.createQuery(hql);
        users = query.list();
                
        for(int i = 0; i < users.size(); i++) {
            User user = (User) users.get(i);
            System.out.println(user.getName());
        }

        session.close();
        sessionFactory.close();
    }
}

执行的结果为：

Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.room_id as room3_0_ from user user0_
chenyan
shenbin
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.room_id as room3_0_ from user user0_
chenyan
shenbin

可见，没有启用Query的快取功能。

如果打算打开Query的快取功能，首先在hibernate.cfg.xml中设定hibernate.cache.use_query_cache属性：

xml version="1.0" encoding="utf-8"?> 
    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
    
<hibernate-configuration> 

    <session-factory> 
        .... 

        <property name="hibernate.cache.use_query_cache">trueproperty> 
        ....
        
    session-factory> 

hibernate-configuration>

然后在每次简历Query时，执行setCacheable(true)：

package com.hb3.pack_22;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;

import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_22.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        String hql = "from com.hb3.pack_22.model.User";
        
        Query query = session.createQuery(hql);
        //使用Query快取 
        query.setCacheable(true);
        List users = query.list();
                
        for(int i = 0; i < users.size(); i++) {
            User user = (User) users.get(i);
            System.out.println(user.getName());
        }
                
        query = session.createQuery(hql);
        //使用Query快取 
        query.setCacheable(true);
        users = query.list();
                
        for(int i = 0; i < users.size(); i++) {
            User user = (User) users.get(i);
            System.out.println(user.getName());
        }

        session.close();
        sessionFactory.close();
    }
}

执行结果为：

Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.room_id as room3_0_ from user user0_
chenyan
shenbin
chenyan
shenbin

其实，Hibernate在启用Query的缓存机制后，会保留执行过的查询SQL和查询结果，在下次查询后会看看SQL是否相同，并看看对应的资料库表格是否有变动(Update/Delete/Insert),如果SQL相同且且资料库也没有变动则将缓存中的结果直接返回。

值得一提的是，Query上有list()与iterator()2个方法用于结果集返回。他们的区别是，list()方法在读取数据库时不会使用缓存机制而直接向数据库发起查询，而iterator()则会将读取到的结果写到缓存中，以便于读取时再次利用。

Session session = sessionFactory.openSession();
        
Query query = session.createQuery("from User");
List users = query.list();
users = query.list();

session.close();

执行结果：

Hibernate: select user0_.id as id, user0_.name as name0_, user0_.age as age0_ from user user0_
Hibernate: select user0_.id as id, user0_.name as name0_, user0_.age as age0_ from user user0_

Session session = sessionFactory.openSession();

Query query = session.createQuery("from User");
Iterator users = query.iterate();
users = query.iterate();

session.close();

执行结果：

Hibernate: select user0_.id as col_0_0_ from user user0_

由于使用iterator()方法时会使用到Session level缓存，所以在查询大量记录时会好用大量的记忆体。必要时可以使用Session的evict()或clear()方法来清除缓存。

请参阅：http://blogger.org.cn/blog/more.asp?name=NaddyLee&id=31540

请注意，尽管iterator()方法时会使用到Session level缓存,但这不能就说在任何情况下都是最有效率的做法。

请看下面的测试：

package com.hb3.pack_22;


    
import java.io.IOException;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.List;


    
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_22.model.User;


    
public class BusinessService {


    
    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();


    
        
        String hql = "from com.hb3.pack_22.model.User";
        
        Query query = session.createQuery(hql);
        
//        List list = query.list(); 
//        Iterator iterator = list.iterator(); 
//        while (iterator.hasNext()) { 
//          User user = (User)iterator.next(); 
//          System.out.println(user.getRoom().getAddress()); 
//      } 
//        System.out.println("====================================="); 
//        list = query.list(); 
//        iterator = list.iterator(); 
//        while (iterator.hasNext()) { 
//          User user = (User)iterator.next(); 
//          System.out.println(user.getRoom().getAddress()); 
//      } 
//         
//        System.out.println("++++++++++++++++++++++++++++++++++++++"); 
        
        query = session.createQuery(hql);
        Iterator iterator = query.iterate();
        while (iterator.hasNext()) {
            User user = (User)iterator.next();
            System.out.println(user.getName());
        }
        System.out.println("=====================================");
        iterator = query.iterate();
        while (iterator.hasNext()) {
            User user = (User)iterator.next();
            System.out.println(user.getName());
        }
        
        session.close();
        sessionFactory.close();
    }
}

执行结果：

Hibernate: select user0_.id as col_0_0_ from user user0_
Hibernate: select user0_.id as id0_1_, user0_.name as name0_1_, user0_.room_id as room3_0_1_, room1_.id as id1_0_, room1_.address as address1_0_ from user user0_ left outer join room room1_ on user0_.room_id=room1_.id where user0_.id=?
chenyan
Hibernate: select user0_.id as id0_1_, user0_.name as name0_1_, user0_.room_id as room3_0_1_, room1_.id as id1_0_, room1_.address as address1_0_ from user user0_ left outer join room room1_ on user0_.room_id=room1_.id where user0_.id=?
shenbin
=====================================
Hibernate: select user0_.id as col_0_0_ from user user0_
chenyan
shenbin

看见，Iterator中的元素并不是一次性返回的，而是一条一条返回的。当数据量庞大时，特性就会下降。

再看下面的测试代码：

package com.hb3.pack_22;


    
import java.io.IOException;
import java.sql.SQLException;
import java.util.Iterator;
import java.util.List;


    
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_22.model.User;


    
public class BusinessService {


    
    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();


    
        
        String hql = "from com.hb3.pack_22.model.User";
        
        Query query = session.createQuery(hql);
        
        List list = query.list();
        Iterator iterator = list.iterator();
        while (iterator.hasNext()) {
            User user = (User)iterator.next();
            System.out.println(user.getRoom().getAddress());
        }
//        System.out.println("====================================="); 
//        list = query.list(); 
//        iterator = list.iterator(); 
//        while (iterator.hasNext()) { 
//          User user = (User)iterator.next(); 
//          System.out.println(user.getRoom().getAddress()); 
//      } 
//         
//        System.out.println("++++++++++++++++++++++++++++++++++++++"); 
        
        query = session.createQuery(hql);
//        Iterator iterator = query.iterate(); 
//        while (iterator.hasNext()) { 
//          User user = (User)iterator.next(); 
//          System.out.println(user.getName()); 
//      } 
        System.out.println("=====================================");
        iterator = query.iterate();
        while (iterator.hasNext()) {
            User user = (User)iterator.next();
            System.out.println(user.getName());
        }
        
        session.close();
        sessionFactory.close();
    }
}

执行的结果为：

Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.room_id as room3_0_ from user user0_
Hibernate: select room0_.id as id1_0_, room0_.address as address1_0_ from room room0_ where room0_.id=?
NTU-M8-419
NTU-M8-419
=====================================
Hibernate: select user0_.id as col_0_0_ from user user0_
chenyan
shenbin

这明显在性能上要优于刚才的做法。可见，首次查询使用query.list性能要优于query.iterate，之后再做相同的查询请求时，则借助缓存机制，使用query.iterate会大大提高性能。

淘声依旧 2008-10-29 19:42 发表评论

hibernate3学习笔记(二十)｜关系映射：多对多

淘声依旧 — Wed, 29 Oct 2008 11:41:00 GMT

要实现多对多的对应，一般可以借由一个中间表来完成。也就是借由一对多，多对一来完成。

DDL：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default ''
);


    
CREATE TABLE user_server (
    user_id INT(11),
    server_id INT(11)
);


    
CREATE TABLE server (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    address VARCHAR(100) NOT NULL default ''
);

User.java

package com.hb3.pack_19.model;


    
import java.util.Set;


    
public class User {
    
    private Integer id;
    private String name;
    private Set servers;
    
    public User() {
    }


    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set getServers() {
        return servers;
    }
    public void setServers(Set servers) {
        this.servers = servers;
    }
}

Server.java

package com.hb3.pack_19.model;


    
import java.util.Set;


    
public class Server {


    
    private Integer id;
    private String address;
    private Set users;
    
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public Set getUsers() {
        return users;
    }
    public void setUsers(Set users) {
        this.users = users;
    }
}

Server.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_19.model.Server" table="server"> 

        <id name="id" column="id"> 
            <generator class="native"/> 
        id> 

        <property name="address" type="java.lang.String"/> 
        
        <set name="users" 
             table="user_server" 
             inverse="true" 
             cascade="save-update"> 
              
