Java的Struts2框架配合Ext JS处理JSON数据的使用示例

最近尝试用extjs来展示树状菜单。着实花了一番功夫。树状菜单的菜单项需要动态加载，而目前版本的extjs中只支持json格式的数据。查了一些资 料，决定使用struts2的json-plugin。首先按照例子做了一个，但是结果就是不成功，界面上只出来了一个js中生成的root节点，不能加 载从后台生成的数据。研究后发现是数据格式有问题。使用json-plugin生成的数据格式如下：

{"cls":"folder","id":10,"leaf":false,"children":[{"cls":"file","id":11,"leaf":true,"children":null,"text":"s600"},{"cls":"file","id":12,"leaf":true,"children":null,"text":"slk200"}],"text":"benz"}

而extjs需要的数据格式如下：

[{"cls":"folder","id":10,"leaf":false,"children":[{"cls":"file","id":11,"leaf":true,"children":null,"text":"s600"},{"cls":"file","id":12,"leaf":true,"children":null,"text":"slk200"}],"text":"benz"}]

区别很小，就只相差最外面的两个方括号。但是少了这两个方括号，在json中，含义迥然不同，前者表示一个对象，而后者表示一个数组。而extjs中 tree的dataloader需要的数据必须是一个数组。而这样的数据格式是json-plugin自动生成的，无法改变。所以，我最后放弃了json -plugin，转而使用json-lib来解决这个问题。
1. 下载json-lib, http://json-lib.sourceforge.net/
2. lib目录下的jar文件清单：
commons-beanutils-1.7.0.jar
commons-collections-3.2.jar
commons-digester-1.6.jar
commons-lang-2.3.jar
commons-logging-1.1.jar
dom4j-1.6.1.jar
ezmorph-1.0.4.jar
freemarker-2.3.8.jar
javassist-3.8.1.jar
json-lib-2.2.1-jdk15.jar
log4j-1.2.13.jar
ognl-2.6.11.jar
struts2-core-2.0.11.jar
xml-apis-1.0.b2.jar
xwork-2.0.4.jar

首先配置web.xml

<?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">
 <welcome-file-list>
 <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
 <filter>
 <filter-name>struts2</filter-name>
 <filter-class>org.apache.struts2.dispatcher.filterdispatcher</filter-class>
 </filter>

 <filter-mapping>
 <filter-name>struts2</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>
</web-app>

然后是struts.xml

<?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>
 <constant name="struts.devmode" value="true"/>
 <constant name="struts.i18n.encoding" value="utf-8"/>
 <package name="person" extends="struts-default">
 <action name="menus" method="execute" class="com.lab.menuaction">
  <result>/menu.jsp</result>
 </action>
 </package>
</struts>

3. 树的节点模型（省略了getter，setter)

public class menu {
 private int id;
 private string text;
 private boolean leaf;
 private string cls;
 private list<menu> children;
}

4. action

package com.lab;

import java.util.arraylist;
import java.util.list;

import net.sf.json.jsonarray;

public class menuaction {
 private string menustring;
 
 private list<menu> menus;
 
 public string execute() {

 menus = new arraylist<menu>();
 
 menu benz = new menu();
 benz.settext("benz");
 benz.setcls("folder");
 benz.setleaf(false);
 benz.setid(10);
 menus.add(benz);
 
 list<menu> benzlist = new arraylist<menu>();
 benz.setchildren(benzlist);
 
 menu menu;
 menu = new menu();
 menu.settext("s600");
 menu.setcls("file");
 menu.setleaf(true);
 menu.setid(11);
 benzlist.add(menu);
 menu = new menu();
 menu.settext("slk200");
 menu.setcls("file");
 menu.setleaf(true);
 menu.setid(12);
 benzlist.add(menu);
 
 menu bmw = new menu();
 bmw.settext("bmw");
 bmw.setcls("folder");
 bmw.setleaf(false);
 bmw.setid(20);
 menus.add(bmw);
 
 list<menu> bmwlist = new arraylist<menu>();
 bmw.setchildren(bmwlist);
 
 menu = new menu();
 menu.settext("325i");
 menu.setcls("file");
 menu.setleaf(true);
 menu.setid(21);
 bmwlist.add(menu);
 
 menu = new menu();
 menu.settext("x5");
 menu.setcls("file");
 menu.setleaf(true);
 menu.setid(22);
 bmwlist.add(menu);
 
 jsonarray jsonobject = jsonarray.fromobject(menus);
 try {
  menustring = jsonobject.tostring();
 } catch (exception e) {
  menustring = "ss";
 }

 return "success";
 }

 public string getmenustring() {
 return menustring;
 }

 public void setmenustring(string menustring) {
 this.menustring = menustring;
 }
}

