Spring的构建系统以及依赖管理使用的是Apache Ivy，从源码包看出，也使用了Maven。

Maven确实是个好东西，好处不再多言，以后希望能进一步用好它。

二、新特性如下：

Spring Expression Language （Spring表达式语言）

IoC enhancements/Java based bean metadata （Ioc增强/基于Java的bean元数据）

General-purpose type conversion system and UI field formatting system （通用类型转换系统和UI字段格式化系统）

Object to XML mapping functionality (OXM) moved from Spring Web Services project （对象到XML映射功能从Spring Web Services项目移出）

Comprehensive REST support （广泛的REST支持）

@MVC additions （@MVC增强）

Declarative model validation （声明式模型验证）

Early support for Java EE 6 （提前对Java EE6提供支持）

Embedded database support （嵌入式数据库的支持）

三、针对Java 5的核心API升级

1、BeanFactory接口尽可能返回明确的bean实例，例如：

T getBean(String name, Class requiredType)

Map getBeansOfType(Class type)

Spring3对泛型的支持，又进了一步。个人建议泛型应该多用，有百利而无一害！

2、Spring的TaskExecutor接口现在继承自java.util.concurrent.Executor：

扩展的子接口AsyncTaskExecutor支持标准的具有返回结果Futures的Callables。

任务计划，个人还是更喜欢Quartz。

3、新的基于Java5的API和SPI转换器

无状态的ConversionService 和 Converters

取代标准的JDK PropertyEditors

类型化的ApplicationListener，这是一个实现“观察者设计模式”使用的事件监听器。

基于事件的编程模式，好处多多，在项目中应该考虑使用，基于事件、状态迁移的设计思路，有助于理清软件流程，和减少项目的耦合度。

四、Spring表达式语言

Spring表达式语言是一种从语法上和统一表达式语言（Unified EL）相类似的语言，但提供更多的重要功能。它可以在基于XML配置文件和基于注解的bean配置中使用，并作为基础为跨Spring portfolio平台使用表达式语言提供支持。

接下来，是一个表达式语言如何用于配置一个数据库安装中的属性的示例：

<bean class="mycompany.RewardsTestDatabase">
    <property name="databaseName"
        value="#{systemProperties.databaseName}"/>
    <property name="keyGenerator"
        value="#{strategyBean.databaseKeyGenerator}"/>
</bean>
如果你更愿意使用注解来配置你的组件，那么这种功能同样可用：

@Repository public class RewardsTestDatabase {
      @Value("#{systemProperties.databaseName}")
      public void setDatabaseName(String dbName) { … }
     
      @Value("#{strategyBean.databaseKeyGenerator}")
      public voidsetKeyGenerator(KeyGenerator kg) { … }
}

又多一种表达式语言，造轮子的运动还在继续中！

五、基于Java的bean元数据

JavaConfig项目中的一些核心特性已经集成到了Spring中来，这意味着如下这些特性现在已经可用了：

@Configuration

@Bean

@DependsOn

@Primary

@Lazy

@Import

@Value

又来一堆的注解，无语了，感觉还是配置文件方便！：（

这儿有一个例子，关于一个Java类如何使用新的JavaConfig特性提供基础的配置信息：

package org.example.config;

@Configuration
public class AppConfig {
    private @Value("#{jdbcProperties.url}") String jdbcUrl;
    private @Value("#{jdbcProperties.username}") String username;
    private @Value("#{jdbcProperties.password}") String password;

    @Bean
    public FooService fooService() {
        return new FooServiceImpl(fooRepository());
    }

    @Bean
    public FooRepository fooRepository() {
        return new HibernateFooRepository(sessionFactory());
    }

    @Bean
    public SessionFactory sessionFactory() {
        // wire up a session factory
        AnnotationSessionFactoryBean asFactoryBean =
            new AnnotationSessionFactoryBean();
        asFactoryBean.setDataSource(dataSource());
        // additional config
        return asFactoryBean.getObject();
    }

    @Bean
    public DataSource dataSource() {
        return new DriverManagerDataSource(jdbcUrl, username, password);
    }
}为了让这段代码开始生效，我们需要添加如下组件扫描入口到最小化的应用程序上下文配置文件中：

<context:component-scan base-package="org.example.config"/>
<util:properties id="jdbcProperties" location="classpath:org/example/config/jdbc.properties"/>