             <key column="server_id"/> 
             <many-to-many class="com.hb3.pack_19.model.User" 
                           column="user_id"/> 
        set> 
    class> 

hibernate-mapping>

User.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_19.model.User" table="user">
     
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 

        <property name="name" column="name" type="java.lang.String"/> 

        <set name="servers" 
             table="user_server" 
             cascade="save-update"> 
             
            <key column="user_id"/> 
            <many-to-many class="com.hb3.pack_19.model.Server" 
                          column="server_id"/>            
        set> 
    class> 

hibernate-mapping>

测试代码：

package com.hb3.pack_19;

import java.io.IOException;
import java.sql.SQLException;
import java.util.HashSet;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_19.model.Server;
import com.hb3.pack_19.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        Server server1 = new Server();
        server1.setAddress("PC-219"); 
        server1.setUsers(new HashSet());

        Server server2 = new Server(); 
        server2.setAddress("PC-220"); 
        server2.setUsers(new HashSet());
     
        Server server3 = new Server(); 
        server3.setAddress("PC-221");
        server3.setUsers(new HashSet());
     
        User user1 = new User(); 
        user1.setName("shenbin");
        user1.setServers(new HashSet());
     
        User user2 = new User(); 
        user2.setName("chenyan");
        user2.setServers(new HashSet());

        user1.getServers().add(server1); 
        user1.getServers().add(server2); 
        user1.getServers().add(server3); 
        server1.getUsers().add(user1); 
        server2.getUsers().add(user1); 
        server3.getUsers().add(user1); 

        user2.getServers().add(server1); 
        user2.getServers().add(server3); 
        server1.getUsers().add(user2); 
        server3.getUsers().add(user2); 
                
        Transaction tx= session.beginTransaction(); 
        session.save(user1); 
        session.save(user2);                 
        tx.commit();

        session.close();
        sessionFactory.close();
    }
}

但是，多对多映射由于使用了中介表格，查询效率不高。这不是一个很好的设计方式，应尽量避免多对多关联的设计。

淘声依旧 2008-10-29 19:41 发表评论

hibernate3学习笔记(十九)｜关系映射：一对一

淘声依旧 — Wed, 29 Oct 2008 11:40:00 GMT

A.唯一外键关联

DDL：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default '',
    room_id INT(11)
);


    
CREATE TABLE room (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    address VARCHAR(100) NOT NULL default ''
);

User.java

package com.hb3.pack_02.model;


    
public class User {


    
    private Integer id;
    private String name;
    private Room room;
    
    public User() {
    }


    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Room getRoom() {
        return room;
    }
    public void setRoom(Room room) {
        this.room = room;
    }
}

Room.java

package com.hb3.pack_02.model;


    
public class Room {


    
    private Integer id; 
    private String address;
    private User user;
    
    public Room() {
    }
    
    public Integer getId() { 
        return id; 
    } 
    public void setId(Integer id) { 
        this.id = id; 
    }
    public String getAddress() { 
        return address; 
    }
    public void setAddress(String address) { 
        this.address = address; 
    }
    public User getUser() {
        return user;
    }
    public void setUser(User user) {
        this.user = user;
    }
}

User.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_02.model.User" table="user"> 
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 

        <property name="name" column="name" type="java.lang.String"/> 
        
        <many-to-one name="room" 
                     column="room_id" 
                     class="com.hb3.pack_02.model.Room"
                     cascade="all"
                     outer-join="true"
                     unique="true"/>    
    class> 

hibernate-mapping>

Room.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_02.model.Room" table="room"> 
        <id name="id" column="id"> 
            <generator class="native"/> 
        id> 

        <property name="address" 
                  column="address" 
                  type="java.lang.String"/> 
                  
        <one-to-one name="user"
                    class="com.hb3.pack_02.model.User"
                    property-ref="room"/>
    class> 

hibernate-mapping>

测试代码：

package com.hb3.pack_02;


    
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_02.model.Room;
import com.hb3.pack_02.model.User;


    
public class BusinessService {


    
    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();


    
        User user1 = new User();
        user1.setName("shenbin"); 
        Room room1 = new Room(); 
        room1.setAddress("NTU-M8-419");
        user1.setRoom(room1);
   
        User user2 = new User(); 
        user2.setName("chanyan"); 
        Room room2 = new Room(); 
        room2.setAddress("NTU-M8-418");
        user2.setRoom(room2);
      
        Transaction tx = session.beginTransaction();
        session.save(user1);
        session.save(user2);        
        tx.commit();
        
        Room room = (Room) session.load(Room.class, new Integer(1));
        System.out.println(room.getUser().getName());
        
        session.close();
        sessionFactory.close();
    }
}

A.主键关联

DDL：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default ''
);


    
CREATE TABLE room (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    address VARCHAR(100) NOT NULL default ''
);

Room和User类同上。

Room.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_18.model.Room" table="room">
    
        <id name="id" column="id"> 
            <generator class="foreign"> 
                <param name="property">userparam>
            generator>
        id> 

        <property name="address" 
                  column="address" 
                  type="java.lang.String"/> 
                  
        <one-to-one name="user"
                    class="com.hb3.pack_18.model.User"
                    constrained="true"/>
    class> 

hibernate-mapping>

User.hbm.xml

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_18.model.User" table="user">
     
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 

        <property name="name" column="name" type="java.lang.String"/> 
        
        <one-to-one name="room" 
                    class="com.hb3.pack_18.model.Room"
                    cascade="all"/>
    class> 

hibernate-mapping>

测试代码：

package com.hb3.pack_18;

import java.io.IOException;
import java.sql.SQLException;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_18.model.Room;
import com.hb3.pack_18.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        User user1 = new User();
        user1.setName("chanyan"); 
        Room room1 = new Room(); 
        room1.setAddress("NTU-M8-419");
        user1.setRoom(room1);
        room1.setUser(user1);
                
        User user2 = new User(); 
        user2.setName("shenbin"); 
        Room room2 = new Room(); 
        room2.setAddress("NTU-M8-418");
        user2.setRoom(room2);
        room2.setUser(user2);
                
        Transaction tx = session.beginTransaction();
        session.save(user1);
        session.save(user2);
        tx.commit();

        session.close();
        sessionFactory.close();
    }
}

淘声依旧 2008-10-29 19:40 发表评论

hibernate3学习笔记(十八)｜关系映射：一对多

淘声依旧 — Wed, 29 Oct 2008 11:39:00 GMT

摘要: User对Room是多对一的关系，那么反过来Room对User就是一对多的关系了。 User.java： package com.hb3.pack_17.model; public class User { private&... 阅读全文

淘声依旧 2008-10-29 19:39 发表评论

hibernate3学习笔记(十七)｜关系映射：多对一

淘声依旧 — Wed, 29 Oct 2008 11:38:00 GMT

数据表设计如下图：

DDL文件：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default '',
    room_id INT(11)
);


    
CREATE TABLE room (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    address VARCHAR(100) NOT NULL default ''
);

Room.java

package com.hb3.pack_16.model;


    
public class Room {


    
    private Integer id; 
    private String address; 
    
    public Room() {
    }
    
    public Integer getId() { 
        return id; 
    } 
    public void setId(Integer id) { 
        this.id = id; 
    }
    public String getAddress() { 
        return address; 
    }
    public void setAddress(String address) { 
        this.address = address; 
    }
}

User.java

package com.hb3.pack_16.model;


    
public class User {


    
    private Integer id;
    private String name;
    private Room room;


    
    public User() {
    }


    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Room getRoom() {
        return room;
    }
    public void setRoom(Room room) {
        this.room = room;
    }
}

Room.hbm.xml：

xml version="1.0" encoding="utf-8"?>
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_16.model.Room" table="room">
    
        <id name="id" column="id"> 
            <generator class="native"/> 
        id> 

        <property name="address" 
                  column="address" 
                  type="java.lang.String"/> 
    class> 

hibernate-mapping>

User.hbm.xml：

xml version="1.0" encoding="utf-8"?>
    PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_16.model.User" table="user">
    
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 

        <property name="name" column="name" type="java.lang.String"/> 
        
        <many-to-one name="room" 
                     column="room_id" 
                     class="com.hb3.pack_16.model.Room"
                     cascade="all"
                     outer-join="true"/>         
    class> 

hibernate-mapping>

测试代码：

package com.hb3.pack_16;

import java.io.IOException;
import java.sql.SQLException;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_16.model.Room;
import com.hb3.pack_16.model.User;

public class BusinessService {

    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        Room room1 = new Room(); 
        room1.setAddress("NTU-M8-419"); 
        Room room2 = new Room(); 
        room2.setAddress("NTU-G3-302"); 
                
