id,pid,数据库递归调用展示树形菜单的示例

public class TreeDAO{
        public String readTree(int id,int level){
		String str = "";
		
		Connection conn = null;
		PreparedStatement pstmt = null;
		ResultSet rs = null;
				
		String sql = "SELECT * FROM earth WHERE pid=?";
		
		try{
			conn = DBConnect.getConn();
			pstmt = conn.prepareStatement(sql);
			pstmt.setInt(1, id);
			
			rs = pstmt.executeQuery();
			while(rs.next()){
				for (int i = 0; i < level; i++) {
					str += "-->>";
				}
				str += rs.getInt("id")+"="+rs.getString("name")+"\n";
				
				str += readTree(rs.getInt("id"),++level);
				
				--level;
			}
			
		}catch(Exception e){
			e.printStackTrace();
			
		}finally{			
			DBConnect.closeRs(rs);
			DBConnect.closePstmt(pstmt);
			DBConnect.closeConn(conn);
		}
		
		return str;
	
	}


	public static void main(String[] args) {
		TreeDao treeDao = new TreeDao();
		String str = treeDao.readTree(0, 1);
		System.out.println(str);
	}
}

 

CREATE TABLE `earth` (
  `id` int(11) NOT NULL,
  `pid` int(11) NOT NULL,
  `name` varchar(50) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

#
# Dumping data for table earth
#

INSERT INTO `earth` VALUES (1,0,'亚洲');
INSERT INTO `earth` VALUES (2,0,'欧洲');
INSERT INTO `earth` VALUES (3,0,'美洲');
INSERT INTO `earth` VALUES (4,0,'非洲');
INSERT INTO `earth` VALUES (5,1,'中国');
INSERT INTO `earth` VALUES (6,1,'小日本');
INSERT INTO `earth` VALUES (7,1,'棒子');
INSERT INTO `earth` VALUES (8,3,'美国');
INSERT INTO `earth` VALUES (9,5,'北京');
INSERT INTO `earth` VALUES (10,5,'上海');
INSERT INTO `earth` VALUES (11,5,'西安');
INSERT INTO `earth` VALUES (12,9,'北京大学');
INSERT INTO `earth` VALUES (13,11,'西安交大');

 

 

 

out:

-->>1=亚洲
-->>-->>5=中国
-->>-->>-->>9=北京
-->>-->>-->>-->>12=北京大学
-->>-->>-->>10=上海
-->>-->>-->>11=西安
-->>-->>-->>-->>13=西安交大
-->>-->>6=小日本
-->>-->>7=棒子
-->>2=欧洲
-->>3=美洲
-->>-->>8=美国
-->>4=非洲