六、在组件中定义bean的元数据

感觉Spring提供了越来越多的注解、元数据，复杂性已经超出了当初带来的方便本身！

七、通用类型转换系统和UI字段格式化系统

Spring3加入了一个通用的类型转换系统，目前它被SpEL用作类型转换，并且可能被一个Spring容器使用，用于当绑定bean的属性值的时候进行类型转换。

另外，还增加了一个UI字段格式化系统，它提供了更简单的使用并且更强大的功能以替代UI环境下的JavaBean的PropertyEditors，例如在SpringMVC中。

这个特性要好好研究下，通用类型转换系统如果果如所言的话，带来的好处还是很多的。

八、数据层

对象到XML的映射功能已经从Spring Web Services项目移到了Spring框架核心中。它位于org.springframework.oxm包中。

OXM?研究下！时间真不够！

九、Web层

在Web层最激动人心的新特性莫过于新增的对构件REST风格的web服务和web应用的支持！另外，还新增加了一些任何web应用都可以使用的新的注解。

服务端对于REST风格的支持，是通过扩展既有的注解驱动的MVC web框架实现的。

客户端的支持则是RestTemplate类提供的。

无论服务端还是客户端REST功能，都是使用HttpConverter来简化对HTTP请求和应答过程中的对象到表现层的转换过程。

MarshallingHttpMessageConverter使用了上面提到的“对象到XML的映射机制”。

十、@MVC增强

新增了诸如@CookieValue 和 @RequestHeaders这样的注解等。

十一、声明式模型验证

支持JSR 303，使用Hibernate Validator作为实现。

十二、提前对Java EE6提供支持

提供了使用@Async注解对于异步方法调用的支持（或者EJB 3.1里的 @Asynchronous）

另外，新增对JSR 303, JSF 2.0, JPA 2.0等的支持。

十三、嵌入式数据库的支持

对于嵌入式的Java数据库引擎提供了广泛而方便的支持，诸如HSQL, H2, 以及Derby等。

这是不是代表一种潮流呢？数据库向越来越小型化发展，甚至小型化到嵌入式了，我认为这在桌面级应用上还是很有市场的。

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/abigfrog/archive/2009/10/30/4748685.aspx

HQL: Hibernate查询语言

Hibernate配备了一种非常强大的查询语言，这种语言看上去很像SQL。但是不要被语法结构上的相似所迷惑，HQL是非常有意识的被设计为完全面向对象的查询，它可以理解如继承、多态 和关联之类的概念。

from eg.Cat

from Cat

from Cat as cat

from Cat cat

from Formula, Parameter

from Formula as form, Parameter as param

from Cat as cat
inner join cat.mate as mate
left outer join cat.kittens as kitten

from Cat as cat left join cat.mate.kittens as kittens

from Formula form full join form.parameter param

from Cat as cat
join cat.mate as mate
left join cat.kittens as kitten

from Cat as cat
inner join fetch cat.mate
left join fetch cat.kittens

from Document fetch all properties order by name

from Document doc fetch all properties where lower(doc.name) like '%cats%'

select mate
from Cat as cat
inner join cat.mate as mate

select cat.mate from Cat cat

select cat.name from DomesticCat cat
where cat.name like 'fri%'

select cust.name.firstName from Customer as cust

select mother, offspr, mate.name
from DomesticCat as mother
inner join mother.mate as mate
left outer join mother.kittens as offspr

select new list(mother, offspr, mate.name)
from DomesticCat as mother
inner join mother.mate as mate
left outer join mother.kittens as offspr

select new Family(mother, mate, offspr)
from DomesticCat as mother
join mother.mate as mate
left join mother.kittens as offspr

select max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n
from Cat cat

select new map( max(bodyWeight) as max, min(bodyWeight) as min, count(*) as n )
from Cat cat

select avg(cat.weight), sum(cat.weight), max(cat.weight), count(cat)
from Cat cat

select cat.weight + sum(kitten.weight)
from Cat cat
join cat.kittens kitten
group by cat.id, cat.weight

select firstName||' '||initial||' '||upper(lastName) from Person

select distinct cat.name from Cat cat
select count(distinct cat.name), count(cat) from Cat cat

from Cat as cat

from java.lang.Object o

from Named n, Named m where n.name = m.name

from Cat where name='Fritz'

from Cat as cat where cat.name='Fritz'

select foo
from Foo foo, Bar bar
where foo.startDate = bar.date

from Cat cat where cat.mate.name is not null

from Foo foo
where foo.bar.baz.customer.address.city is not null

from Cat cat, Cat rival where cat.mate = rival.mate

select cat, mate
from Cat cat, Cat mate
where cat.mate = mate

from Cat as cat where cat.id = 123
from Cat as cat where cat.mate.id = 69

from bank.Person person
where person.id.country = 'AU'
and person.id.medicareNumber = 123456

from bank.Account account
where account.owner.id.country = 'AU'
and account.owner.id.medicareNumber = 123456

from Cat cat where cat.class = DomesticCat

store.owner.address.city    // 正确
store.owner.address         // 错误!