        User user1 = new User(); 
        user1.setName("shenbin"); 
        user1.setRoom(room1); 
                
        User user2 = new User(); 
        user2.setName("chenyan"); 
        user2.setRoom(room1); 
                
        User user3 = new User(); 
        user3.setName("yangye"); 
        user3.setRoom(room2); 

        Transaction tx = session.beginTransaction();   
        session.save(user1);
        session.save(user2);
        session.save(user3);    
        tx.commit();

        User user = (User) session.load(User.class, new Integer(1));
        System.out.println(user.getName());
        System.out.println(user.getRoom().getAddress());

        session.close();
        sessionFactory.close();
    }
}

在的设定中：

cascade表示操作时的级联关系。表示主控方在进行增删改操作时，被控方是否进行相关操作。

outer-join表示查询时是否使用外连接查询方式。

outer-join为true的时候，生成的查询SQL为：

Hibernate:
select user0_.id as id1_, user0_.name as name0_1_, user0_.room_id as room3_0_1_,
room1_.id as id0_, room1_.address as address1_0_ from user user0_
left outer join room room1_ on user0_.room_id=room1_.id where user0_.id=?

outer-join为false的时候，生成的查询SQL为：Hibernate:
select user0_.id as id0_, user0_.name as name0_0_, user0_.room_id as room3_0_0_
from user user0_ where user0_.id=?
Hibernate:
select room0_.id as id0_, room0_.address as address1_0_
from room room0_ where room0_.id=?

不过最好使用fetch属性来表示，及fetch="join"或者fetch="select"。

淘声依旧 2008-10-29 19:38 发表评论

hibernate3学习笔记(十五)｜继承映射

淘声依旧 — Wed, 29 Oct 2008 11:37:00 GMT

摘要: 这里详细讨论继承映射的3种方式： 1.Table per concrete class 继承关系如下图：数据表设计如下图： MySQL数据库中执行如下DDL： CREATE TABLE defaultuser ( id INT(11) NOT N... 阅读全文

淘声依旧 2008-10-29 19:37 发表评论

hibernate3学习笔记(十六)｜容器映射

淘声依旧 — Wed, 29 Oct 2008 11:37:00 GMT

摘要: 1.Set映射 DDL: CREATE TABLE user ( id INT(11) NOT NULL auto_increment PRIMARY KEY, na... 阅读全文

淘声依旧 2008-10-29 19:37 发表评论

hibernate3学习笔记(十四)｜Blob、Clob

淘声依旧 — Wed, 29 Oct 2008 11:36:00 GMT

在Hibernate中，可以直接对Blob、Clob作映射。

DDL如下：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default '',
    age INT,
    photo BLOB,
    resume TEXT
);

注意：由于BLOB字段大小不可预计，有时需要增大BLOB字段的大小，可在数据库中改用MEDIUMBLOB甚至LONGBLOB。

User.java

package com.hb3.pack_07.model;


    
import java.sql.Blob;
import java.sql.Clob;


    
public class User {


    
    private Integer id;
    private String name;
    private Integer age;
    private Blob photo;
    private Clob resume;
    
    public User() {
    }


    
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public Blob getPhoto() {
        return photo;
    }
    public void setPhoto(Blob photo) {
        this.photo = photo;
    }
    public Clob getResume() {
        return resume;
    }
    public void setResume(Clob resume) {
        this.resume = resume;
    }
}

User.hbm.xml文件：

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <class name="com.hb3.pack_07.model.User" table="user">
    
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id> 
        
        <property name="name" column="name" type="java.lang.String"/> 
        
        <property name="age" column="age" type="java.lang.Integer"/> 
        
        <property name="photo" column="photo" type="java.sql.Blob"/>   
              
        <property name="resume" column="resume" type="java.sql.Clob"/> 
        
    class>
    
hibernate-mapping>

修改hibernate.cfg.xml文件如下：

......

测试代码如下：

package com.hb3.pack_07;


    
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Blob;
import java.sql.Clob;
import java.sql.SQLException;


    
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_07.model.User;


    
public class BusinessService {


    
    public static void main(String[] args) throws IOException, SQLException {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();


    
        FileInputStream fileInputStream = new FileInputStream("c:\\sunset.jpg");
        Blob photo = Hibernate.createBlob(fileInputStream);
        Clob resume = Hibernate.createClob("Bla....Bla....resume text!!");
                
        User user = new User();
        user.setName("shenbin");
        user.setAge(new Integer(28));
        user.setPhoto(photo);
        user.setResume(resume);


    
        Transaction tx = session.beginTransaction();
        session.save(user); 
        tx.commit();
        
        session.close();
        session = sessionFactory.openSession();
        
        user = (User) session.load(User.class, new Integer(1));
        System.out.print(user.getAge() + "\t" +
                         user.getName() + "\t");
        String str_resume = user.getResume().getSubString(1, (int) user.getResume().length());
        System.out.println(str_resume);
        InputStream inputStream = user.getPhoto().getBinaryStream();
        FileOutputStream fileOutputStream = new FileOutputStream("c:\\sunset_save.jpg");
        byte[] buf = new byte[1];
        int len = 0;
        while((len = inputStream.read(buf)) != -1) {
            fileOutputStream.write(buf, 0, len);
        }
        inputStream.close();
        fileOutputStream.close();  
        System.out.println("save photo to c:\\sunset_save.jpg");


    
        session.close();
        sessionFactory.close();
    }
}

在MySQL中对BLOB以及CLOB类型的使用还是比较简单的，如果在Oracle DB中则相对复杂一些，计划在以后章节加以说明。

淘声依旧 2008-10-29 19:36 发表评论

hibernate3学习笔记(十三)｜Dynamic Model

淘声依旧 — Wed, 29 Oct 2008 11:35:00 GMT

在构造系统原型阶段，由于需求尚未确定，程序中的POJO会在开发过程中存在相当大的变动，于是在Hibernate3中引入了动态模型的概念。如此不需要事先实际定义POJO。

数据库DDL如下：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default '',
    age INT
);

User.hbm.xml配置文件中设定entity-name属性(属性值为查找的唯一标示符，不可重复)。

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <class entity-name="com.hb3.pack_06.model.DynamicUserModel" table="user">
    
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id>

        <property name="name" 
                  column="name" 
                  type="java.lang.String"/>  
                        
        <property name="age" 
                  column="age" 
                  type="java.lang.Integer"/>         
    class>
    
hibernate-mapping>

修改hibernate.cfg.xml配置文件：

......

测试代码如下：

package com.hb3.pack_06;

import java.util.HashMap;
import java.util.Map;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        Map userMap = new HashMap();
        userMap.put("name", "shenbin");
        userMap.put("age", new Integer(28));
                
        Transaction tx = session.beginTransaction();
        session.save("com.hb3.pack_06.model.DynamicUserModel", userMap);
        tx.commit();   
        
        session.close();
        session = sessionFactory.openSession();
        
        userMap = (Map) session.load("com.hb3.pack_06.model.DynamicUserModel", new Integer(1));
        System.out.println(userMap.get("name"));
        System.out.println(userMap.get("age"));
        
        session.close();
        sessionFactory.close();
    }
}

淘声依旧 2008-10-29 19:35 发表评论

hibernate3学习笔记(十一)｜复合主键

淘声依旧 — Wed, 29 Oct 2008 11:34:00 GMT

新建数据库User：

CREATE TABLE user (
    name VARCHAR(100) NOT NULL,
    phone VARCHAR(50) NOT NULL,
    age INT,
    PRIMARY KEY(name, phone)
);

现将name和phone定义成复合主键。分别使用2种方法如下：

方法1.复合主键字段直接包含在PO类中。

User.java（需要实现Serializable接口，并定义equals()和hashCode()方法）

package com.hb3.pack_03.model;

import java.io.Serializable;
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;

public class User implements Serializable {

    private static final long serialVersionUID = -8377583111386512407L;

    private String name;
    private String phone;
    private Integer age;
    
    public User() {
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }
    
    public boolean equals(Object obj) {
        if(obj == this) {
            return true;
        }
        
        if(!(obj instanceof User)) {
            return false;
        }
        
        User user = (User) obj;
        return new EqualsBuilder()
                 .append(this.name, user.getName())
                 .append(this.phone, user.getPhone())
                 .isEquals();
    }
    
    public int hashCode() {
        return new HashCodeBuilder()
                 .append(this.name)
                 .append(this.phone)
                 .toHashCode();
    }
}

在定义equals和hashCode方法时使用了apache的common-lang包。

User.hbm.xml文件：

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_03.model.User" table="user">
    
        <composite-id>
        
            <key-property name="name" 
                          column="name" 
                          type="java.lang.String"/>
            <key-property name="phone" 
                          column="phone" 
                          type="java.lang.String"/>
        composite-id>

        <property name="age" column="age" type="java.lang.Integer"/>
    
    class> 
    
hibernate-mapping>

hibernate.cfg.xml中修改：

......

