Mybatis基础服务层数据层接口和对应Mapper.xml的关系

1.测试类，类中调用服务层UserServiceImpl

package com.lic.ibatis.test;

import com.lic.ibatis.entity.User;

import com.lic.ibatis.service.UserServiceImpl;

public class MybatisTest {

public static void main(String[] args) {

UserServiceImpl userService = new UserServiceImpl();

User user = userService.query(1);

System.out.println(user.toString());

}

}

2.服务层Service接口及实现类，类中调用UserMapper.java接口

//service接口

package com.lic.ibatis.service;

import com.lic.ibatis.entity.User;

public interface UserService {

User query(int id);

}

//service实现类

package com.lic.ibatis.service;

import com.lic.ibatis.dao.UserMapper;

import com.lic.ibatis.dao.UserMapperImpl;

import com.lic.ibatis.entity.User;

public class UserServiceImpl implements UserService{

UserMapper userMapper=new UserMapperImpl();

@Override

public User query(int id) {

return userMapper.getUserById(id);

}

}

3.mapper接口类 UserMapper.java　　

mybatis根据UserMapper.xml中配置的信息创建一个实现了UserMaper.java接口的代理类

package com.lic.ibatis.dao;

import com.lic.ibatis.entity.User;

public interface UserMapper {

//根据用户ID获取用户信息

User getUserById(int id);

}

5.UserMapper.xml信息如下:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.lic.ibatis.dao.UserMapper">

<select id="getUserById" parameterType="int" resultType="com.lic.ibatis.entity.User">

select * from user where id = #{id}

</select>

</mapper>

在UserMapper.xml中namespace等于UserMapper.java接口地址(即UserMapper的全限定名)；

UserMapper.java接口中的方法名和UserMapper.xml中的statement(<select>,<update>...标签)的id属性值一致;

UserMapper.java接口中的方法输入值参数和UserMapper.xml中statement的parameterType指定的类型一致。

UserMapper.java接口中的方法的返回值类型和UserMapper.xml中statement的resultType指定的类型一致。

4.mapper实现类UserMapperImpl.java　

package com.lic.ibatis.dao;

import com.lic.ibatis.entity.User;

import java.sql.*;

import java.util.Date;

public class UserMapperImpl implements UserMapper {

@Override

public User getUserById(int id) {

Connection connection=null;

PreparedStatement preparedStatement=null;

ResultSet resultSet=null;

try {

//注册驱动

Class.forName("com.mysql.jdbc.Driver");

//获取数据连接

connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/mybatis" , "root" , "m123" ) ;

//sql语句

String sql= "select * from user where id = ?";

//加载预执行对象

preparedStatement = connection.prepareStatement(sql);

//添加参数

preparedStatement.setInt(1,id);

//执行查询, 获取结果集

resultSet = preparedStatement.executeQuery();

User user=null;

//解析结果集,封装结果

while(resultSet.next()){

int userId = resultSet.getInt("id");

String username = resultSet.getString("username") ;

Date birthday = resultSet.getDate("birthday");

String sex = resultSet.getString("sex");

String address = resultSet.getString("address");

user = new User(String.valueOf(userId), username, String.valueOf(birthday), sex, address);

}

return user;

} catch (Exception e) {

e.printStackTrace();

}finally

//关闭相关资源

try {

if (resultSet !=null){

resultSet.close();

}

if (preparedStatement !=null){

preparedStatement.close();

}

if (connection !=null){

connection.close();

}

} catch (SQLException e) {

e.printStackTrace();

}

}

return null;

}

}