Mybatis框架三：DAO层开发、Mapper动态代理开发

这里是最基本的搭建：http://www.cnblogs.com/xuyiqing/p/8600888.html

接下来做到了简单的增删改查：http://www.cnblogs.com/xuyiqing/p/8601506.html

但是发现代码重复过多等问题

接下来整合并实现DAO开发：

一：原始DAO开发：

package dao;

import pojo.User;

public interface UserDao {
    public User selectUserById(Integer id);
}

package dao;

import java.util.List;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;

import pojo.User;

public class UserDaoImpl implements UserDao {

    //注入
    private SqlSessionFactory sqlSessionFactory;
    public UserDaoImpl(SqlSessionFactory sqlSessionFactory) {
        this.sqlSessionFactory = sqlSessionFactory;
    }

    //通过用户ID查询一个用户
    public User selectUserById(Integer id){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession.selectOne("test.findUserById", id);
    }
    //通过用户名称模糊查询
    public List<User> selectUserByUsername(Integer id){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession.selectList("test.findUserById", id);
    }
}

测试类：

package junit;

import java.io.InputStream;

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

import dao.UserDao;
import dao.UserDaoImpl;
import pojo.User;

public class DaoTest {
    public SqlSessionFactory sqlSessionFactory;
    @Before
    public void before() throws Exception {
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
    }
    @Test
    public void testDao() throws Exception {
        UserDao userDao = new UserDaoImpl(sqlSessionFactory);
        User user = userDao.selectUserById(10);
        System.out.println(user);
    }
}

但是还是发现代码重复、浪费资源等问题：

于是想到Mapper动态代理开发：

package mapper;

import pojo.User;

public interface UserMapper {

    //遵循四个原则
    //接口 方法名  == User.xml 中 id 名
    //返回值类型  与  Mapper.xml文件中返回值类型要一致
    //方法的入参类型 与Mapper.xml中入参的类型要一致
    //命名空间 绑定此接口

    //这里如果返回的是一个对象，则调用selectOne方法
    //如果是List，则调用selectlist方法
    public User findUserById(Integer id);

}

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">
<!-- 写Sql语句   -->
<mapper namespace="mapper.UserMapper">
    <!-- 通过ID查询一个用户 -->
    <select id="findUserById" parameterType="Integer" resultType="pojo.User">
        select * from user where id = #{v}
    </select>

    <!-- //根据用户名称模糊查询用户列表
    #{}    select * from user where id = ？    占位符  ? ==  ‘五‘
    ${}    select * from user where username like ‘%五%‘  字符串拼接  

     -->
    <select id="findUserByUsername" parameterType="String" resultType="pojo.User">
        select * from user where username like "%"#{haha}"%"
    </select>

    <!-- 添加用户 -->
    <insert id="insertUser" parameterType="pojo.User">
        <selectKey keyProperty="id" resultType="Integer" order="AFTER">
            select LAST_INSERT_ID()
        </selectKey>
        insert into user (username,birthday,address,sex)
        values (#{username},#{birthday},#{address},#{sex})
    </insert>

    <!-- 更新 -->
    <update id="updateUserById" parameterType="pojo.User">
        update user
        set username = #{username},sex = #{sex},birthday = #{birthday},address = #{address}
        where id = #{id}
    </update>

    <!-- 删除 -->
    <delete id="deleteUserById" parameterType="Integer">
        delete from user
        where id = #{vvvvv}
    </delete>

</mapper>

主配置文件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/mybatis?characterEncoding=utf-8" />
                <property name="username" value="root" />
                <property name="password" value="xuyiqing" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

测试类：

package junit;
import java.io.InputStream;

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.Test;

import mapper.UserMapper;
import pojo.User;

public class MybatisMapperTest {

    @Test
    public void testMapper() throws Exception {
        String resource = "sqlMapConfig.xml";
        InputStream in = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sqlSessionFactory.openSession();

        //SqlSession自动为接口生成一个实现类
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        User user = userMapper.findUserById(10);
        System.out.println(user);
    }
}

通常情况下，建议使用Mapper动态代理开发

原文地址：https://www.cnblogs.com/xuyiqing/p/8605786.html