测试代码如下：

package com.hb3.pack_03;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_03.model.User;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        User user = new User();
        user.setName("shenbin");
        user.setPhone("0970123456");
        user.setAge(28);
        Transaction tx = session.beginTransaction();
        session.save(user);
        tx.commit();
        
        user = (User) session.load(User.class, user);
                
        System.out.println(user.getAge() + "\t" +  user.getName() + "\t" + user.getPhone());

        session.close();
        sessionFactory.close();
    }
}

请注意：在实际测试过程中，如果数据库已经有数据存在，则不需要上面的黑题部分向数据库追加数据。

另外还请留意的是，光有session.save(user);而没有tx.commit();的话,数据不会被持久到数据库中的。

方法2.复合主键字段独立到另一个类中。

UserPK.java(需要实现Serializable接口，并定义equals()和hashCode()方法)

package com.hb3.pack_04.model;


    
import java.io.Serializable;


    
import org.apache.commons.lang.builder.EqualsBuilder;
import org.apache.commons.lang.builder.HashCodeBuilder;


    
public class UserPK implements Serializable {


    
    private static final long serialVersionUID = -2457999265373664790L;


    
    private String name;
    private String phone;


    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getPhone() {
        return phone;
    }
    public void setPhone(String phone) {
        this.phone = phone;
    }
    public boolean equals(Object obj) {
        if(obj == this) {
            return true;
        }
        
        if(!(obj instanceof User)) {
            return false;
        }
        
        UserPK pk = (UserPK) obj;
        return new EqualsBuilder()
                 .append(this.name, pk.getName())
                 .append(this.phone, pk.getPhone())
                 .isEquals();
    }
    
    public int hashCode() {
        return new HashCodeBuilder()
                 .append(this.name)
                 .append(this.phone)
                 .toHashCode();
    }
}

User.java

package com.hb3.pack_04.model;

import java.io.Serializable;

public class User implements Serializable {

    private static final long serialVersionUID = -8630481462628539996L;

    private UserPK userPK;
    private Integer age;
    
    public User() {
    }

    public UserPK getUserPK() {
        return userPK;
    }
    public void setUserPK(UserPK userPK) {
        this.userPK = userPK;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
}

User.hbm.xml文件：

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping> 

    <class name="com.hb3.pack_04.model.User" table="user">
    
        <composite-id name="userPK"
                      class="com.hb3.pack_04.model.UserPK"
                      unsaved-value="any">
            <key-property name="name" 
                          column="name" 
                          type="java.lang.String"/>
            <key-property name="phone" 
                          column="phone" 
                          type="java.lang.String"/>
        composite-id>
        
        <property name="age" column="age" type="java.lang.Integer"/>
    
    class> 

hibernate-mapping>

hibernate.cfg.xml中修改：

......

测试代码如下：

package com.hb3.pack_04;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_04.model.User;
import com.hb3.pack_04.model.UserPK;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        UserPK pk = new UserPK();
        pk.setName("shenbin");
        pk.setPhone("0970123456");
               
        User user = (User) session.load(User.class, pk);
               
        System.out.println(user.getAge() + 
                    "\t" + user.getUserPK().getName() + 
                    "\t" + user.getUserPK().getPhone());

        session.close();
        sessionFactory.close();
    }
}

淘声依旧 2008-10-29 19:34 发表评论

hibernate3学习笔记(十二)｜Component

淘声依旧 — Wed, 29 Oct 2008 11:34:00 GMT

在MySQL中新建数据表User：

CREATE TABLE user (
    id INT(11) NOT NULL auto_increment PRIMARY KEY,
    name VARCHAR(100) NOT NULL default '',
    age INT,
    email VARCHAR(100) NOT NULL
);

按照最基本的映射策略的话，应该把User类设计成：

package onlyfun.caterpillar; 

public class User { 
    private Integer id; 
    private String name; 
    private int age; 
    private String email; 

    ........ 
}

然而由于业务上的需要，要把email字段升格成MailAddress类，例如：

package com.hb3.pack_05.model;

public class MailAddress {

    private String email;

    public MailAddress() {       
    }
    
    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
    
    public void sendMail() {
        System.out.println("Send mail to " + email);
    }
}

User.java

package com.hb3.pack_05.model;

public class User {

    private Integer id;
    private String name;
    private Integer age;
    private MailAddress mailAddress;

    public User() {
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
    
    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public MailAddress getMailAddress() {
        return mailAddress;
    }

    public void setMailAddress(MailAddress mailAddress) {
        this.mailAddress = mailAddress;
    }
}

User.hbm.xml文件：

xml version="1.0" encoding="UTF-8"?>

    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping>

    <class name="com.hb3.pack_05.model.User" table="user">
    
        <id name="id" column="id" type="java.lang.Integer"> 
            <generator class="native"/> 
        id>
        
        <property name="name" column="name" type="java.lang.String"/>
        
        <property name="age" column="age" type="java.lang.Integer"/>
        
        <component name="mailAddress" class="com.hb3.pack_05.model.MailAddress"> 
            <property name="email" 
                      column="email" 
                      type="java.lang.String" 
                      not-null="true"/> 
        component> 
    class> 
hibernate-mapping>

修改hibernate.cfg.xml文件：

......

测试代码如下：

package com.hb3.pack_05;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_05.model.MailAddress;
import com.hb3.pack_05.model.User;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        MailAddress mailAddress = new MailAddress();
        mailAddress.setEmail("bluelazysb@hotmail.com");
                
        User user = new User();
        user.setName("shenbin");
        user.setAge(new Integer(28));
        user.setMailAddress(mailAddress);

        Transaction tx = session.beginTransaction();            
        session.save(user);
        session.flush();
        tx.commit();

        session.close();
        
        session = sessionFactory.openSession();
        
        user = (User) session.load(User.class, new Integer(1));
        System.out.println(user.getAge()  + "\t" +
                           user.getName() + "\t" +
                           user.getMailAddress().getEmail());
        user.getMailAddress().sendMail();
        
        session.close();
        sessionFactory.close();
    }
}

淘声依旧 2008-10-29 19:34 发表评论

hibernate3学习笔记(十)｜SQL支援

淘声依旧 — Wed, 29 Oct 2008 11:33:00 GMT

示例代码如下：

package com.hb3.pack_01;


    
import java.util.Iterator;


    
import org.hibernate.Query;
import org.hibernate.SQLQuery;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_01.model.User;


    
public class BusinessService {


    
    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();
        
        String sql = "select {user.*} from User user where user.age > ?";
        SQLQuery sqlQuery = session.createSQLQuery(sql);
        sqlQuery.setParameter(0, 20);
        sqlQuery.addEntity("user", User.class);
        Iterator iterator = sqlQuery.list().iterator();
        while(iterator.hasNext()) {
            User user = (User) iterator.next();
            System.out.println(user.getAge() + "\t" + user.getName());
        }
        
        Query query = session.getNamedQuery("com.hb3.pack_01.model.User.SQLQueryUser");
        query.setInteger("age", 20);
        iterator = query.list().iterator();
        while(iterator.hasNext()) {
            User user = (User) iterator.next();
            System.out.println(user.getAge() + "\t" + user.getName());
        }


    
        session.close();
        sessionFactory.close();
    }
}

修改User.hbm.xml文件如下：

xml version="1.0" encoding="UTF-8"?>


    
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">


    
<hibernate-mapping>
    <class name="com.hb3.pack_01.model.User" table="user" 
        dynamic-insert="true" 
        dynamic-update="true"   
    >
        <id name="id" column="id" type="java.lang.Integer" unsaved-value="null">
            <generator class="native" />
        id>
        
