Extjs Tree + JSON + Struts2

最近嘗試用extjs來展示樹狀菜單。着實花了一番功夫。樹狀菜單的菜單項需要動態加載，而目前版本的extjs中只支持JSON格式的數據。查了一些資料，決定使用struts2的json-plugin。首先按照例子做了一個，但是結果就是不成功，界面上只出來了一個js中生成的root節點，不能加載從後臺生成的數據。研究後發現是數據格式有問題。使用json-plugin生成的數據格式如下：
{"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需要的數據格式如下：
[{"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"}]
區別很小，就只相差最外面的兩個方括號。但是少了這兩個方括號，在json中，含義迥然不同，前者表示一個對象，而後者表示一個數組。而extjs中 tree的dataloader需要的數據必須是一個數組。而這樣的數據格式是json-plugin自動生成的，無法改變。所以，我最後放棄了json -plugin，轉而使用json-lib來解決這個問題。
1. 下載json-lib, http://json-lib.sourceforge.net/
2. lib目錄下的jar文件清單：
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
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>

然後是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. 樹的節點模型（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頁面和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" />

    
     
     <script type="text/javascript" src="extjs/adapter/ext/ext-base.js"></script>
     

    <script type="text/javascript" src="extjs/ext-all.js"></script>
<script type="text/javascript" src="reorder.js"></script>


<link rel="stylesheet" type="text/css" href="extjs/resources/css/example.css" />
</head>
<body>
<script type="text/javascript" src="../examples.js"></script>
<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.
* [email protected]
*
* 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();
});