Extjs示例中的静态加载如何换为动态加载？

Question

Extjs有这样一个例子，下面是加载数据代码，但这里使用的是静态数据，我想换为动态加载，但不知道怎么办。
ApiPanel = function() {
    ApiPanel.superclass.constructor.call(this, {
        id:'api-tree',
        region:'west',
        split:true,
        header: false,
        width: 280,
        minSize: 175,
        maxSize: 500,
        collapsible: true,
        margins:'0 0 5 5',
        cmargins:'0 0 0 0',
        rootVisible:true,
        lines:false,
        autoScroll:true,
        animCollapse:false,
        animate: false,
        collapseMode:'mini',
        loader: new Ext.tree.TreeLoader({
            preloadChildren: true,
            clearOnLoad: false
        }),
        root: new Ext.tree.AsyncTreeNode({
            text:'ROOT',
            id:'root',
            expanded:true,
            children:[Docs.classData]        }),
        collapseFirst:false
    });
    // no longer needed!
    //new Ext.tree.TreeSorter(this, {folderSort:true,leafAttr:'isClass'});    this.getSelectionModel().on('beforeselect', function(sm, node) {
        return node.isLeaf();
    });
};

Answer 1

从后台去数据；dataUrl: 'url.jsp',

Answer 2

能给多一些代码吗？
loader:new Ext.tree.TreeLoader({
                url:"tree/treedata"
            })
我这样改了以后可以取数据，但显示不了。

Answer 3

tree这样写：
xtype: "treepanel",
width: 130,
loader: new Ext.tree.TreeLoader({
    url: "",
    baseParams: {
        action: "GetTreeNode"
    }
}),
root: new Ext.tree.AsyncTreeNode({
    text: "全部",
    id: "0",
    expanded: true
})
后台返回代码格式：
[{
    "id": "2",
    "text": "123",
    "leaf": true,
    "icon": "Ext/resources/images/default/tree/folder.gif",
    "qtip": "123"
},
{
    "id": "3",
    "text": "456",
    "leaf": true,
    "icon": "Ext/resources/images/default/tree/folder.gif",
    "qtip": "456"
}]