BlogJava-pear-随笔分类-心得体会

伤心太平洋，左连接和内联的区别

pear — Thu, 14 Dec 2006 12:47:00 GMT

INNER: 指定返回所有相匹配的行对。废弃两个表中不匹配的行。如果未指定联接类型，则这是默认设置。
LEFT [OUTER]: 指定除所有由内联接返回的行外，所有来自左表的不符合指定条件的行也包含在结果集内。来自左表的输出列设置为 NULL。
RIGHT [OUTER]: 指定除所有由内联接返回的行外，所有来自右表的不符合指定条件的行也包含在结果集内。来自右表的输出列设置为 NULL。
FULL [OUTER]: 如果来自左表或右表的某行与选择准则不匹配，则指定在结果集内包含该行，并且将与另一个表对应的输出列设置为 NULL。除此之外，结果集中还包含通常由内联接返回的所有行。
: 指定联接提示或执行算法。如果指定了，也必须明确指定 INNER、LEFT、RIGHT 或 FULL。有关联接提示的更多信息，请参见 FROM。
JOIN: 表示联接所指定的表或视图。

pear 2006-12-14 20:47 发表评论

重新学习 Hibernate fetch lazy cascade inverse 关键字

pear — Sun, 05 Nov 2006 12:04:00 GMT

Hibernate最让人头大的就是对集合的加载形式。
书看了N次了，还是没有真正理解Hibernate。所以下午专门做了下测试，对配置文件的意思加深了认识。

假设有两个表，Photos(一） --- picture(多）Photo包含picture集合

结论1： HQL代码 > fetch（配置） > lazy （配置）
结论2：默认 lazy="true"
结论3： fetch 和 lazy 主要是用来级联查询的，   而 cascade 和 inverse 主要是用来级联插入和修改的
结论4：如果你是用spring来帮你管理你的session, 并且是自动提交，延迟加载就等于没加载~_~(当然
                除非你手动重新打开session然后手动Hibernate.initialize(set);然后关闭session.
结论5:     cascade主要是简化了在代码中的级联更新和删除。
j结论6：老爸可以有多个孩子，一个孩子不能有多个老爸，而且老爸说的算, 孩子围着老爸转。
               所以Photos老爸要有权力所以 cascade 这个关键子都是送给老爸的，也就是级联更新，
               老爸改姓了，儿子也得跟着改，呵呵。“不然，就没有零花钱咯”。
                而Picture儿子整体挨骂，但是还是要维护父子之间良好的关系，对老爸百依百顺，所
               以老爸就说，儿子，“关系，由你来维护（inverse="true") ，不然就不给零花钱。呵。”。







测试代码：

   Photos p = ps.getById(1);
  Set set = p.getPictures();
  for(Picture pic : set){
   System.out.println(pic.getId());
  }

配置文件的一部分：







测试过程会对配置文件不断修改：并且从来不曾手动重新打开session

测试结构：

当配置条件为 lazy=true 一句查询测试代码中没有调用getPicture() 正常
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

lazy=true 一句查询有getPicture()
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

lazy=true 一句查询有getPicture() 并且访问了里面的元数Picture 且有异常抛出
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

lazy="false" 两句查询肯定没问题，因为全部数据都个查了出来所以怎么调用都正常
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?
Hibernate: select pictures0_.photosid as photosid1_, pictures0_.id as id1_, pictures0_.id as id2_0_, pictures0_.photosid as photosid2_0_, pictures0_.name as name2_0_, pictures0_.clicked as clicked2_0_, pictures0_.uploaddate as uploaddate2_0_, pictures0_.size as size2_0_, pictures0_.description as descript7_2_0_, pictures0_.uri as uri2_0_ from super.picture pictures0_ where pictures0_.photosid=?

fetch="join" 一句查询效果＝＝ lazy="false" 呵呵，哪个效率高，我就不知道了。。。。。。。。。。。
Hibernate: select photos0_.id as id0_1_, photos0_.userid as userid0_1_, photos0_.typeid as typeid0_1_, photos0_.name as name0_1_, photos0_.createtime as createtime0_1_, photos0_.description as descript6_0_1_, photos0_.faceid as faceid0_1_, photos0_.uri as uri0_1_, pictures1_.photosid as photosid3_, pictures1_.id as id3_, pictures1_.id as id2_0_, pictures1_.photosid as photosid2_0_, pictures1_.name as name2_0_, pictures1_.clicked as clicked2_0_, pictures1_.uploaddate as uploaddate2_0_, pictures1_.size as size2_0_, pictures1_.description as descript7_2_0_, pictures1_.uri as uri2_0_ from super.photos photos0_ left outer join super.picture pictures1_ on photos0_.id=pictures1_.photosid where photos0_.id=?