from AuditLog log, Payment payment
where log.item.class = 'Payment' and log.item.id = payment.id

from DomesticCat cat where cat.name between 'A' and 'B'

from DomesticCat cat where cat.name in ( 'Foo', 'Bar', 'Baz' )

from DomesticCat cat where cat.name not between 'A' and 'B'

from DomesticCat cat where cat.name not in ( 'Foo', 'Bar', 'Baz' )

<property name="hibernate.query.substitutions">true 1, false 0</property>

from Cat cat where cat.alive = true

from Cat cat where cat.kittens.size > 0

from Cat cat where size(cat.kittens) > 0

from Calendar cal where maxelement(cal.holidays) > current date

from Order order where maxindex(order.items) > 100

from Order order where minelement(order.items) > 10000

select mother from Cat as mother, Cat as kit
where kit in elements(foo.kittens)

select p from NameList list, Person p
where p.name = some elements(list.names)

from Cat cat where exists elements(cat.kittens)

from Player p where 3 > all elements(p.scores)

from Show show where 'fizard' in indices(show.acts)

from Order order where order.items[0].id = 1234

select person from Person person, Calendar calendar
where calendar.holidays['national day'] = person.birthDay
and person.nationality.calendar = calendar

select item from Item item, Order order
where order.items[ order.deliveredItemIndices[0] ] = item and order.id = 11

select item from Item item, Order order
where order.items[ maxindex(order.items) ] = item and order.id = 11

select item from Item item, Order order
where order.items[ size(order.items) - 1 ] = item

select item, index(item) from Order order
join order.items item
where index(item) < 5

from DomesticCat cat where upper(cat.name) like 'FRI%'

select cust
from Product prod,
Store store
inner join store.customers cust
where prod.name = 'widget'
and store.location.name in ( 'Melbourne', 'Sydney' )
and prod = all elements(cust.currentOrder.lineItems)

SELECT cust.name, cust.address, cust.phone, cust.id, cust.current_order
FROM customers cust,
stores store,
locations loc,
store_customers sc,
product prod
WHERE prod.name = 'widget'
AND store.loc_id = loc.id
AND loc.name IN ( 'Melbourne', 'Sydney' )
AND sc.store_id = store.id
AND sc.cust_id = cust.id
AND prod.id = ALL(
SELECT item.prod_id
FROM line_items item, orders o
WHERE item.order_id = o.id
AND cust.current_order = o.id
)

from DomesticCat cat
order by cat.name asc, cat.weight desc, cat.birthdate

select cat.color, sum(cat.weight), count(cat)
from Cat cat
group by cat.color

select foo.id, avg(name), max(name)
from Foo foo join foo.names name
group by foo.id

select cat.color, sum(cat.weight), count(cat)
from Cat cat
group by cat.color
having cat.color in (eg.Color.TABBY, eg.Color.BLACK)

select cat
from Cat cat
join cat.kittens kitten
group by cat
having avg(kitten.weight) > 100
order by count(kitten) asc, sum(kitten.weight) desc

本文转自:http://www.blogjava.net/xylz/

DWR作为Ajax远程调用的服务端得到了很多程序员的追捧，在DWR的2.x版本中已经集成了Guice的插件。

老套了，我们还是定义一个HelloWorld的服务吧，哎，就喜欢HelloWorld，不怕被别人骂！ 

1 public interface HelloWorld {
2 
3     String sayHello();
4 
5     Date getSystemDate();
6 }
7 

然后写一个简单的实现吧。 

 1 public class HelloWorldImpl implements HelloWorld {
 2 
 3     @Override
 4     public Date getSystemDate() {
 5         return new Date();
 6     }
 7 
 8     @Override
 9     public String sayHello() {
10         return "Hello, guice";
11     }
12 }
13 

然后是与dwr有关的东西了，我们写一个dwr的listener来注入我们的模块。 

 1 package cn.imxylz.study.guice.web.dwr;
 2 
 3 import org.directwebremoting.guice.DwrGuiceServletContextListener;
 4 
 5 /**
 6  * @author xylz (www.imxylz.cn)
 7  * @version $Rev: 105 $
 8  */
 9 public class MyDwrGuiceServletContextListener extends DwrGuiceServletContextListener{
10 
11     @Override
12     protected void configure() {
13         bindRemotedAs("helloworld", HelloWorld.class).to(HelloWorldImpl.class).asEagerSingleton();
14     }
15 }
16 