        <property name="name" column="name" type="java.lang.String" />
        
        <property name="age" column="age" type="java.lang.Integer" />
    class>
    
    <query name="com.hb3.pack_01.model.User.QueryUser">
        
            from User as user where user.age > :minAge        
        ]]>
    query>
    
    <sql-query name="com.hb3.pack_01.model.User.SQLQueryUser">
        
            select {user.*} from User user where user.age > :age
        ]]>        
        <return alias="user" class="com.hb3.pack_01.model.User"/>
    sql-query>
    
hibernate-mapping>

运行结果：

17:20:40,859 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
17:20:41,281 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
17:20:41,312 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: select user.id as id0_0_, user.name as name0_0_, user.age as age0_0_ from User user where user.age > ?
28 shenbin
24 chenyan
23 shenyi
23 yangye
22 chenyong
Hibernate: select user.id as id0_0_, user.name as name0_0_, user.age as age0_0_ from User user where user.age > ?
28 shenbin
24 chenyan
23 shenyi
23 yangye
22 chenyong

另外，我们还可以自定义insert、update、delete时的SQL文而不使用Hibernate3自动生成的SQL文。

修改User.hbm.xml文件如下：

xml version="1.0" encoding="UTF-8"?>


    
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">


    
<hibernate-mapping>
    <class name="com.hb3.pack_01.model.User" table="user" 
        dynamic-insert="true" 
        dynamic-update="true"   
    >
        <id name="id" column="id" type="java.lang.Integer" unsaved-value="null">
            <generator class="native" />
        id>
        
        <property name="name" column="name" type="java.lang.String" />
        
        <property name="age" column="age" type="java.lang.Integer" />
    
        <sql-insert>
            
            INSERT INTO user VALUES (?, ?)   
        sql-insert>
        <sql-update>
            UPDATE user SET name=?, age=?, WHERE id=?        
        sql-update>
        <sql-delete>
            DELETE FROM user WHERE id=?        
        sql-delete>
        
    class>
    
    <query name="com.hb3.pack_01.model.User.QueryUser">
        
            from User as user where user.age > :minAge        
        ]]>
    query>
    
    <sql-query name="com.hb3.pack_01.model.User.SQLQueryUser">
        
            select {user.*} from User user where user.age > :age
        ]]>        
        <return alias="user" class="com.hb3.pack_01.model.User"/>
    sql-query>
    
hibernate-mapping>

示例代码：

package com.hb3.pack_01;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import com.hb3.pack_01.model.User;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();

        User user = new User();
        user.setName("yanfeng");
        user.setAge(21);
        Transaction tx = session.beginTransaction();
        session.save(user); 
        tx.commit(); 
        
        session.close();
        sessionFactory.close();
    }
}

测试结果如下：

17:29:03,781 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
17:29:04,328 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
17:29:04,359 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: insert into user (name, age) values (?, ?)

可见，在实行保存操作时的SQL确实是我们在配置文件中定义的SQL文。

淘声依旧 2008-10-29 19:33 发表评论

hibernate3学习笔记(八)｜DetachedCriteria

淘声依旧 — Wed, 29 Oct 2008 11:32:00 GMT

示例代码如下：

package com.hb3.pack_01;

import java.util.Iterator;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.DetachedCriteria;
import org.hibernate.criterion.Restrictions;

import com.hb3.pack_01.model.User;

public class BusinessService {

    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        
        DetachedCriteria detchedCriteria = DetachedCriteria.forClass(User.class);
        detchedCriteria.add(Restrictions.ge("age",new Integer(20)));
        
        Session session = sessionFactory.openSession();
        Criteria criteria = detchedCriteria.getExecutableCriteria(session); 
        
        List users = criteria.list();
        Iterator iterator =  users.iterator();
        System.out.println("id \t name/age");
        while(iterator.hasNext()) {
            User ur = (User) iterator.next();
            System.out.println(ur.getId() + " \t " + ur.getName() + "/" + ur.getAge());    
        }
        
        session.close();
        sessionFactory.close();
    }
}

Criteria和Session绑定的，但DetachedCriteria则不同。

这是在Hibernate 3中新增的类，目的是为了能够重复使用Criteria。其使用方法请参看前面对Criteria的介绍：

淘声依旧 2008-10-29 19:32 发表评论

hibernate3学习笔记(九)｜Query及HQL

淘声依旧 — Wed, 29 Oct 2008 11:32:00 GMT

示例代码如下：

package com.hb3.pack_01;


    
import java.util.Iterator;
import java.util.List;


    
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;


    
import com.hb3.pack_01.model.User;
import com.hb3.pack_01.model.UserBak;


    
public class BusinessService {


    
    public static void main(String[] args) {
        
        Configuration config = new Configuration().configure();
        SessionFactory sessionFactory = config.buildSessionFactory();      
        Session session = sessionFactory.openSession();
        
        Query query = session.createQuery("from com.hb3.pack_01.model.User user order by user.age desc, user.name");//[== from User] 
        printUserInfo(query.list());
        
        query = session.createQuery("select new com.hb3.pack_01.model.UserBak(user.name, user.age) from User as user");
        Iterator iterator = query.list().iterator();
        System.out.println("class_name \t\t name/age");
        while (iterator.hasNext()) {
            UserBak userbak = (UserBak) iterator.next();
            System.out.println(userbak.getClz() + " \t " + userbak.getName() + "/" + userbak.getAge());
        }
        
        query = session.createQuery("select upper(user.name) from User as user where (user.age/2 >= ?) and (user.age is not null)"); 
        query.setInteger(0, 13);
        List names = query.list();
        iterator =  names.iterator();
        while(iterator.hasNext()) {
            System.out.println(iterator.next());
        }
        
        query = session.createQuery("select user.name, user.age from User as user where user.age > :minAge"); 
        query.setInteger("minAge", 25);
        names = query.list();
        iterator =  names.iterator();
        while(iterator.hasNext()) {
            Object[] obj = (Object[]) iterator.next();
            System.out.println(obj[0] + "\t" + obj[1]);
        }
        
        query = session.getNamedQuery("com.hb3.pack_01.model.User.QueryUser"); 
        query.setInteger("minAge", 25);
        printUserInfo(query.list());
        
        Transaction tx= session.beginTransaction();
        query = session.createQuery("update User set age=24 where name='chenyan'");
        query.executeUpdate();
        tx.commit();


    
        tx= session.beginTransaction();
        query = session.createQuery("delete User where name='yaobin'");
        query.executeUpdate();
        tx.commit();
        
        session.close();
        sessionFactory.close();
    }
    
    public static void printUserInfo(List users){
        
        Iterator iterator = users.iterator();
        System.out.println("id \t name/age");
        while (iterator.hasNext()) {
            User user = (User) iterator.next();
            System.out.println(user.getId() + " \t " + user.getName() + "/" + user.getAge());
        }
    }
}

修改User.hbm.xml文件;

xml version="1.0" encoding="UTF-8"?>


    
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">


    
<hibernate-mapping>
    <class name="com.hb3.pack_01.model.User" table="user" 
        dynamic-insert="true" 
        dynamic-update="true"   
    >
        <id name="id" column="id" type="java.lang.Integer" unsaved-value="null">
            <generator class="native" />
        id>
        
        <property name="name" column="name" type="java.lang.String" />
        
        <property name="age" column="age" type="java.lang.Integer" />
    class>
    
    <query name="com.hb3.pack_01.model.User.QueryUser">
        
            from User as user where user.age >  :minAge        
        ]]>
    query>
    
hibernate-mapping>

新建UserBak类

package com.hb3.pack_01.model;


    
public class UserBak {


    
    private String clz = "UserBak";
    private String name;
    private Integer age;
    
    public UserBak() {
    }
    
    public UserBak(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Integer getAge() {
        return age;
    }
    public void setAge(Integer age) {
        this.age = age;
    }
    public String getClz() {
        return clz;
    }
    public void setClz(String clz) {
        this.clz = clz;
    }
}

