java面试之声明式事务声明式事务的原理

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mob64ca14038b36 2024-02-25 22:46:47

文章标签 java面试之声明式事务 spring5 声明式事务 java spring 文章分类 Java 后端开发

一、概述

事务：事务在项目开发过程非常重要，涉及到数据的一致性的问题，不容马虎！事务管理是企业级应用程序开发中必备技术，用来确保数据的完整性和一致性。事务就是把一系列的动作当成一个独立的工作单元，这些动作要么全部完成，要么全部不起作用

事务四个属性ACID

1. 原子性（atomicity）

事务是原子性操作，由一系列动作组成，事务的原子性确保动作要么全部完成，要么完全不起作用

2. 一致性（consistency）

一旦所有事务动作完成，事务就要被提交。数据和资源处于一种满足业务规则的一致性状态中

3. 隔离性（isolation）

可能多个事务会同时处理相同的数据，因此每个事务都应该与其他事务隔离开来，防止数据损坏

4. 持久性（durability）

事务一旦完成，无论系统发生什么错误，结果都不会受到影响。通常情况下，事务的结果被写到持久化存储器中

二、事务实现详情

1、创建基础项目，导入依赖

<dependencies>
    <!--mybatis相关-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.21</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.5</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.13</version>
    </dependency>
    <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.12</version>
    </dependency>

    <!--mybatis-spring整合-->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis-spring</artifactId>
        <version>2.0.5</version>
    </dependency>

    <!--spring相关-->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.2.8.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-jdbc</artifactId>
        <version>5.2.8.RELEASE</version>
    </dependency>
    <!--AOP织入-->
    <dependency>
        <groupId>org.aspectj</groupId>
        <artifactId>aspectjweaver</artifactId>
        <version>1.9.6</version>
    </dependency>
</dependencies>

<!--在build中配置resources，来防止我们资源导出失败的问题-->
<build>
    <resources>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>true</filtering>
        </resource>
    </resources>
</build>

2、实体类

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
  private int id;
  private String name;
  private String pwd;
}

3、接口、接口对应的Mapper映射

public interface UserMapper {
  List<User> selectUser();
  int addUser(User user);
  int delete(int id);
}

<?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.jason.dao.UserMapper">
    <select id="selectUser" resultType="User">
    select * from mybatis.user
  </select>

    <insert id="addUser" parameterType="com.jason.pojo.User">
        insert into user (id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>

    <!--人为制造错误-->
    <delete id="delete" parameterType="com.jason.pojo.User">
        deletes from user where id=#{id}
    </delete>
</mapper>

4、增加接口实现类（spring框架下，懂得...）

public class UserMapperImpl extends SqlSessionDaoSupport implements UserMapper {
  @Override
  public List<User> selectUser() {
    User user = new User(5,"晓东","222");
    UserMapper mapper = getSqlSession().getMapper(UserMapper.class);
    mapper.addUser(user);
    mapper.delete(5);
    return mapper.selectUser();
  }

  @Override
  public int addUser(User user) {
    UserMapper mapper = getSqlSession().getMapper(UserMapper.class);
    return mapper.addUser(user);
  }

  @Override
  public int delete(int id) {
    UserMapper mapper = getSqlSession().getMapper(UserMapper.class);
    return mapper.delete(id);
  }
}

5、配置mybatis文件（由于被spring整合，其存在意义不大，目的在于能够让别人知道这里还有mybatis，目录结构清晰一些）

<?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>

    <!--起别名-->
    <typeAliases>
        <typeAlias type="com.jason.pojo.User" alias="User"/>
    </typeAliases>
</configuration>

6、spring核心配置文件：（这里包含了数据源、sqlSessionFactory、SqlSessionTemplate、声明式事务、AOP实现事务的织入、事务的切入）这个文件是重点的重点

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop
       https://www.springframework.org/schema/aop/spring-aop.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd">


    <!--DataSource:使用Spring的数据源替换mybatis的配置c3p0/dbcp/druid-->
    <bean id="dataSource"
          class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
        <property name="url"
                  value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&useUnicode=true\
  &serverTimezone=UTC&characterEncoding=UTF-8"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
    </bean>


    <!--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:com/jason/dao/*.xml"/>
    </bean>


    <!--SqlSessionTemplate:就是我们使用的sqlSession-->
    <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
        <constructor-arg index="0" ref="sqlSessionFactory"/>
    </bean>


    <!--配置声明式事务-->
    <bean id="transactionManager"
          class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <constructor-arg ref="dataSource"/>
    </bean>


    <!--结合AOP实现事务的织入-->
    <!--配置事务通知-->
    <tx:advice id="txAdvice"
               transaction-manager="transactionManager">
        <!--给哪些方法配置事务-->
        <!--配置事务的传播特性：new propagation = -->
        <tx:attributes>
            <tx:method name="add" propagation="REQUIRED"/>
            <tx:method name="delete" propagation="REQUIRED"/>
            <tx:method name="update" propagation="REQUIRED"/>
            <tx:method name="query" read-only="true"/>
            <tx:method name="*" propagation="REQUIRED"/>
        </tx:attributes>
    </tx:advice>
    
    <!--配置事务的切入-->
    <aop:config>
        <aop:pointcut id="txtPointCut"
                      expression="execution(* com.jason.dao.*.*(..))"/>
        <aop:advisor advice-ref="txAdvice" pointcut-ref="txtPointCut"/>
    </aop:config>
</beans>

7、applicationContext文件：用来装配bean

<?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:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/aop
       https://www.springframework.org/schema/aop/spring-aop.xsd">

    <import resource="spring-dao.xml"/>

    <!--装配UserMapperImpl类-->
    <bean id="userMapper" class="com.jason.dao.UserMapperImpl">
        <property name="sqlSessionFactory" ref="sqlSessionFactory"/>
    </bean>
</beans>

8、测试

public class MyTest {
  @Test
  public void test(){
    ApplicationContext context = new ClassPathXmlApplicationContext(
            "applicationContext.xml");
    UserMapper userMapper = context.getBean("userMapper", UserMapper.class);
    List<User> userList = userMapper.selectUser();
    for (User user : userList) {
      System.out.println(user);
    }
  }
}

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