为Extjs 树提供数据的递归算法

（转自：http://emlyn1180.iteye.com/blog/315334 ）

首先先建立Node模型

public class Node {private int id;private int parentId;Node(){}Node(int id,int parentId){this.id=id;this.parentId = parentId;}public int getId() {return id;}public void setId(int id) {this.id = id;}public int getParentId() {return parentId;}public void setParentId(int parentId) {this.parentId = parentId;}}

下面这个类先手工建立List，在实际应用中是从数据库读取List，然后再Main方法里调用递归方法，得到Json字符串 

import java.util.ArrayList;import java.util.Iterator;import java.util.List;public class Recursion {List nodeList =new ArrayList();Recursion(){//构造方法里初始化模拟ListNode node1 = new Node(1,0);          Node node2 = new Node(2,1);          Node node3 = new Node(3,1);          Node node4 = new Node(4,2);          Node node5 = new Node(5,2);          Node node6 = new Node(6,2);          Node node7 = new Node(7,6);          Node node8 = new Node(8,6);                    nodeList.add(node1);          nodeList.add(node2);          nodeList.add(node3);          nodeList.add(node4);          nodeList.add(node5);          nodeList.add(node6);          nodeList.add(node7);          nodeList.add(node8);  }StringBuffer returnStr=new StringBuffer();      public void recursionFn(List list , Node node){          if(hasChild(list,node)){              returnStr.append("{id:");            returnStr.append(node.getId());            returnStr.append(",parentId:");            returnStr.append(node.getParentId());            returnStr.append(",children:[");              List childList = getChildList(list,node);              Iterator it = childList.iterator();              while(it.hasNext()){                  Node n = (Node)it.next();                  recursionFn(list,n);              }              returnStr.append("]},");          }else{              returnStr.append("{id:");            returnStr.append(node.getId());            returnStr.append(",parentId:");            returnStr.append(node.getParentId());            returnStr.append(",leaf:true},");          }                }      public boolean hasChild(List list, Node node){  //判断是否有子节点    return getChildList(list,node).size()>0?true:false;    }    public List getChildList(List list , Node node){  //得到子节点列表        List li = new ArrayList();          Iterator it = list.iterator();          while(it.hasNext()){              Node n = (Node)it.next();              if(n.getParentId()==node.getId()){                  li.add(n);              }          }          return li;      }    public String modifyStr(String returnStr){//修饰一下才能满足Extjs的Json格式    return ("["+returnStr+"]").replaceAll(",]", "]");        }    public static void main(String[] args) {          Recursion r = new Recursion();          r.recursionFn(r.nodeList, new Node(1,0));          System.out.println(r.modifyStr(r.returnStr.toString()));      }  }

import java.util.ArrayList;import java.util.Iterator;import java.util.List;public class Recursion {List nodeList =new ArrayList();Recursion(){//构造方法里初始化模拟ListNode node1 = new Node(1,0);          Node node2 = new Node(2,1);          Node node3 = new Node(3,1);          Node node4 = new Node(4,2);          Node node5 = new Node(5,2);          Node node6 = new Node(6,2);          Node node7 = new Node(7,6);          Node node8 = new Node(8,6);                    nodeList.add(node1);          nodeList.add(node2);          nodeList.add(node3);          nodeList.add(node4);          nodeList.add(node5);          nodeList.add(node6);          nodeList.add(node7);          nodeList.add(node8);  }StringBuffer returnStr=new StringBuffer();      public void recursionFn(List list , Node node){          if(hasChild(list,node)){              returnStr.append("{id:");            returnStr.append(node.getId());            returnStr.append(",parentId:");            returnStr.append(node.getParentId());            returnStr.append(",children:[");              List childList = getChildList(list,node);              Iterator it = childList.iterator();              while(it.hasNext()){                  Node n = (Node)it.next();                  recursionFn(list,n);              }              returnStr.append("]},");          }else{              returnStr.append("{id:");            returnStr.append(node.getId());            returnStr.append(",parentId:");            returnStr.append(node.getParentId());            returnStr.append(",leaf:true},");          }                }      public boolean hasChild(List list, Node node){  //判断是否有子节点    return getChildList(list,node).size()>0?true:false;    }    public List getChildList(List list , Node node){  //得到子节点列表        List li = new ArrayList();          Iterator it = list.iterator();          while(it.hasNext()){              Node n = (Node)it.next();              if(n.getParentId()==node.getId()){                  li.add(n);              }          }          return li;      }    public String modifyStr(String returnStr){//修饰一下才能满足Extjs的Json格式    return ("["+returnStr+"]").replaceAll(",]", "]");        }    public static void main(String[] args) {          Recursion r = new Recursion();          r.recursionFn(r.nodeList, new Node(1,0));          System.out.println(r.modifyStr(r.returnStr.toString()));      }  }

Main方法运行效果如下：
[{id:1,parentId:0,children:[{id:2,parentId:1,children:[{id:4,parentId:2,leaf:true},{id:5,parentId:2,leaf:true},{id:6,par
entId:2,children:[{id:7,parentId:6,leaf:true},{id:8,parentId:6,leaf:true}]}]},{id:3,parentId:1,leaf:true}]}]
在具体的应用中稍加修改即可 

（记得，return 要" return r.modifyStr(r.returnStr.toString());  "