这里使用bindRemotedAs来将我们的服务开放出来供dwr远程调用。

剩下的就是修改web.xml，需要配置一个dwr的Servlet并且将我们的listener加入其中。看看全部的内容。 

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 3     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
 4     version="2.5">
 5 
 6     <display-name>guice-dwr</display-name>
 7     <description>xylz study project - guice</description>
 8 
 9     <listener>
10         <listener-class>cn.imxylz.study.guice.web.dwr.MyDwrGuiceServletContextListener
11         </listener-class>
12     </listener>
13     <servlet>
14         <servlet-name>dwr-invoker</servlet-name>
15         <servlet-class>org.directwebremoting.guice.DwrGuiceServlet</servlet-class>
16         <init-param>
17           <param-name>debug</param-name>
18           <param-value>true</param-value>
19         </init-param>
20     </servlet>
21     <servlet-mapping>
22         <servlet-name>dwr-invoker</servlet-name>
23         <url-pattern>/dwr/*</url-pattern>
24     </servlet-mapping>
25 
26 </web-app>
27 

非常简单，也非常简洁，其中DwrGuiceServlet的debug参数只是为了调试方便才开放的，实际中就不用写了。

好了，看看我们的效果。

 1 <html>
 2 <head><title>dwr - test (www.imxylz.cn) </title>
 3   <script type='text/javascript' src='/guice-dwr/dwr/interface/helloworld.js'></script>
 4   <script type='text/javascript' src='/guice-dwr/dwr/engine.js'></script>
 5   <script type='text/javascript' src='/guice-dwr/dwr/util.js'></script>
 6   <script type='text/javascript'>
 7     var showHello = function(data){
 8         dwr.util.setValue('result',dwr.util.toDescriptiveString(data,1));   
 9     }
10     var getSystemDate = function(data){
11         dwr.util.setValue('systime',dwr.util.toDescriptiveString(data,2));   
12     }
13   </script>
14   <style type='text/css'>
15     input.button { border: 1px outset; margin: 0px; padding: 0px; }
16     span { background: #ffffdd; white-space: pre; padding-left:20px;}
17   </style>
18 </head>
19 <body onload='dwr.util.useLoadingMessage()'>
20     <p>
21     <h2>Guice and DWR</h2>
22         <input class='button' type='button' value="Call HelloWorld 'sayHello' service" onclick="helloworld.sayHello(showHello)" />
23         <span id='result' ></span>
24     </p>
25     <p>
26         <input class='button' type='button' value="Call HelloWorld 'getSystemDate' service" onclick="helloworld.getSystemDate(getSystemDate)" />
27         <span id='systime' ></span>
28     </P>
29 </body>
30 </html>

我们通过两个按钮来获取我们的远程调用的结果。

Guice可真轻啊，所需的3个Jar包才不到600k。但缺点就是必须JDK1.5以上，像我们公司有几十个大大小小的Java项目，没有一个是1.5的，有点感慨啊。废话少说

IHelloService.java

package com.leo.service;
import com.google.inject.ImplementedBy;
import com.leo.service.impl.HelloServiceImpl;
/*
* 采用annotation进行接口与实现类之间的绑定
* 注意：接口与实现类之间绑定是必须的，如果只是单独一个类，没有接口，
* 那么Guice会隐式的自动帮你注入。并且接口此是不应该声明注入域范围的，
* 应该在其实现地方声明
*
*/
@ImplementedBy(HelloServiceImpl.class)
public interface IHelloService {
public String sayHello(String str);
}

package com.leo.service.impl;
import com.google.inject.Singleton;
import com.leo.service.IHelloService;
/*
* 这里如果默认不用annotation标注其作用域，或在自定义的module也不指定的话
* 默认的创建对象的方式是类似于Spring的prototype，在此处因为仅仅是一个stateless service
* 我们用@Singleton来标注它，更多的作用域可看Guice文档
*
* 注意：与标注@Singleton等效的工作也可以在自定义的module里来实现
*/
@Singleton
public class HelloServiceImpl implements IHelloService {
public String sayHello(String str) {
return new StringBuilder("Hello " + str + " !").toString();
}
}

struts.objectFactory = guice
#如果自已想实现Module接口，则下面注释请去掉
#guice.module=com.leo.module.MyModule
struts.action.extension=

package com.leo.action;
import com.google.inject.Inject;
import com.leo.service.IHelloService;
import com.opensymphony.xwork2.ActionSupport;
public class HelloAction extends ActionSupport {
private static final long serialVersionUID = -338076402728419581L;
/*
* 通过field字段进行注入，除此之外，还有construct, method注入均可
*/
@Inject
private IHelloService helloService;
private String message;
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public String execute() {
message = helloService.sayHello("leo");
return SUCCESS;
}
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<package name="default" extends="struts-default">
<action name="hello" class="com.leo.action.HelloAction">
<result>index.jsp</result>
</action>
</package>
</struts>

