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MyBatis及 SpringBoot解决代码冗余

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SpringBoot整合JDBCTemplate以及事务管理

– 贴一篇博客https://blog.csdn.net/wx5040257/article/details/79465307

MyBatis

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<!--mybatis-->
	<dependency>
		<groupId>org.mybatis</groupId>
		<artifactId>mybatis</artifactId>
	</dependency>

⭐⭐ 配置注意一个问题：mybatis-config和applicaton.properties中都要配置mysql数据库的连接信息

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##数据库连接信息(基于JDBC)
spring.datasource.url = jdbc:mysql://127.0.0.1:3306/parking_lot_swpu?serverTimezone=UTC
spring.datasource.username = root
spring.datasource.password = Qwer;t592665
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
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<dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/parking_lot_swpu?serverTimezone=UTC"/>
                <property name="username" value="root"/>
                <property name="password" value="Qwer;t592665"/>
            </dataSource>

引入Mapper – 为了解决代码冗余问题

例如：

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public class UserDao {
    private SqlSessionFactory sqlSessionFactory = SqlSessionFactoryUtils.getInstance();

    public User getUserById(Integer id) {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        User user = (User) sqlSession.selectOne("org.javaboy.mybatis.mapper.UserDao.getUserById", id);
        sqlSession.close();
        return user;
    }

    public Integer addUser(User user) {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        int insert = sqlSession.insert("org.javaboy.mybatis.mapper.UserDao.addUser", user);
        sqlSession.commit();
        sqlSession.close();
        return insert;
    }

    public Integer addUser2(User user) {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        int insert = sqlSession.insert("org.javaboy.mybatis.mapper.UserDao.addUser2", user);
        sqlSession.commit();
        sqlSession.close();
        return insert;
    }

    public Integer deleteUserById(Integer id) {
        SqlSession ssqlSession = sqlSessionFactory.openSession();
        int desete = sqlSession.delete("com.swpu.htht.mapper.UserDao.deleteUserById",id);
        sqlSession.commit();
        sqlSession.close();
        return delete;
    }

    public Integer updateUser(User user) {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        int delete = sqlSession.delete("org.javaboy.mybatis.mapper.UserDao.updateUser", user);
        sqlSession.commit();
        sqlSession.close();
        return delete;
    }

    public List<User> getAllUser() {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        List<User> users = sqlSession.selectList("org.javaboy.mybatis.mapper.UserDao.getAllUser");
        sqlSession.close();
        return users;
    }
}

然后，和这个UserDao对应的，还有一个UserDaoMapper.xml：

当然，观察上面的UserDao.class，你可以发现大部分代码冗余，其实这些都可以模块化。

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<?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="org.javaboy.mybatis.mapper.UserDao">

    <select id="getUserById" resultType="org.javaboy.mybatis.model.User">
        select * from user where id=#{id};
    </select>
    
    <insert id="addUser" parameterType="org.javaboy.mybatis.model.User">
        insert into user (username,address) values (#{username},#{address});
    </insert>
    
    <insert id="addUser2" parameterType="org.javaboy.mybatis.model.User">
        <selectKey resultType="java.lang.String" keyProperty="id" order="BEFORE">
            select uuid();
        </selectKey>
        insert into user (id,username,address) values (#{id},#{username},#{address});
    </insert>

    <delete id="deleteUserById" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>

    <update id="updateUser" parameterType="org.javaboy.mybatis.model.User">
        update user set username = #{username} where id=#{id};
    </update>

    <select id="getAllUser" resultType="org.javaboy.mybatis.model.User">
        select * from user;
    </select>
</mapper>

我们说过UserDao.class的问题，现在我们将之模块化：原理很简单，就是Spring所说的动态代理。我们可以将当前方法简化成一个接口。

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package org.javaboy.mapper;

public interface UserMapper {
    User getUserById(Integer id);

    Integer addUser(User user);

    Integer addUser2(User user);

    Integer deleteUserById(Integer id);

    Integer updateUser(User user);

    List<User> getAllUser();
}

这个接口对应的Mapper文件如下（注意，UserMapper.xml 和 UserMapper 需要放在同一个包下面，但是分别在project的java和Resource中）

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<?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="org.javaboy.mybatis.mapper.UserMapper">

    <select id="getUserById" resultType="org.javaboy.mybatis.model.User">
        select * from user where id=#{id};
    </select>
    <insert id="addUser" parameterType="org.javaboy.mybatis.model.User">
        insert into user (username,address) values (#{username},#{address});
    </insert>
    <insert id="addUser2" parameterType="org.javaboy.mybatis.model.User">
        <selectKey resultType="java.lang.String" keyProperty="id" order="BEFORE">
            select uuid();
        </selectKey>
        insert into user (id,username,address) values (#{id},#{username},#{address});
    </insert>

    <delete id="deleteUserById" parameterType="java.lang.Integer">
        delete from user where id=#{id}
    </delete>

    <update id="updateUser" parameterType="org.javaboy.mybatis.model.User">
        update user set username = #{username} where id=#{id};
    </update>

    <select id="getAllUser" resultType="org.javaboy.mybatis.model.User">
        select * from user;
    </select>
</mapper>

使用上述方式，就可以代替UserDao了。

然后我们需要在MyBatis全局配置中配置UserMapper：

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<mappers>
    <package name="org.javaboy.mybatis.mapper"/>
</mappers>

最后就可以加载配置文件，获取UserMapper，并调用方法：

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public class Main {
    /**
    *提供入口
    */
    public static void main(String[] args) {
        SqlSessionFactory instance = SqlSessionFactoryUtils.getInstance();
        SqlSession sqlSession = instance.openSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> allUser = mapper.getAllUser();
        System.out.println(allUser);
    }
}

resultMap – 自定义映射的结果集

先看一个基本用法：

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<resultMap id="MyResultMap" type="org.javaboy.mybatis.model.User">
    <id column="id" property="id"/>
    <result column="username" property="username"/>
    <result column="address" property="address"/>
</resultMap>

在上面的ResultMap中，id用来描述主键，column是数据库查的列名，property则是对象中的属性名。

然后在查询结果中，定义返回值使用这个ResultMap：

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<select id="getUserById" resultMap="MyResultMap">
    select * from user
    
    where id=#{id};
</select>

也可以在resultMap中指定要调用的构造方法，指定方式如下：

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<resultMap id="MyResultMap" type="org.javaboy.mybatis.model.User">
    <constructor>
        <idArg column="id" name="id"/>
        <arg column="username" name="username"/>
    </constructor>
</resultMap>

上面的resultMap表示使用两个参数的构造方法去构造一个实例。⭐注意：name属性表示构造方法中的变量名，默认情况下，变量名是arg0, arg1，或者parm0, parm1， 如果需要自定义，我们可以在构造方法中，手动加上@Param注解。 

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public User(@Param("id") Integer id, @Param("username") String username) {
        this.id = id;
        this.username = username;
    }