运行结果：

16:53:02,015 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
16:53:02,437 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
16:53:02,468 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.age as age0_ from user user0_ order by user0_.age desc, user0_.name
id name/age
1 shenbin/28
2 chenyan/26
9 shenyi/23
10 yangye/23
11 chenyong/22
13 chendong/null
12 yaobin/null
Hibernate: select user0_.name as col_0_0_, user0_.age as col_1_0_ from user user0_
class_name name/age
UserBak shenbin/28
UserBak chenyan/26
UserBak shenyi/23
UserBak yangye/23
UserBak chenyong/22
UserBak yaobin/null
UserBak chendong/null
Hibernate: select upper(user0_.name) as col_0_0_ from user user0_ where user0_.age/2>=? and (user0_.age is not null)
SHENBIN
CHENYAN
Hibernate: select user0_.name as col_0_0_, user0_.age as col_1_0_ from user user0_ where user0_.age>?
shenbin 28
chenyan 26
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.age as age0_ from user user0_ where user0_.age>?
id name/age
1 shenbin/28
2 chenyan/26
Hibernate: update user set age=24 where name='chenyan'
Hibernate: delete from user where name='yaobin'

注意点：

1.在Hibernate3中，可以直接使用HQL指定更新或刪除。

2.使用HQL可以自定义返回的类型。（如:UserBak）

3.使用HQL可以结合各种查询条件，使用where子句限定查询条件，除了 = 运算之外，还有 >、>=、<、<=、!= 或 <>等比较运算：

Query query = session.createQuery("from User user where user.age between 20 and 30");

Query query = session.createQuery("from User user where user.name in('caterpillar', 'momor')");

Query query = session.createQuery("from User user where user.name like 'cater%'");

Query query = session.createQuery("select avg(user.age) from User as user");

Query query = session.createQuery("select count(*) from User as user");

也可以配合GROUP BY子句，假设在数据库表中追加一个Sex字段。

Query query = session.createQuery("select user.sex, avg(user.age) from User user group by user.sex");

运行结果可能是：

+-------------------------------+ 

|    sex       |    avg(age)    | 

+-------------------------------+ 

|    male      |    30          | 

+-------------------------------+ 

|    female    |    25          | 

+-------------------------------+

可以結合having子句,例如只将平均年龄大于20的资料分组显示出来：
Query query = session.createQuery("select user.sex, avg(user.age) from User user group by user.sex having avg(user.age) > 20");

使用HQL是官方推荐的查询方式。

淘声依旧 2008-10-29 19:32 发表评论

hibernate3学习笔记(七)｜Criteria Queries

淘声依旧 — Wed, 29 Oct 2008 11:31:00 GMT

示例代码如下：

package com.hb3.pack_01;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Hibernate;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Example;
import org.hibernate.criterion.Order;
import org.hibernate.criterion.ProjectionList;
import org.hibernate.criterion.Projections;
import org.hibernate.criterion.Property;
import org.hibernate.criterion.Restrictions;
import org.hibernate.type.Type;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
Criteria criteria = session.createCriteria(User.class);
criteria.addOrder(Order.asc("age"));
List users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
criteria.add(Restrictions.gt("age", new Integer(22)));
criteria.add(Restrictions.lt("age", new Integer(27)));
users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
criteria.add(Restrictions.or(
Restrictions.eq("age", new Integer(23)),
Restrictions.isNull("age")
));
users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
criteria.add(Restrictions.sqlRestriction("{alias}.name LIKE (?)", "%ya%", Hibernate.STRING));
users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
Integer[] ages = {new Integer(26), new Integer(28)};
Type[] types = {Hibernate.INTEGER, Hibernate.INTEGER};
criteria.add(Restrictions.sqlRestriction("{alias}.age BETWEEN (?) AND (?)", ages, types));
users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
criteria.setFirstResult(3);
criteria.setMaxResults(2);
users = criteria.list();
printUserInfo(users);
criteria = session.createCriteria(User.class);
criteria.setProjection(Projections.rowCount());
users = criteria.list();
Iterator iterator = users.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
criteria = session.createCriteria(User.class);
criteria.setProjection(Projections.avg("age"));
users = criteria.list();
iterator = users.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
criteria = session.createCriteria(User.class);
criteria.setProjection(Projections.groupProperty("age"));
users = criteria.list();
iterator = users.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
ProjectionList projectionList = Projections.projectionList();
projectionList.add(Projections.groupProperty("age"));
projectionList.add(Projections.groupProperty("name"));
projectionList.add(Projections.rowCount());
criteria = session.createCriteria(User.class);
criteria.setProjection(projectionList);
users = criteria.list();
iterator = users.iterator();
while(iterator.hasNext()) {
Object[] o = (Object[]) iterator.next();
System.out.println(o[0] + ""t" + o[1] + ""t" + o[2]);
}
criteria = session.createCriteria(User.class);
criteria.add(Property.forName("name").like("%ya%"));
criteria.addOrder(Property.forName("age").desc());
users = criteria.list();
printUserInfo(users);
User user = new User();
user.setAge(new Integer(26));
criteria = session.createCriteria(User.class);
criteria.add(Example.create(user));
users = criteria.list();
printUserInfo(users);
session.close();
sessionFactory.close();
}
public static void printUserInfo(List users){
Iterator iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
}
}

运行结果如下：

15:41:36,312 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
15:41:36,750 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
15:41:36,781 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ order by this_.age asc
id name/age
11 yangye/null
12 yangye/null
9 yangye/23
10 yangye/23
2 chenyan/26
1 shenbin/28
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where this_.age>? and this_.age id name/age
2 chenyan/26
9 yangye/23
10 yangye/23
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where (this_.age=? or this_.age is null)
id name/age
9 yangye/23
10 yangye/23
11 yangye/null
12 yangye/null
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where this_.name LIKE (?)
id name/age
2 chenyan/26
9 yangye/23
10 yangye/23
11 yangye/null
12 yangye/null
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where this_.age BETWEEN (?) AND (?)
id name/age
1 shenbin/28
2 chenyan/26
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ limit ?, ?
id name/age
10 yangye/23
11 yangye/null
Hibernate: select count(*) as y0_ from user this_
6
Hibernate: select avg(this_.age) as y0_ from user this_
25.0
Hibernate: select this_.age as y0_ from user this_ group by this_.age
null
23
26
28
Hibernate: select this_.age as y0_, this_.name as y1_, count(*) as y2_ from user this_ group by this_.age, this_.name
null yangye 2
23 yangye 2
26 chenyan 1
28 shenbin 1
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where this_.name like ? order by this_.age desc
id name/age
2 chenyan/26
9 yangye/23
10 yangye/23
11 yangye/null
12 yangye/null
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where (this_.age=?)
id name/age
2 chenyan/26

注意：

Restrictions的几个常用限定查询方法如下表所示：

方法	说明
Restrictions.eq	等于
Restrictions.allEq	使用Map，使用key/value进行多个等于的比对
Restrictions.gt	大于 >
Restrictions.ge	大于等于 >=
Restrictions.lt	小于 <
Restrictions.le	小于等于 <=
Restrictions.between	对应SQL的BETWEEN子句
Restrictions.like	对应SQL的LIKE子句
Restrictions.in	对应SQL的in子句
Restrictions.and	and关系
Restrictions.or	or关系
Restrictions.sqlRestriction	SQL限定查询

此外，Criteria还可以进行复合查询。即在原有的查询基础上再进行查询，例如在Room对User的一对多关系中，在查询出所有的Room資料之后，希望再查询users中"age"为30的user資料：

Criteria roomCriteria = session.createCriteria(Room.class);
Criteria userCriteria = roomCriteria.createCriteria("users");
userCriteria.add(Restrictions.eq("age", new Integer(30)));
List rooms = roomCriteria.list(); // 只列出users属性中有user之"age"为30的Room
Iterator iterator = rooms.iterator();

这个涉及到对象的关联映射，在后续章节中还会着重讲述。

淘声依旧 2008-10-29 19:31 发表评论

hibernate3学习笔记(六)｜Session管理

淘声依旧 — Wed, 29 Oct 2008 11:30:00 GMT

请注意，在hibernate中SessionFactory是被设计成线程安全(Thread-safe)的,遗憾的是，Session却线程不安全。

这就意味着:有可能多个线程共享并操作同一个Session从而很容易使数据混乱。

解决的办法如下：（其实hibernate的文档中早已经提过了）

新建HibernateUtil类：

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.*;
import org.hibernate.cfg.*;
public class HibernateUtil {
private static Log log = LogFactory.getLog(HibernateUtil.class);
private static final SessionFactory sessionFactory;
static {
try {
// Create the SessionFactory
sessionFactory = new Configuration().configure()
.buildSessionFactory();
} catch (Throwable ex) {
// Make sure you log the exception, as it might be swallowed
log.error("Initial SessionFactory creation failed.", ex);
throw new ExceptionInInitializerError(ex);
}
}
public static final ThreadLocal session = new ThreadLocal();
public static Session currentSession() {
Session s = (Session) session.get();
// Open a new Session, if this Thread has none yet
if (s == null) {
s = sessionFactory.openSession();
session.set(s);
}
return s;
}
public static void closeSession() {
Session s = (Session) session.get();
if (s != null) {
s.close();
}
session.set(null);
}
}