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<filter>
<filter-name>guice</filter-name>
<filter-class>
com.google.inject.servlet.GuiceFilter
</filter-class>
</filter>
<filter>
<filter-name>struts</filter-name>
<filter-class>
org.apache.struts2.dispatcher.FilterDispatcher
</filter-class>
</filter>
<filter-mapping>
<filter-name>guice</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>struts</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

package com.leo.module;
import com.google.inject.Binder;
import com.google.inject.Module;
import com.google.inject.Scopes;
import com.leo.service.IHelloService;
import com.leo.service.impl.HelloServiceImpl;
/*
* 如果你觉得Annotation有种支离破碎的感觉，别急，Guice还为你提供一种统一
* 注入管理的自定义实现。在本例中，先前的IHelloService, HelloServiceImpl
* 你现在可以完全将所有的Annotation去掉，然后实现Module接口的唯一一个方法
* 实现如下
*/
public class MyModule implements Module {
public void configure(Binder binder) {
/*
* 将接口IHelloService 与其实现HelloServiceImpl 绑定在一起 并且作用域为Scopes.SINGLETON
* 在这里有多种配置方法，但因为是入门实例，不想说的太复杂。其中如果不配置作用域，默认就是类似于Spring
* 的Scope="prototype"
*/
binder.bind(IHelloService.class).to(HelloServiceImpl.class).in(
Scopes.SINGLETON);
}
}

In this example, we will unmarshall the same XML document that we used in the previous article:

<?xml version="1.0"?>
<catalog library="somewhere">
<book>
<author>Author 1</author>
<title>Title 1</title>
</book>
<book>
<author>Author 2</author>
<title>His One Book</title>
</book>
<magazine>
<name>Mag Title 1</name>
<article page="5">
<headline>Some Headline</headline>
</article>
<article page="9">
<headline>Another Headline</headline>
</article>
</magazine>
<book>
<author>Author 2</author>
<title>His Other Book</title>
</book>
<magazine>
<name>Mag Title 2</name>
<article page="17">
<headline>Second Headline</headline>
</article>
</magazine>
</catalog>

The bean classes are also the same, except for one important change: In the previous article, I had declared these classes to have package scope -- primarily so that I could define all of them in the same source file! Using the Digester framework, this is no longer possible; the classes need to be declared as public (as is required for classes conforming to the JavaBeans specification):

import java.util.Vector;
public class Catalog {
private Vector books;
private Vector magazines;
public Catalog() {
books = new Vector();
magazines = new Vector();
}
public void addBook( Book rhs ) {
books.addElement( rhs );
}
public void addMagazine( Magazine rhs ) {
magazines.addElement( rhs );
}
public String toString() {
String newline = System.getProperty( "line.separator" );
StringBuffer buf = new StringBuffer();
buf.append( "--- Books ---" ).append( newline );
for( int i=0; i<books.size(); i++ ){
buf.append( books.elementAt(i) ).append( newline );
}
buf.append( "--- Magazines ---" ).append( newline );
for( int i=0; i<magazines.size(); i++ ){
buf.append( magazines.elementAt(i) ).append( newline );
}
return buf.toString();
}
}

public class Book {
private String author;
private String title;
public Book() {}
public void setAuthor( String rhs ) { author = rhs; }
public void setTitle(  String rhs ) { title  = rhs; }
public String toString() {
return "Book: Author='" + author + "' Title='" + title + "'";
}
}

import java.util.Vector;
public class Magazine {
private String name;
private Vector articles;
public Magazine() {
articles = new Vector();
}
public void setName( String rhs ) { name = rhs; }
public void addArticle( Article a ) {
articles.addElement( a );
}
public String toString() {
StringBuffer buf = new StringBuffer( "Magazine: Name='" + name + "' ");
for( int i=0; i<articles.size(); i++ ){
buf.append( articles.elementAt(i).toString() );
}
return buf.toString();
}
}

public class Article {
private String headline;
private String page;
public Article() {}
public void setHeadline( String rhs ) { headline = rhs; }
public void setPage(     String rhs ) { page     = rhs; }
public String toString() {
return "Article: Headline='" + headline + "' on page='" + page + "' ";
}