不加fetch＝"join" 一句查询没有getPicture() 正常
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

不加fetch＝"join" 一句查询有getPicture() 正常
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

不加fetch＝"join" 一句查询有getPicture() 并且访问里面的元素Picture的ID 有异常抛出
Hibernate: select photos0_.id as id0_0_, photos0_.userid as userid0_0_, photos0_.typeid as typeid0_0_, photos0_.name as name0_0_, photos0_.createtime as createtime0_0_, photos0_.description as descript6_0_0_, photos0_.faceid as faceid0_0_, photos0_.uri as uri0_0_ from super.photos photos0_ where photos0_.id=?

来个两兵交战 fetch="join" lazy="true" 呵呵结果，一句查询，结构正常所以就当lazy不存在好了。看来fetch 是老大。、、、、、、、、、、、、、
Hibernate: select photos0_.id as id0_1_, photos0_.userid as userid0_1_, photos0_.typeid as typeid0_1_, photos0_.name as name0_1_, photos0_.createtime as createtime0_1_, photos0_.description as descript6_0_1_, photos0_.faceid as faceid0_1_, photos0_.uri as uri0_1_, pictures1_.photosid as photosid3_, pictures1_.id as id3_, pictures1_.id as id2_0_, pictures1_.photosid as photosid2_0_, pictures1_.name as name2_0_, pictures1_.clicked as clicked2_0_, pictures1_.uploaddate as uploaddate2_0_, pictures1_.size as size2_0_, pictures1_.description as descript7_2_0_, pictures1_.uri as uri2_0_ from super.photos photos0_ left outer join super.picture pictures1_ on photos0_.id=pictures1_.photosid where photos0_.id=?

pear 2006-11-05 20:04 发表评论

js 天气预报，蒙了我好久。

pear — Fri, 03 Nov 2006 08:07:00 GMT

1。代码

http://minisite.qq.com/Weather/news_new.html" allowTransparency="true">

http://weather.265.com/weather.htm" width="168" height="54" frameborder="no" border="0" marginwidth="0" marginheight="0" scrolling="no">

http://weather.qq.com/24.htm">>

http://appnews.qq.com/cgi-bin/news_weather_search?city=广州" allowTransparency="true">

http://news.sina.com.cn/iframe/weather/440101.html">>

效果如下：

pear 2006-11-03 16:07 发表评论

用Sun creator创建的 jsf 项目部署到其他服务器的问题：

pear — Mon, 02 Oct 2006 02:59:00 GMT

用Sun creator创建的 jsf 项目部署到其他服务器的问题：

对jsf项目的支持，sun creator 无疑给人一种耳目一新的感觉：
他对可视化开发的支持真的开始可以和.Net较劲了。

但是 creator 有个问题就是可以把项目部署到 sun app server的项目部署到其他服务器老是出同样的问题：

下面总结一下：

步骤一: 把项目导出成 *.war文件
步骤二: 把*.war拷贝到其他服务器的部署目录
比如 tomcat/resin 的 webapp下
步骤三: 运行服务器(tomcat/resin) 问题来了,出现异常
[10:41:34.828] java.lang.NullPointerException
[10:41:34.828] at javax.faces.webapp.FacesServlet.init(FacesServlet.java:144)
[10:41:34.828] at com.caucho.server.dispatch.ServletConfigImpl.createServletImpl(ServletConfigImpl.java:646)
[10:41:34.828] at com.caucho.server.dispatch.ServletConfigImpl.createServlet(ServletConfigImpl.java:587)

看到这个"FacesServlet.java:144" 开始我怀疑是sun 的包的问题, 网上google和baidu了一下,没搜到相关问题的解决办法.
    最后在一个朋友的帮助下在web.xml文件里加了个Listener:

        com.sun.faces.config.ConfigureListener

嘿,还真行.