这样，在程序中可这样调用：

Session session = HibernateUtil.currentSession();
User user = (User) session.load(User.class, new Integer(1));
System.out.println(user.getName());
HibernateUtil.closeSession();

在web应用中，可以借由Filter来进行session管理。在需要session的时候开启session，在request结束之后关闭session。

HibernateSessionUtil.java

import java.io.Serializable;
import net.sf.hibernate.HibernateException;
import net.sf.hibernate.Session;
import net.sf.hibernate.SessionFactory;
import net.sf.hibernate.Transaction;
public class HibernateSessionUtil implements Serializable
{
public static final ThreadLocal tLocalsess = new ThreadLocal();
public static final ThreadLocal tLocaltx = new ThreadLocal();
/*
* getting the thread-safe session for using
*/
public static Session currentSession(){
Session session = (Session) tLocalsess.get();
//open a new one, if none can be found.
try{
if (session == null){
session = openSession();
tLocalsess.set(session);
}
}catch (HibernateException e){
throw new InfrastructureException(e);
}
return session;
}
/*
* closing the thread-safe session
*/
public static void closeSession(){
Session session = (Session) tLocalsess.get();
tLocalsess.set(null);
try{
if (session != null && session.isOpen()){
session.close();
}
}catch (HibernateException e){
throw new InfrastructureException(e);
}
}
/*
* begin the transaction
*/
public static void beginTransaction(){
Transaction tx = (Transaction) tLocaltx.get();
try{
if (tx == null){
tx = currentSession().beginTransaction();
tLocaltx.set(tx);
}
}catch (HibernateException e){
throw new InfrastructureException(e);
}
}
/*
* close the transaction
*/
public static void commitTransaction(){
Transaction tx = (Transaction) tLocaltx.get();
try{
if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack())
tx.commit();
tLocaltx.set(null);
}catch (HibernateException e){
throw new InfrastructureException(e);
}
}
/*
* for rollbacking
*/
public static void rollbackTransaction(){
Transaction tx = (Transaction) tLocaltx.get();
try{
tLocaltx.set(null);
if (tx != null && !tx.wasCommitted() && !tx.wasRolledBack()){
tx.rollback();
}
}catch (HibernateException e){
throw new InfrastructureException(e);
}
}
private static Session openSession() throws HibernateException{
return getSessionFactory().openSession();
}
private static SessionFactory getSessionFactory() throws HibernateException{
return SingletonSessionFactory.getInstance();
}
}

filter中则：

public class HibernateSessionCloser implements Filter{
protected FilterConfig filterConfig = null;
public void init(FilterConfig filterConfig)throws ServletException{
this.filterConfig = filterConfig;
}
public void destroy(){
this.filterConfig = null;
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
throws IOException, ServletException {
try{
chain.doFilter(request, response);
}
finally{
try{
HibernateSessionUtil.commitTransaction();
}catch (InfrastructureException e){
HibernateSessionUtil.rollbackTransaction();
}finally{
HibernateSessionUtil.closeSession();
}
}
}
}

然后在操作数据库前加上

HibernateSessionUtil.beginTransaction();
HibernateSessionUtil.currentSession();//取得Session

淘声依旧 2008-10-29 19:30 发表评论

hibernate3学习笔记(五)｜saveOrUpdate方法

淘声依旧 — Wed, 29 Oct 2008 11:29:00 GMT

修改User.hbm.xml文件如下：

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
dynamic-insert="true"
dynamic-update="true"
>
unsaved-value="null">

测试代码：

package com.hb3.pack_01;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
Criteria criteria = session.createCriteria(User.class);
List users = criteria.list();
Iterator iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
session.close();
System.out.println("========================================");
session = sessionFactory.openSession();
User user = new User();
user.setId(2);
user.setName("chenyan");
user.setAge(new Integer(24));
Transaction tx = session.beginTransaction();
session.saveOrUpdate(user);
tx.commit();
System.out.println("========================================");
user = new User();
user.setName("yangye");
user.setAge(new Integer(23));
tx = session.beginTransaction();
session.saveOrUpdate(user);
tx.commit();
System.out.println("========================================");
Query query = session.createQuery("from User");
users = query.list();
iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
session.close();
sessionFactory.close();
}
}

运行结果：

13:45:00,140 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
13:45:00,703 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
13:45:00,734 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_
id name/age
1 shenbin/28
2 chenyan/25
========================================
Hibernate: update user set name=?, age=? where id=?
========================================
Hibernate: insert into user (name, age) values (?, ?)
========================================
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.age as age0_ from user user0_
id name/age
1 shenbin/28
2 chenyan/24
3 yangye/23

提示：

unsaved-value可以设定的值包括：

any：总是存储

none：总是更新

null：id为null时存储（默认）

valid：id为null或是指定值时存储

值得一提的是：

正如上面的代码所示，使用查询语句查出对象后，不能使用同一个session直接对对象进行修改操作。否则会抛出异常：

Exception in thread "main" org.hibernate.NonUniqueObjectException: a different object with the same identifier value was already associated with the session: [com.hb3.pack_01.model.User#2]

......

当然这并不是saveOrUpdate方法独有的。save和update等方法使用不当也会出现如上异常。

解决方法可新建session, 或参阅：

http://www.blogjava.net/Unmi/archive/2007/08/10/135771.html

http://blog.csdn.net/tmpfree/archive/2006/03/13/623516.aspx

http://www.javaeye.com/topic/11581

淘声依旧 2008-10-29 19:29 发表评论

hibernate3学习笔记(四)｜增删改查

淘声依旧 — Wed, 29 Oct 2008 11:28:00 GMT

测试代码：

package com.hb3.pack_01;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
//insert
User user = new User();
user.setName("chenyan");
//user.setAge(new Integer(23));
Transaction tx = session.beginTransaction();
session.save(user);
tx.commit();
//get
user = (User) session.get(User.class, user.getId());
System.out.println(user.getAge());
//update
user.setAge(new Integer(24));
tx= session.beginTransaction();
session.update(user);
tx.commit();
//load
user = (User) session.load(User.class, user.getId());
System.out.println(user.getAge());
//delete
        tx = session.beginTransaction();
        session.delete(user);
        tx.commit();
session.close();
sessionFactory.close();
}
}

执行结果：

11:50:50,750 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
11:50:51,156 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
11:50:51,171 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: insert into user (name, age) values (?, ?)
null
Hibernate: update user set name=?, age=? where id=?
24

修改User.hbm.xml文件如下：

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
dynamic-insert="true"
dynamic-update="true"
>

运行结果如下：

12:46:32,062 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
12:46:32,468 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
12:46:32,500 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: insert into user (name) values (?)
null
Hibernate: update user set age=? where id=?
24
Hibernate: delete from user where id=?

可见：

dynamic-insert和dynamic-update设成true后，分别表示生成的SQL中只插入非空字段以及只修改改变过的字段。

另外,hibernate还提供了saveOrUpdate()方法，因为这个方法很容易出错，故在后续章节着重讲述。

关于查询：

package com.hb3.pack_01;
import java.util.Iterator;
import java.util.List;
import org.hibernate.Criteria;
import org.hibernate.Query;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.criterion.Restrictions;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
Criteria criteria = session.createCriteria(User.class);
List users = criteria.list();
Iterator iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
//criteria.add(Expression.eq("name", "shenbin"));
criteria.add(Restrictions.eq("name", "shenbin"));
users = criteria.list();
iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
System.out.println("====================================================");
Query query = session.createQuery("from User");
users = query.list();
iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
query = session.createQuery("from User user where user.name like ?");
query.setParameter(0, "shenbin");
users = query.list();
iterator = users.iterator();
System.out.println("id "t name/age");
while (iterator.hasNext()) {
User user = (User) iterator.next();
System.out.println(user.getId() + " "t " + user.getName() + "/" + user.getAge());
}
session.close();
sessionFactory.close();
}
}

