mabatis之mapper代理开发

1.1     Mapper动态代理方式   

1.1.1  开发规范

        Mapper接口开发方法只需要程序员编写Mapper接口（相当于Dao接口），由Mybatis框架根据接口定义创建接口的动态代理对象，代理对象的方法体同上边Dao接口实现类方法。

Mapper接口开发需要遵循以下规范：

1、  Mapper.xml文件中的namespace与mapper接口的类路径相同。

2、  Mapper接口方法名和Mapper.xml中定义的每个statement的id相同

3、  Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql 的parameterType的类型相同

4、  Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同 

1.1.2 Mapper.xml(映射文件)

        定义mapper映射文件UserMapper.xml（内容同Users.xml），需要修改namespace的值为 UserMapper接口路径。将UserMapper.xml放在classpath 下mapper目录 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="cn.itcast.mybatis.mapper.UserMapper">
<!-- 根据id获取用户信息 -->
    <select id="findUserById" parameterType="int" resultType="cn.itcast.mybatis.po.User">
        select * from user where id = #{id}
    </select>
<!-- 自定义条件查询用户列表 -->
    <select id="findUserByUsername" parameterType="java.lang.String" 
            resultType="cn.itcast.mybatis.po.User">
       select * from user where username like '%${value}%' 
    </select>
<!-- 添加用户 -->
    <insert id="insertUser" parameterType="cn.itcast.mybatis.po.User">
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
        select LAST_INSERT_ID() 
    </selectKey>
      insert into user(username,birthday,sex,address) 
      values(#{username},#{birthday},#{sex},#{address})
    </insert>

</mapper>

1.1.3 Mapper.java(接口文件)

package com.mybatis.mapper;

import java.util.List;

import com.mybatis.po.User;

public interface UserMapper {
    //根据用户id查询用户信息
    public User findUserById(int id) throws Exception;
    //查询用户列表
    public List<User> findUserByUsername(String username) throws Exception;
    //添加用户信息
    public void insertUser(User user)throws Exception; 

}

接口定义有如下特点：

1、  Mapper接口方法名和Mapper.xml中定义的statement的id相同

2、  Mapper接口方法的输入参数类型和mapper.xml中定义的statement的parameterType的类型相同

3、  Mapper接口方法的输出参数类型和mapper.xml中定义的statement的resultType的类型相同

1.1.4  加载UserMapper.xml文件

<?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.mybatis.mapper.UserMapper">
<!-- 根据id获取用户信息 -->
    <select id="findUserById" parameterType="int" resultType="com.mybatis.po.User">
        select * from user where id = #{id}
    </select>
<!-- 自定义条件查询用户列表 -->
    <select id="findUserByUsername" parameterType="java.lang.String" 
            resultType="com.mybatis.po.User">
       select * from user where username like '%${value}%' 
    </select>
<!-- 添加用户 -->
    <insert id="insertUser" parameterType="com.mybatis.po.User">
    <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
        select LAST_INSERT_ID() 
    </selectKey>
      insert into user(username,birthday,sex,address) 
      values(#{username},#{birthday},#{sex},#{address})
    </insert>

</mapper>

1.1.5 测试

package test;

import static org.junit.Assert.*;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Date;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import com.mybatis.mapper.UserMapper;
import com.mybatis.po.User;

public class UserMapperTest {
    
    private SqlSessionFactory sqlSessionFactory;
    
    @Before
    public void init() throws IOException{
        SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
        InputStream inputStream = Resources.getResourceAsStream("SqlMapConfig.xml");
        sqlSessionFactory = builder.build(inputStream);
    }

    @Test
    public void testFindUserById() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.findUserById(10);
        System.out.println(user);
    }

    @Test
    public void testFindUserByUsername() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> list = mapper.findUserByUsername("张");
        for (User user : list) {
            System.out.println(user);
        }
    }

    @Test
    public void testInsertUser() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user=new User();
        user.setUsername("张益达");
        user.setAddress("上海");
        user.setBirthday(new Date());
        user.setSex("2");
        mapper.insertUser(user);
        System.out.println(user.getId());
    }

}

1.1.6 小结

  selectOne和selectList

动态代理对象调用sqlSession.selectOne()和sqlSession.selectList()是根据mapper接口方法的返回值决定，如果返回list则调用selectList方法，如果返回单个对象则调用selectOne方法。

 

 namespace

mybatis官方推荐使用mapper代理方法开发mapper接口，程序员不用编写mapper接口实现类，使用mapper代理方法时，输入参数可以使用pojo包装对象或map对象，保证dao的通用性。