5. menu.jsp

<%@ taglib prefix="s" uri="/struts-tags" %>
<s:property value="menustring" escape="false"/>

6. html页面和js
我使用的就是extjs的example中的reorder.html和reorder.js，更改了reorder.js中treeloader的dataurl： menus.action

<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
<title>reorder treepanel</title>
<link rel="stylesheet" type="text/css" href="extjs/resources/css/ext-all.css" />

 <!-- gc -->
 <!-- libs -->
 <script type="text/javascript" src="extjs/adapter/ext/ext-base.js"></script>
 <!-- endlibs -->
 
 <script type="text/javascript" src="extjs/ext-all.js"></script>
<script type="text/javascript" src="reorder.js"></script>

<!-- common styles for the examples -->
<link rel="stylesheet" type="text/css" href="extjs/resources/css/example.css" />
</head>
<body>
<script type="text/javascript" src="../examples.js"></script><!-- examples -->
<h1>drag and drop ordering in a treepanel</h1>
<p>this example shows basic drag and drop node moving in a tree. in this implementation there are no restrictions and 
anything can be dropped anywhere except appending to nodes marked "leaf" (the files). <br></p>
<p>drag along the edge of the tree to trigger auto scrolling while performing a drag and drop.</p>
<p>in order to demonstrate drag and drop insertion points, sorting was <b>not</b> enabled.</p>
<p>the data for this tree is asynchronously loaded with a json treeloader.</p>
<p>the js is not minified so it is readable. see <a href="reorder.js">reorder.js</a>.</p>

<div id="tree-div" style="overflow:auto; height:300px;width:250px;border:1px solid #c3daf9;"></div>

</body>
</html>

js:

/*
 * ext js library 2.0.1
 * copyright(c) 2006-2008, ext js, llc.
 * [e-mail]
 *
 * http://extjs.com/license
 */

ext.onready(function(){
 // shorthand
 var tree = ext.tree;
 
 var tree = new tree.treepanel({
 el:'tree-div',
 autoscroll:true,
 animate:true,
 enabledd:true,
 containerscroll: true,
 loader: new tree.treeloader({
  dataurl:'http://localhost:8080/lab/menus.action'
 })
 });

 // set the root node
 var root = new tree.asynctreenode({
 text: 'ext js',
 draggable:false,
 id:'source'
 });
 tree.setrootnode(root);

 // render the tree
 tree.render();
 root.expand();
});

7.解析为list数据
代码如下：
extjs中的json数据

var combostore = new ext.data.store({ 
 proxy: new ext.data.httpproxy({ 
   url:'admingroup', //这里是struts请求到action 
   method:'post' //请求方式 
  }), 
 reader: new ext.data.jsonreader({  
  //总记录数 
   totalproperty: 'results', //总记录数 
   root: 'items', //记录集合 
   id:'roleid' 
  }, 
  ['roleid','rolename'] //显示的两个字段 
  ) 
 }); 

          
json数据内容

{"items":[{"password":"ahui","adminid":1,"role":{"rolename":"系统管理员","roleid":2,"sequence":"2","admin":null,"logoutmark":"否"},"adminname":"ahui","logout":"否"},
 {"password":"xiao","adminid":2,"role":{"rolename":"系统管理员","roleid":2,"sequence":"2","admin":null,"logoutmark":"否"},"adminname":"xiao","logout":"是"},"results":13}

 
 
下面是struts2里面的action代码 里面封装了exthelper工具类，里面有转换xml和json两种格式

public string findall() throws exception{ 
 
  httpservletrequest request = servletactioncontext.getrequest(); 
 
  httpservletresponse response = servletactioncontext.getresponse(); 
 
  list list = groupservice.getgroup(); //调用service里面的方法，把所有的数据都查询出来 
 
  string json = exthelper.getjsonfromlist(list);//把list转换为json格式的数据 
 
  response.setcontenttype("text/json;charset=utf-8");//设置数据到前台显示的字符编码，如果不转会有乱码 
 
  response.getwriter().write(json); 
 
  system.out.println(json); 
 
  return null; 
} 

解析json的方法有很多,所以是怎么方便怎么来,json自己的包里也可以进行转换,但如果项目中用的是struts2,直接用struts2提供的方法更方便。