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.
 * licensing@extjs.com
 *
 * 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。