🍁Mapper代理

传统 dao层开发有一些地方是重复工作的，而 MyBatis 提供了另一种高效开发的方式，那就是Mapper代理，但是使用Mapper代理开发应该遵循Mybatis 的规范。

第一步搭建MyBatis项目：MyBatis入门程序

🍁用mapper代理的方式开发dao层要遵循一些规范:

1、Mapper接口和映射文件在同一个目录下，映射文件一般放在resources中。
2、userMapper.xml中namespace指定为mapper接口的全限定名。

<mapper namespace="com.jkj.Mapper.UserMapper">

3、userMapper.xml中id就是UserMapper.java中方法名

<select id="selectAll" resultType="com.jkj.pojo.User">

4、配置别名

• 在配置文件(mybatis-config.xml或者是其他名字)中的正确位置加入以下代码：

 <!--起别名，不区分大小写-->
    <typeAliases>
        <package name="com.jkj.pojo"/>
    </typeAliases>

• 设置别名后之前的select就可以改成：

<select id="selectAll" resultType="User">
    select * from tb_user;
  </select>

🍁编码

🔥调用SQLSession的getMapper方法获取Mapper接口的代理对象

UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

🔥调用对应的方法执行sql语句

List<User> users = userMapper.selectAll();

🍁案例

user.java:

package com.jkj.pojo;

public class User {
    private Integer id;
    private String username;
    private String password;
    private String gender;
    private String addr;

    public User() {
    }

    public User(Integer id, String username, String password, String gender, String addr) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.gender = gender;
        this.addr = addr;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public String getAddr() {
        return addr;
    }

    public void setAddr(String addr) {
        this.addr = addr;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", gender='" + gender + '\'' +
                ", addr='" + addr + '\'' +
                '}';
    }
}

UserMapper.java:

package com.jkj.Mapper;

import com.jkj.pojo.User;

import java.util.List;

public interface UserMapper {
    List<User> selectAll();
}

userMapper.xml:

<?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.jkj.Mapper.UserMapper">
    <select id="selectAll" resultType="User">
    select * from tb_user;
  </select>
</mapper>

mybatis-config.xml:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<!--configuration core file-->
<configuration>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>
     <!--加载sql映射文件-->
    <mappers>
        <!--<mapper resource="com/jkj/Mapper/userMapper.xml"/>-->
        <!--Mapper代理方式-->
        <package name="com.jkj.Mapper"/>
    </mappers>
</configuration>

MybatisDemo.java测试类：

import com.jkj.Mapper.UserMapper;
import com.jkj.pojo.User;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MybatisDemo {
    public static void main(String[] args) throws IOException {
        //1.加载MyBatis的核心配置文件获取sqlSessionFactory
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        //2.获取sqlSession,执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //获取UserMapper接口的代理对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.selectAll();
        System.out.println(users);
        //4.释放资源
        sqlSession.close();
    }
}

运行结果：

[User{id=1, username='小马哥', password='111', gender='男', addr='北京'}, User{id=2, username='小飞侠', password='222', gender='男', addr='上海'}, User{id=3, username='马奎斯', password='333', gender='女', addr='西班牙'}]