解析jquery easyui tree异步加载子节点问题

<ul id="tt"></ul>

$('#tt').tree({
  url:'/demo2/node/getNodes'  // The url will be mapped to NodeController class and getNodes method
});

@Table(name="nodes")
public class Node extends ActiveRecordBase{
  @Id public Integer id;
  @Column public Integer parentId;
  @Column public String name;
 
  public boolean hasChildren() throws Exception{
    long count = count(Node.class, "parentId=?", new Object[]{id});
    return count > 0;
  }
}

public class NodeController extends ApplicationController{
  /**
   * get nodes, if the 'id' parameter equals 0 then load the first level nodes,
   * otherwise load the children nodes
   * @param id the parent node id value
   * @return the tree required node json format
   * @throws Exception
   */
  public View getNodes(int id) throws Exception{
    List<Node> nodes = null;
 
    if (id == 0){  // return the first level nodes
      nodes = Node.findAll(Node.class, "parentId=0 or parentId is null", null);
    } else {  // return the children nodes
      nodes = Node.findAll(Node.class, "parentId=?", new Object[]{id});
    }
 
    List<Map<String,Object>> items = new ArrayList<Map<String,Object>>();
    for(Node node: nodes){
      Map<String,Object> item = new HashMap<String,Object>();
      item.put("id", node.id);
      item.put("text", node.name);
 
      // the node has children, 
      // set the state to 'closed' so the node can asynchronous load children nodes 
      if (node.hasChildren()){
        item.put("state", "closed");
      }
      items.add(item);
    }
 
    return new JsonView(items);
  }
}

$('#tt').tree({
　　method:"POST",
  url:'/demo2/node/getNodes'  // The url will be mapped to NodeController class and getNodes method
});