心得如下:
     在用workshop或者myeclipse用myfaces包建jsf项目时,我们不会碰到类似的问题.
因为工具已经在web.xml里面加了listener:


  org.apache.myfaces.webapp.StartupServletContextListener

但是如果用这些工具用 sun jsf 包时就要手动listerner.(如:步骤三)

给大家个连接: sun creator的教程,从这里开始学jsf感觉比较全面:
http://gceclub.sun.com.cn/prodtech/javatools/jscreator/learning/tutorials/index.html

pear 2006-10-02 10:59 发表评论

BBS中的一个查询问题（原创）

pear — Thu, 28 Sep 2006 10:49:00 GMT

问题：
在BBS中，content 和 review 两张表，其中content 记录的是帖子信息（topic_id,topic_title,topic_content等字段），review 表中记录的是回帖的信息，(review_id,topic_id等字段)在求一SQL语句，其中topic_id和review_id都是自动增加，现在要求查询出有最新回复的帖子的信息，同时要求有多个回复的一个帖子的主题只能显示一次，能用一个SQL语句搞定吗？数据库是MYSQL 求高手指点下

回答：
select t.id,t.title,t.content,r.newposttime from topic as t inner join (select max(posttime) as newposttime, topicid from review group by topicid) as r on t.id=r.topicid

//测试
create table topic(
id int primary key identity(1,1),
title varchar(128),
content text
)

insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')
insert into topic(title,content) values('title1','content1')

create table review(
id int primary key identity(1,1),
topicid int references topic(id),
content text,
posttime datetime default getdate()
)

insert into review(topicid,content) values(1,'reice1')
insert into review(topicid,content) values(1,'reice1')
insert into review(topicid,content) values(2,'reice1')
insert into review(topicid,content) values(2,'reice1')
insert into review(topicid,content) values(2,'reice1')
insert into review(topicid,content) values(3,'reice1')
insert into review(topicid,content) values(3,'reice1')
insert into review(topicid,content) values(3,'reice1')
insert into review(topicid,content) values(3,'reice1')
insert into review(topicid,content) values(4,'reice1')

select t.id,t.title,t.content,r.newposttime from topic as t inner join (select max(posttime) as newposttime, topicid from review group by topicid) as r on t.id=r.topicid

这些是测试数据,sqlserver2000测试通过

pear 2006-09-28 18:49 发表评论

AJAX传参从失败到成功小结:

pear — Sun, 13 Aug 2006 09:36:00 GMT

AJAX传参从失败到成功小结:

看了AJAX基础教程,感觉不错,但是在向服务器传递参数的时候总是会有让我感到苦恼的问题,
比如下面的代码:

在服务端的CountServlet的doGet()方法在多次请求之间只会被调用一次,痛苦!!!(难道是异步的问题...)

于是我又改了一下xmlHttp的open方法的参数如下,
xmlHttp.open("POST","/CountServlet,true)
xmlHttp.send("Sid="+Sid);
结果在服务器端的doPost()方法在每次请求都会被正常调用,但是,request.getPrameter("Sid")方法就是怎么也获得不到参数Sid,

在高手的帮助下,我又再次改了代码,如下:
xmlHttp.open("POST","/CountServlet?Sid="+Sid,false);
xmlHttp.send(null);
嘿,还真的,牙好,胃口就好,入口见效,doPost()方法能正常被调用,参数也传得到,具体是什么原因,我还在学习之中...

8.19日加：
解决办法：
除了高手回复的方法,还有一种解决办法就是:
xmlHttp.open("GET","/CountServlet?Sid="+Sid+"&timeStamp="+new Date().getTime(),false);
xmlHttp.send(null);
同样是解决缓存的问题..

pear 2006-08-13 17:36 发表评论

ServiceLocator 中一般包含static方法

pear — Mon, 10 Jul 2006 06:53:00 GMT

1。ServiceLocator 中一般包含static方法
2。ServiceLocator角色如果让TopBaseAction承担（可以非静态，也很方便）
3。ServiceLocator的角色和SessionFactory有些类似（都是用工厂模式）

10月5日，今天玩了一下把 Service层的实力注入到Action里面,我的ServiceLocator类也终于可以睡觉去了.

pear 2006-07-10 14:53 发表评论

JavaMail中文附件处理(转载)

pear — Fri, 16 Jun 2006 12:12:00 GMT

摘要: //SendMail.java import javax.mail. * ; import javax.mail.internet. * ... 阅读全文

pear 2006-06-16 20:12 发表评论