}

























import org.apache.commons.digester.*;
import java.io.*;
import java.util.*;
public class DigesterDriver {
public static void main( String[] args ) {
try {
Digester digester = new Digester();
digester.setValidating( false );
digester.addObjectCreate( "catalog", Catalog.class );
digester.addObjectCreate( "catalog/book", Book.class );
digester.addBeanPropertySetter( "catalog/book/author", "author" );
digester.addBeanPropertySetter( "catalog/book/title", "title" );
digester.addSetNext( "catalog/book", "addBook" );
digester.addObjectCreate( "catalog/magazine", Magazine.class );
digester.addBeanPropertySetter( "catalog/magazine/name", "name" );
digester.addObjectCreate( "catalog/magazine/article", Article.class );
digester.addSetProperties( "catalog/magazine/article", "page", "page" );
digester.addBeanPropertySetter( "catalog/magazine/article/headline" );
digester.addSetNext( "catalog/magazine/article", "addArticle" );
digester.addSetNext( "catalog/magazine", "addMagazine" );
File input = new File( args[0] );
Catalog c = (Catalog)digester.parse( input );
System.out.println( c.toString() );
} catch( Exception exc ) {
exc.printStackTrace();
}
}
}
After instantiating the Digester, we specify that it should not validate the XML document against a DTD -- because we did not define one for our simple Catalog document. Then we specify the patterns and the associated rules: the ObjectCreateRule creates an instance of the specified class and pushes it onto the parse stack. The SetPropertiesRule sets a bean property to the value of an XML attribute of the current element -- the first argument to the rule is the name of the attribute, the second, the name of the property. 
Whereas SetPropertiesRule takes the value from an attribute, BeanPropertySetterRule takes the value from the raw character data nested inside of the current element. It is not necessary to specify the name of the property to set when using BeanPropertySetterRule: it defaults to the name of the current XML element. In the example above, this default is being used in the rule definition matching the catalog/magazine/article/headline pattern. Finally, the SetNextRule pops the object on top of the parse stack and passes it to the named method on the object below it -- it is commonly used to insert a finished bean into its parent.
Note that it is possible to register several rules for the same pattern. If this occurs, the rules are executed in the order in which they are added to the Digester -- for instance, to deal with the <article> element, found at catalog/magazine/article, we first create the appropriate article bean, then set the page property, and finally pop the completed article bean and insert it into its magazine parent.
Invoking Arbitrary Functions
It is not only possible to set bean properties, but to invoke arbitrary methods on objects in the stack. This is accomplished using the CallMethodRule to specify the method name and, optionally, the number and type of arguments passed to it. Subsequent specifications of the CallParamRule define the parameter values to be passed to the invoked functions. The values can be taken either from named attributes of the current XML element, or from the raw character data contained by the current element. For instance, rather than using the BeanPropertySetterRule in the DigesterDriver implementation above, we could have achieved the same effect by calling the property setter explicitly, and passing the data as parameter:
   digester.addCallMethod( "catalog/book/author", "setAuthor", 1 );
digester.addCallParam( "catalog/book/author", 0 );
The first line gives the name of the method to call (setAuthor()), and the expected number of parameters (1). The second line says to take the value of the function parameter from the character data contained in the <author> element and pass it as first element in the array of arguments (i.e., the array element with index 0). Had we also specified an attribute name (e.g., digester.addCallParam( "catalog/book/author", 0, "author" );), the value would have been taken from the respective attribute of the current element instead.
One important caveat: confusingly, digester.addCallMethod( "pattern", "methodName", 0 ); does not specify a call to a method taking no arguments -- instead, it specifies a call to a method taking one argument, the value of which is taken from the character data of the current XML element! We therefore have yet another way to implement a replacement for BeanPropertySetterRule:
   digester.addCallMethod( "catalog/book/author", "setAuthor", 0 );
 
To call a method that truly takes no parameters, use digester.addCallMethod( "pattern", "methodName" );.








Summary of Standard Rules




 



Below are brief descriptions of all of the standard rules.
Creational

    

    
ObjectCreateRule: Creates an object of the specified class using its default constructor and pushes it onto the stack; it is popped when the element completes. The class to instantiate can be given through a class object or the fully-qualified class name.
    

