Java-Mybatis-Spring

概念

• 什么是 MyBatis-Spring？

  • MyBatis-Spring会帮助你将MyBatis代码无缝地整合到Spring中。它将允许MyBatis参与到Spring的事务管理之中，创建映射器mapper和SqlSession并注入到bean中，以及将Mybatis的异常转换为Spring的DataAccessException。最终，可以做到应用代码不依赖于MyBatis，Spring或MyBatis-Spring。

核心原理

• 跟单独使用mybatis的区别

  • 跟单独使用Mybatis类似，只是在此基础上让将Mybatis在Spring的配置中注册为bean，然后让Spring接管了Mybatis的一些配置项（甚至可以让Spring全部接管Mybatis配置，并删除原来的mybatis-config.xml核心配置文件）。
  • 最终Mybatis在Spring中呈现为一个实现类为SqlSessionTemplate的bean（习惯上命名为：sqlSession），供程序在任意地方调用。
  • Spring接管Mybatis以后多了一个实现类，在该类中定义一个sqlSession属性，并增加setter，然后在Spring注册bean并注入sqlSession属性即可。
  • 新版本中还用另一种方式，让这个实现类继承SqlSessionDaoSupport，调用getSqlSession()方法你会得到一个SqlSessionTemplate。==注意：这种方式需要在bean中注入sqlSessionFactory属性，而不是sqlSession。==

• 其中两个核心bean

  • sqlSessionFactory（SqlSessionFactoryBean）
  • sqlSession（SqlSessionTemplate）

具体实现核心代码

• 目录机构

  • module

    • main

      • java

        • mapper

          • UserMapper.java
          • UserMapper.xml
          • UserMapperImpl.java
          • UserMapperImpl2.java

        • pojo

          • User.java

      • resources

        • applicationContext.xml
        • jdbc.properties
        • mybatis-config.xml
        • spring-dao.xml

    • test

      • java

        • UserMapperTest.java
  • pom.xml

• 配置文件（resources）

  • pom.xml

    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis-spring -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis-spring</artifactId>
        <version>2.0.6</version>
    </dependency>

  • jdbc.properties

    jdbc.driverClassName=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/jdbc_test?useSSL=false&characterEncoding=utf8&serverTimezone=Asia/Shanghai
    jdbc.username=root
    jdbc.password=root

  • 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>
        <settings>
            <setting name="logImpl" value="STDOUT_LOGGING"/>
        </settings>
        <typeAliases>
            <package name="cn.cnyasin.pojo"/>
        </typeAliases>
        <mappers>
            <mapper resource="cn/cnyasin/mapper/UserMapper.xml"/>
        </mappers>
    </configuration>

  • spring-dao.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:context="http://www.springframework.org/schema/context"
           xsi:schemaLocation="
           http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd
    ">
        <!-- 读取jdbc配置文件 -->
        <context:property-placeholder location="jdbc.properties"/>
        <!-- 定义DataSource：c3p0 dbcp druid -->
        <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
            <property name="driverClassName" value="${jdbc.driverClassName}"/>
            <property name="url" value="${jdbc.url}"/>
            <property name="username" value="${jdbc.username}"/>
            <property name="password" value="${jdbc.password}"/>
        </bean>
        <!-- 注册sqlSessionFactory -->
        <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dataSource"/>
            <!-- 绑定mybatis配置文件 -->
            <property name="configLocation" value="classpath:mybatis-config.xml"/>
            <!--<property name="mapperLocations" value="classpath:cn/cnyasin/mapper/UserMapper.xml"/>-->
        </bean>
        <!-- 注册sqlSession -->
        <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
            <!-- 注入SQLSessionFactory：只能通过构造器，因为他无set方法 -->
            <constructor-arg index="0" ref="sqlSessionFactory"/>
        </bean>
    </beans>

  • applicationContext.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="
           http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
    ">
        <!-- 导入其他配置文件 -->
        <import resource="spring-dao.xml"/>
        <!-- mapper -->
        <!-- 方式一 -->
        <bean id="userMapper" class="cn.cnyasin.mapper.UserMapperImpl">
            <property name="sqlSession" ref="sqlSession"/>
        </bean>
        <!-- 方式二 -->
        <bean id="userMapper2" class="cn.cnyasin.mapper.UserMapperImpl2">
            <property name="sqlSessionFactory" ref="sqlSessionFactory"/>
        </bean>
    </beans>

• java代码

  • UserMapper.java

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

  • 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="cn.cnyasin.mapper.UserMapper">
        <resultMap id="userList" type="user">
            <result property="createdAt" column="created_at"/>
        </resultMap>
        <select id="getAll" resultMap="userList">
            select * from user
        </select>
    </mapper>

  • UserMapperImpl.java

    public class UserMapperImpl implements UserMapper {
        private SqlSessionTemplate sqlSession;
        public void setSqlSession(SqlSessionTemplate sqlSession) {
            this.sqlSession = sqlSession;
        }
        public List<User> getAll() {
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
            return userMapper.getAll();
        }
    }

  • UserMapperImpl2.java

    public class UserMapperImpl2 extends SqlSessionDaoSupport implements UserMapper{
        public List<User> getAll() {
            return getSqlSession().getMapper(UserMapper.class).getAll();
        }
    }

  • User.java

    @NoArgsConstructor
    @AllArgsConstructor
    @Data
    public class User {
        private int id;
        private String username;
        private String email;
        private String password;
        private long balance;
        private long createdAt;
    }

  • UserMapperTest.java

    public class UserMapperTest {
        @Test
        public void getAllTest() {
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            UserMapper userMapper = context.getBean("userMapper", UserMapper.class);
            System.out.println(userMapper.getAll());
        }
        @Test
        public void getAllTest2() {
            ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
            UserMapper userMapper = context.getBean("userMapper2", UserMapper.class);
            System.out.println(userMapper.getAll());
        }
    }

Mybatis配合Spring开启事务

• 如何理解？

  • 不要被这个标题误导哦，Mybatis的事务非常笨重，而MybatisSpring中Mybatis默认关闭了事务，你可以直接使用Spring的事务。

    • XML方式（配置事务通知、事务切入点）
    • AOP方式（Spring开启注解、使用注解开启事务）

• 注意：最终实例化bean的时候，约束类必须是接口而不是接口的实现类，否则报错：org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'userMapper' is expected to be of type......

  • 错误用法：UserMapperImpl userMapper = context.getBean("userMapper", UserMapperImpl.class);
  • 正确用法：UserMapper userMapper = context.getBean("userMapper", UserMapper.class);

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