解析java樹形結構

思路一：

一、準備表結構及對應的表數據
a、表結構：

create table TB_TREE ( CID NUMBER not null, CNAME VARCHAR2(50), PID NUMBER //父節點 )

b、表數據：

insert into tb_tree (CID, CNAME, PID) values (1, '中國', 0); insert into tb_tree (CID, CNAME, PID) values (2, '北京市', 1); insert into tb_tree (CID, CNAME, PID) values (3, '廣東省', 1); insert into tb_tree (CID, CNAME, PID) values (4, '上海市', 1); insert into tb_tree (CID, CNAME, PID) values (5, '廣州市', 3); insert into tb_tree (CID, CNAME, PID) values (6, '深圳市', 3); insert into tb_tree (CID, CNAME, PID) values (7, '海珠區', 5); insert into tb_tree (CID, CNAME, PID) values (8, '天河區', 5); insert into tb_tree (CID, CNAME, PID) values (9, '福田區', 6); insert into tb_tree (CID, CNAME, PID) values (10, '南山區', 6); insert into tb_tree (CID, CNAME, PID) values (11, '密雲縣', 2); insert into tb_tree (CID, CNAME, PID) values (12, '浦東', 4);

二、TreeNode對象，對應tb_tree

public class TreeNode implements Serializable { private Integer cid; private String cname; private Integer pid; private List nodes = new ArrayList();   public TreeNode() { }   //getter、setter省略 }

三、測試數據

public class TreeNodeTest { @Test public void loadTree() throws Exception{ System.out.println(JsonUtils.javaToJson(recursiveTree(1))); }   /** * 遞歸算法解析成樹形結構 * * @param cid * @return * @author jiqinlin */ public TreeNode recursiveTree(int cid) { //根據cid獲取節點對象(SELECT * FROM tb_tree t WHERE t.cid=?) TreeNode node = personService.getreeNode(cid); //查詢cid下的全部子節點(SELECT * FROM tb_tree t WHERE t.pid=?) List childTreeNodes = personService.queryTreeNode(cid); //遍歷子節點 for(TreeNode child : childTreeNodes){ TreeNode n = recursiveTree(child.getCid()); //遞歸 node.getNodes().add(n); }   return node; } }

輸出的json格式以下：

{
    "cid": 1,     "nodes": [         {             "cid": 2,             "nodes": [                 {                     "cid": 11,                     "nodes": [                                               ],                     "cname": "密雲縣",                     "pid": 2                 }             ],             "cname": "北京市",             "pid": 1         },         {             "cid": 3,             "nodes": [                 {                     "cid": 5,                     "nodes": [                         {                             "cid": 7,                             "nodes": [                                                               ],                             "cname": "海珠區",                             "pid": 5                         },                         {                             "cid": 8,                             "nodes": [                                                               ],                             "cname": "天河區",                             "pid": 5                         }                     ],                     "cname": "廣州市",                     "pid": 3                 },                 {                     "cid": 6,                     "nodes": [                         {                             "cid": 9,                             "nodes": [                                                               ],                             "cname": "福田區",                             "pid": 6                         },                         {                             "cid": 10,                             "nodes": [                                                               ],                             "cname": "南山區",                             "pid": 6                         }                     ],                     "cname": "深圳市",                     "pid": 3                 }             ],             "cname": "廣東省",             "pid": 1         },         {             "cid": 4,             "nodes": [                 {                     "cid": 12,                     "nodes": [                                               ],                     "cname": "浦東",                     "pid": 4                 }             ],             "cname": "上海市",             "pid": 1         }     ],     "cname": "中國",     "pid": 0 }

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思路二：

數據庫  id,name,parent_id

java對象：

private class TreeNode{
    private String id;
    private String name;
    private String parentId;
    private List<TreeNode> children;
    
    // TODO getter/setter
}

樹構造代碼以下：

        List<TreeNode> menuList = xxManager.findAllMenu();
        
        List<TreeNode> nodeList = new ArrayList<TreeNode>();
        for(TreeNode node1 : menuList){
            boolean mark = false;
            for(TreeNode node2 : menuList){
                if(node1.getParentId()!=null && node1.getParentId().equals(node2.getId())){
                    mark = true;
                    if(node2.getChildren() == null)
                        node2.setChildren(new ArrayList<TreeNode>());
                    node2.getChildren().add(node1); 
                    break;
                }
            }
            if(!mark){
                nodeList.add(node1); 
            }
        }
        //轉爲json格式        
        String json = JSONArray.fromObject(nodeList).toString();
        System.out.println("json:"+json);

原理以下圖了：