    
FactoryCreateRule: Creates an object using a specified factory class and pushes it onto the stack. This can be useful for classes that do not provide a default constructor. The factory class must implement the org.apache.commons.digester.ObjectCreationFactory interface.
    

Property Setters

    

    
SetPropertiesRule: Sets one or several named properties in the top-level bean using the values of named XML element attributes. Attribute names and property names are passed to this rule in String[] arrays. (Typically used to handle XML constructs like <article page="10">.)
    

    
BeanPropertySetterRule: Sets a named property on the top-level bean to the character data enclosed by the current XML element. (Example: <page>10</page>.)
    

    
SetPropertyRule: Sets a property on the top-level bean. Both the property name, as well as the value to which this property will be set, are given as attributes to the current XML element. (Example: <article key="page" value="10" />.)
    

Parent/Child Management

    

    
SetNextRule: Pops the object on top of the stack and passes it to a named method on the object immediately below. Typically used to insert a completed bean into its parent.
    

    
SetTopRule: Passes the second-to-top object on the stack to the top-level object. This is useful if the child object exposes a setParent method, rather than the other way around.
    

    
SetRootRule: Calls a method on the object at the bottom of the stack, passing the object on top of the stack as argument. 
    

Arbitrary Method Calls

    

    
CallMethodRule: Calls an arbitrary named method on the top-level bean. The method may take an arbitrary set of parameters. The values of the parameters are given by subsequent applications of the CallParamRule. 
    

    
CallParamRule: Represents the value of a method parameter. The value of the parameter is either taken from a named XML element attribute, or from the raw character data enclosed by the current element. This rule requires that its position on the parameter list is specified by an integer index.
    

Specifying Rules in XML: Using the xmlrules Package


    

        

            

            
Related Reading
             
            
Programming Jakarta Struts

            By Chuck Cavaness 
            

            
        
    


So far, we have specified the patterns and rules programmatically at compile time. While conceptually simple and straightforward, this feels a bit odd: the entire framework is about recognizing and handling structure and data at run time, but here we go fixing the behavior at compile time! Large numbers of fixed strings in source code typically indicate that something is being configured (rather than programmed), which could be (and probably should be) done at run time instead.
The org.apache.commons.digester.xmlrules package addresses this issue. It provides the DigesterLoader class, which reads the pattern/rule-pairs from an XML document and returns a digester already configured accordingly. The XML document configuring the Digester must comply with the digester-rules.dtd, which is part of the xmlrules package.
Below is the contents of the configuration file (named rules.xml) for the example application. I want to point out several things here. 
Patterns can be specified in two different ways: either as attributes to each XML element representing a rule, or using the <pattern> element. The pattern defined by the latter is valid for all contained rule elements. Both ways can be mixed, and <pattern> elements can be nested -- in either case, the pattern defined by the child element is appended to the pattern defined in the enclosing <pattern> element.
The <alias> element is used with the <set-properties-rule> to map an XML attribute to a bean property.
Finally, using the current release of the Digester package, it is not possible to specify the BeanPropertySetterRule in the configuration file. Instead, we are using the CallMethodRule to achieve the same effect, as explained above.
<?xml version="1.0"?>
<digester-rules>
<object-create-rule pattern="catalog" classname="Catalog" />
<set-properties-rule pattern="catalog" >
<alias attr-name="library" prop-name="library" />
</set-properties-rule>
<pattern value="catalog/book">
<object-create-rule classname="Book" />
<call-method-rule pattern="author" methodname="setAuthor"
paramcount="0" />
<call-method-rule pattern="title" methodname="setTitle"
paramcount="0" />
<set-next-rule methodname="addBook" />
</pattern>
<pattern value="catalog/magazine">
<object-create-rule classname="Magazine" />
<call-method-rule pattern="name" methodname="setName" paramcount="0" />
<pattern value="article">
<object-create-rule classname="Article" />
<set-properties-rule>
<alias attr-name="page" prop-name="page" />
</set-properties-rule>
<call-method-rule pattern="headline" methodname="setHeadline"
paramcount="0" />
<set-next-rule methodname="addArticle" />
</pattern>
<set-next-rule methodname="addMagazine" />
</pattern>
</digester-rules>
Since all the actual work has now been delegated to the Digester and DigesterLoader classes, the driver class itself becomes trivially simple. To run it, specify the catalog document as the first command line argument, and the rules.xml file as the second. (Confusingly, the DigesterLoader will not read the rules.xml file from a File or an org.xml.sax.InputSource, but requires a URL -- the File reference in the code below is therefore transformed into an equivalent URL.)
import org.apache.commons.digester.*;
import org.apache.commons.digester.xmlrules.*;
import java.io.*;
import java.util.*;
public class XmlRulesDriver {
public static void main( String[] args ) {
try {
File input = new File( args[0] );
File rules = new File( args[1] );
Digester digester = DigesterLoader.createDigester( rules.toURL() );
Catalog catalog = (Catalog)digester.parse( input );
System.out.println( catalog.toString() );
} catch( Exception exc ) {
exc.printStackTrace();
}
}
}
Conclusion
This concludes our brief overview of the Jakarta Commons Digester package. Of course, there is more. One topic ignored in this introduction are XML namespaces: Digester allows you to specify rules that only act on elements defined within a certain namespace.
We mentioned briefly the possibility of developing custom rules, by extending the Rule class. The Digester class exposes the customary push(), peek(), and pop() methods, giving the individual developer freedom to manipulate the parse stack directly.
Lastly, note that there is an additional package providing a Digester implementation which deals with RSS (Rich-Site-Summary)-formatted newsfeeds. The Javadoc tells the full story.
References

