MyBatis笔记——Mapper动态代理

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。

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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>

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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>

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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]