前提概要

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

下面是实例介绍。

---

1.环境配置

工程目录结构如下

SqlMapConfig.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>

    <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/db_pwc" />

                <property name="username" value="pwc" />

                <property name="password" value="123456" />

            </dataSource>

        </environment>

    </environments>

    <mappers>

        <mapper resource="com/pwc/dao/mapper/UserMapper.xml" />

    </mappers>

</configuration>

---

2.Mapper映射接口（UserMapper.java)和Mapper映射表(UserMapper.xml)

UserMapper.java

package com.pwc.dao.mapper;

import java.util.List;

import com.pwc.pojo.User;

public interface UserMapper {

    public User findById(int id);

    public void deleteById(int id);

    public void insert(User user);

    public List<User> findByAge(int age);

}

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.pwc.dao.mapper.UserMapper">

    <select id="findById" parameterType="int" resultType="com.pwc.pojo.User">

        SELECT * FROM User WHERE id = #{id}

    </select>

    <insert id="insert" parameterType="com.pwc.pojo.User">

        INSERT INTO User(name,age) VALUES(#{name},#{age})

    </insert>

    <delete id="deleteById" parameterType="int">

        DELETE * FROM User WHERE id=#{id}

    </delete>

    <select id="findByAge" parameterType="int" resultType="com.pwc.pojo.User">

        SELECT * FROM User WHERE age=#{age}

    </select>

</mapper>

---

3.测试

测试类

package com.pwc.test;

import org.apache.ibatis.session.SqlSession;

import org.apache.ibatis.session.SqlSessionFactory;

import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.pwc.dao.mapper.UserMapper;

import com.pwc.pojo.User;

public class Test {

    public static void main(String[] args) {

        SqlSessionFactoryBuilder builder=new SqlSessionFactoryBuilder();

        SqlSessionFactory factory=builder.build(Test.class.getClassLoader().getResourceAsStream("SqlMapConfig.xml"));

        SqlSession session = factory.openSession();

        UserMapper mapper = session.getMapper(UserMapper.class);

        User user = mapper.findById(1);

        session.close();

        System.out.println(user);

    }

}

测试结果如下
User [id=1, name=pwc, age=18]

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