    
Jakarta Commons Digester Homepage
    
"Simple XML Parsing with SAX and DOM"
    
Jakarta Struts Homepage
    
"Java & XML Data Binding" -- XML Data Binding addresses the general problem of making XML data available in applications.
    
Programming Jakarta Struts -- the upcoming book on Jakarta Struts at O'Reilly. 

Philipp K. Janert is a software project consultant, server programmer, and architect. 

1.属性的动态getter,setter

BeanUtils.getProperty(myBean,"code");

BeanUtils.getProperty(orderBean, "address.city");

BeanUtils.getProperty(orderBean, "customers[1].name");

2.beanCompartor 动态排序

List peoples = ...; // Person对象的列表Collections.sort(peoples, new BeanComparator("age"));

如果要支持多个属性的复合排序，如"Order By lastName,firstName"

ArrayList sortFields = new ArrayList();sortFields.add(new BeanComparator("lastName"));

sortFields.add(new BeanComparator("firstName"));

ComparatorChain multiSort = new ComparatorChain(sortFields);

Collections.sort(rows,multiSort);

其中ComparatorChain属于jakata commons-collections包。
如果age属性不是普通类型，构造函数需要再传入一个comparator对象为age变量排序。
另外, BeanCompartor本身的ComparebleComparator, 遇到属性为null就会抛出异常, 也不能设定升序还是降序。
这个时候又要借助commons-collections包的ComparatorUtils.

   Comparator mycmp = ComparableComparator.getInstance();
   mycmp = ComparatorUtils.nullLowComparator(mycmp);  //允许null
   mycmp = ComparatorUtils.reversedComparator(mycmp); //逆序
   Comparator cmp = new BeanComparator(sortColumn, mycmp);

   经常要从request,resultSet等对象取出值来赋入bean中，下面的代码谁都写腻了，如果不用MVC框架的绑定功能的话。

   String a = request.getParameter("a");   bean.setA(a);   String b = ....

不妨写一个Binder:

     MyBean bean = ...;    HashMap map = new HashMap();    Enumeration names = request.getParameterNames();    while (names.hasMoreElements())    {      String name = (String) names.nextElement();      map.put(name, request.getParameterValues(name));    }    BeanUtils.populate(bean, map);

    其中BeanUtils的populate方法或者getProperty,setProperty方法其实都会调用convert进行转换。
    但Converter只支持一些基本的类型，甚至连java.util.Date类型也不支持。而且它比较笨的一个地方是当遇到不认识的类型时，居然会抛出异常来。
    对于Date类型，我参考它的sqldate类型实现了一个Converter,而且添加了一个设置日期格式的函数。
要把这个Converter注册，需要如下语句：

    ConvertUtilsBean convertUtils = new ConvertUtilsBean();

    DateConverter dateConverter = new DateConverter();

    convertUtils.register(dateConverter,Date.class);







//因为要注册converter,所以不能再使用BeanUtils的静态方法了，必须创建BeanUtilsBean实例

BeanUtilsBean beanUtils = new BeanUtilsBean(convertUtils,new PropertyUtilsBean());

beanUtils.setProperty(bean, name, value);

     public static Class getPropertyType(Object bean, String name)

      public static Object invokeConstructor(Class klass, Object arg)

4.4 MethodUtils，动态调用方法

    MethodUtils.invokeMethod(bean, methodName, parameter);

1.BeanUtils基本用法：