在mapper文件中添加 keyProperty=“id” useGeneratedKeys=“true”

      <insert id="insertUser"  keyProperty="id" useGeneratedKeys="true">
		INSERT INTO serv_user(
				id,
				name,
				password,
				open_id
		) VALUES (
				#{id},
				#{name},
				#{password},
				#{openId}
	)

当插入完成时,会自动的把id的值带回到传入的对象中

    public  void insertUser(User user){
    	 Integer id=   userMapper.insertUser(user);
    	  
    	 System.out.println("userId==>"+user.getId());
    }