执行结果：

13:05:43,031 WARN ConfigurationFactory:127 - No configuration found. Configuring ehcache from ehcache-failsafe.xml found in the classpath: jar:file:/D:/Java/MyEclipse%206.0/workspace/hb3demo/ehcache-1.2.3.jar!/ehcache-failsafe.xml
13:05:43,453 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.UpdateTimestampsCache]; using defaults.
13:05:43,484 WARN EhCacheProvider:93 - Could not find configuration [org.hibernate.cache.StandardQueryCache]; using defaults.
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_
id name/age
1 shenbin/29
2 chenyan/24
3 chenyan/24
4 chenyan/24
Hibernate: select this_.id as id0_0_, this_.name as name0_0_, this_.age as age0_0_ from user this_ where this_.name=?
id name/age
1 shenbin/29
================================================
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.age as age0_ from user user0_
id name/age
1 shenbin/29
2 chenyan/24
3 chenyan/24
4 chenyan/24
Hibernate: select user0_.id as id0_, user0_.name as name0_, user0_.age as age0_ from user user0_ where user0_.name like ?
id name/age
1 shenbin/29

以上分别演示了使用Criteria对SQL的分装以及透过HQL来进行查询。

注意：

代码中如下部分

//criteria.add(Expression.eq("name", "shenbin"));
criteria.add(Restrictions.eq("name", "shenbin"));

在hibernate3.3以后的版本，可能Expression类会被废除，为了保证代码的向后兼容，请使用Restrictions替代。

淘声依旧 2008-10-29 19:28 发表评论

hibernate3学习笔记(三)｜数据加载——Session.get/load

淘声依旧 — Wed, 29 Oct 2008 11:27:00 GMT

Session.load/get方法均可以根据指定的实体类和id从数据库读取记录，并返回与之对应的实体对象。其区别在于：

如果未能发现符合条件的记录，get方法返回null，而load方法会抛出一个ObjectNotFoundException。
Load方法可返回实体的代理类实例，而get方法永远直接返回实体类。
load方法可以充分利用内部缓存和二级缓存中的现有数据，而get方法则仅仅在内部缓存中进行数据查找，如没有发现对应数据，将越过二级缓存，直接调用SQL完成数据读取。

Session在加载实体对象时，将经过的过程：

首先，Hibernate中维持了两级缓存。第一级缓存由Session实例维护，其中保持了Session当前所有关联实体的数据，也称为内部缓存。而第二级缓存则存在于SessionFactory层次，由当前所有由本SessionFactory构造的Session实例共享。出于性能考虑，避免无谓的数据库访问，Session在调用数据库查询功能之前，会先在缓存中进行查询。首先在第一级缓存中，通过实体类型和id进行查找，如果第一级缓存查找命中，且数据状态合法，则直接返回。之后，Session会在当前“NonExists”记录中进行查找，如果“NonExists”记录中存在同样的查询条件，则返回null。 “NonExists”记录了当前Session实例在之前所有查询操作中，未能查询到有效数据的查询条件（相当于一个查询黑名单列表）。如此一来，如果 Session中一个无效的查询条件重复出现，即可迅速作出判断，从而获得最佳的性能表现。

对于load方法而言，如果内部缓存中未发现有效数据，则查询第二级缓存，如果第二级缓存命中，则返回。如在缓存中未发现有效数据，则发起数据库查询操作（Select SQL），如经过查询未发现对应记录，则将此次查询的信息在“NonExists”中加以记录，并返回null。根据映射配置和Select SQL得到的ResultSet，创建对应的数据对象。将其数据对象纳入当前Session实体管理容器（一级缓存）。执行Interceptor.onLoad方法（如果有对应的Interceptor）。将数据对象纳入二级缓存。如果数据对象实现了LifeCycle接口，则调用数据对象的onLoad方法。返回数据对象。

另外值得注意的是：（接前面的例子）

User user1 = (User) session.get(User.class, new Integer(1));
User user2 = (User) session.load(User.class, new Integer(1));

和

User user2 = (User) session.load(User.class, new Integer(1));

User user1 = (User) session.get(User.class, new Integer(1));
仅仅执行的顺序不同，但取数据使用的机制是不同的。

如下图所示：

很明显，在执行session.get之前从来没有执行过session.load，则session.get直接返回实体而不使用ｐｒｏｘｙ。在这之后若使用session.load也将直接返回实体。

但是如果由session.load先执行，则一定不会直接返回对象实体的。因为他优先考虑从缓存中返回数据。

淘声依旧 2008-10-29 19:27 发表评论

hibernate3学习笔记(二)｜一级缓存

淘声依旧 — Wed, 29 Oct 2008 11:25:00 GMT

修改BusinessService．ｊａｖａ文件如下所示：

package com.hb3.pack_01;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
User user1 = (User) session.load(User.class, new Integer(1));
User user2 = (User) session.load(User.class, new Integer(1));
System.out.println(user1 == user2);
user1 = (User) session.load(User.class, new Integer(1));
session.evict(user1);
user2 = (User) session.load(User.class, new Integer(1));
System.out.println(user1 == user2);
user1 = (User) session.load(User.class, new Integer(1));
session.clear();
user2 = (User) session.load(User.class, new Integer(1));
System.out.println(user1 == user2);
Session session1 = sessionFactory.openSession();
user1 = (User) session1.load(User.class, new Integer(1));
session1.close();
Session session2 = sessionFactory.openSession();
user2 = (User)session2.load(User.class, new Integer(1));
session2.close();
System.out.println(user1 == user2);
session.close();
sessionFactory.close();
}
}

依次打印出的结果为

true
false
false
false

可见：

使用session.evict或者session.clear把某个物体从缓存中移除，或者直接关闭Session，都会使缓存失效，或者说释放缓存占用的资源空间。

值得一提的是：在载入大量数据时，应该及时手动清除一级缓存以释放资源。

例如：

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
while(....) { // 大量載入物件時的迴圈示意
....
session.save(someObject);
if(count % 100 == 0) { // 每100筆資料
session.flush(); // 送入資料庫
session.clear(); // 清除快取
}
}
tx.commit();
session.close();

在SQL Server、Oracle等数据库可使用ｈｉｂｅｒｎａｔｅ的配置文件进行配置，如：

....
....
100
....

注意：在MySQL中不支持这种配置方式。

淘声依旧 2008-10-29 19:25 发表评论

hibernate3学习笔记(一)

淘声依旧 — Wed, 29 Oct 2008 11:24:00 GMT

下载最新hibernate的资源：http://www.hibernate.org/6.html 本文使用最新的 3.3.0 SP1 版本

所需jar包列表如下：

antlr-2.7.6.jar
commons-collections-3.1.jar
commons-logging-1.1.jar
dom4j-1.6.1.jar
ehcache-1.2.3.jar
ejb3-persistence.jar
hibernate3.jar
hibernate-annotations.jar
hibernate-commons-annotations.jar
hibernate-validator.jar
javassist-3.4.GA.jar
jta-1.1.jar
log4j.jar
mysql-connector-java-5.1.6-bin.jar
slf4j-api-1.4.2.jar
slf4j-log4j12.jar

hibernate.cfg.xml配置文件：

"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
com.mysql.jdbc.Driver
jdbc:mysql://localhost:3306/hb3demo
org.hibernate.dialect.MySQL5Dialect
root
root
50
30
true
true
org.hibernate.transaction.JDBCTransactionFactory
org.hibernate.cache.EhCacheProvider
true

log4j.properties

log4j.rootLogger=warn, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %c{1}:%L - %m%n

User.java

package com.hb3.pack_01.model;
public class User {
private Integer id;
private String name;
private Integer age;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
}

User.hbm.xml

"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

BusinessService.java

package com.hb3.pack_01;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import com.hb3.pack_01.model.User;
public class BusinessService {
public static void main(String[] args) {
Configuration config = new Configuration().configure();
SessionFactory sessionFactory = config.buildSessionFactory();
Session session = sessionFactory.openSession();
User user = new User();
user.setName("shenbin");
user.setAge(new Integer(28));
Transaction tx = session.beginTransaction();
session.save(user);
tx.commit();
session.close();
sessionFactory.close();
}
}

在MySQL数据库中新建数据库hb3demo，并执行如下DDL

CREATE TABLE user (
id INT(11) NOT NULL auto_increment PRIMARY KEY,
name VARCHAR(100) NOT NULL default '',
age INT
);

这样就可以使用ｈｉｂｅｒｎａｔｅ向数据库插入数据了。

淘声依旧 2008-10-29 19:24 发表评论