十三、声明式事务
1. 回顾事务
- 把一组业务当成一个业务来做。要么都成功，要么都失败
- 事务在项目开发中，十分重要，涉及到数据的一致性问题
- 确保完整性和一致性
事务的ACID原则：
- 原子性
- 一致性
- 隔离性
- 多个业务可能同时操作同一个资源，防止数据损坏
- 持久性
- 事务一旦提交，无论系统发生什么问题，结果都不会再影响，被持久化的写到存储器中
2. 一个案例
我们把前面的一个案例给拿下来
为了防止错误，这里再把代码以及步骤整一下：
- pom.xml导入包
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <parent> <artifactId>Spring-Study</artifactId> <groupId>com.hxl</groupId> <version>1.0-SNAPSHOT</version> </parent> <modelVersion>4.0.0</modelVersion> <artifactId>spring-11-transaction</artifactId> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.26</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.7</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.3.11</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-jdbc</artifactId> <version>5.3.11</version> </dependency> <dependency> <groupId>org.aspectj</groupId> <artifactId>aspectjweaver</artifactId> <version>1.9.7</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> <version>2.0.6</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.20</version> </dependency> </dependencies> <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> </resource> </resources> </build> </project>
2.实体类
package com.hxl.pojo; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; @Data @AllArgsConstructor @NoArgsConstructor public class User { private int id; private String name; private String pwd; }
3.接口
package com.hxl.mapper; import com.hxl.pojo.User; import java.util.List; public interface UserMapper { public List<User> selectUser(); //添加一个用户 public int addUser(User user); //删除一个用户 public int deleteUser(int id); }
4.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"> <!--核心配置文件--> <configuration> <!--别名管理--> <typeAliases> <package name="com.hxl.pojo"/> </typeAliases> <!--设置--> <!--比如说日志开启--> <!--<environments default="development"> <environment id="development"> <!–事务管理–> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments>--> <!--每一个Mapper.xml都需要在Mybatis核心配置文件中注册--> <!-- <mappers> <!–用class的话需要mapper的两个名字相同并且在同一个包下–> <mapper resource="com/hxl/mapper/UserMapper.xml"/> </mappers>--> </configuration>
5.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" xmlns:aop="http://www.springframework.org/schema/aop" 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 http://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop.xsd"> <!--DataSource:使用Spring的数据源替换Mybatis的配置:c3p0 dbcp druid 这里使用Spring提供的JDBC. 这里使用了之后我们就可以把mybatis-config.xml中的去掉了 --> <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&useUnicode=true&characterEncoding=UTF-8"/> <property name="username" value="root"/> <property name="password" value="123456"/> </bean> <!--sqlSessionFactory--> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <!--绑定上方所写数据源--> <property name="dataSource" ref="dataSource"/> <!--绑定mybatis配置文件--> <property name="configLocation" value="classpath:mybatis-config.xml"/> <!--这样的话原来的注册mapper也就不需要了--> <property name="mapperLocations" value="classpath:com/hxl/mapper/*.xml"/> </bean> <!--SqlSessionTemplate就是我们使用的sqlSession--> <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate"> <!--只能使用构造器注入sqlSessionFactory，因为它没有set方法--> <constructor-arg index="0" ref="sqlSessionFactory"/> </bean> </beans>
6.UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="com.hxl.mapper.UserMapper"> <!--resultType:主要用于从数据库中提取数据--> <select id="selectUser" resultType="user"> select * from user </select> <insert id="addUser" parameterType="user"> insert into user(id,name,pwd) values (#{id},#{name},#{pwd}) </insert> <delete id="deleteUser" parameterType="int"> deletes from user where id=#{id} </delete> </mapper>
7.UserMapperImpl
package com.hxl.mapper; import com.hxl.pojo.User; import org.mybatis.spring.SqlSessionTemplate; import org.mybatis.spring.support.SqlSessionDaoSupport; import java.util.List; public class UserMapperImpl extends SqlSessionDaoSupport implements UserMapper{ public List<User> selectUser() { User user = new User(5, "老五", "123456"); UserMapper mapper = getSqlSession().getMapper(UserMapper.class); mapper.addUser(user); mapper.deleteUser(5); return mapper.selectUser(); } public int addUser(User user) { return getSqlSession().getMapper(UserMapper.class).addUser(user); } public int deleteUser(int id) { return getSqlSession().getMapper(UserMapper.class).deleteUser(id); } }
8.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" xmlns:context="http://www.springframework.org/schema/context" xmlns:aop="http://www.springframework.org/schema/aop" 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 http://www.springframework.org/schema/aop https://www.springframework.org/schema/aop/spring-aop.xsd"> <import resource="spring-dao.xml"/> <!--注入到spring中--> <bean id="userMapper" class="com.hxl.mapper.UserMapperImpl"> <property name="sqlSessionFactory" ref="sqlSessionFactory"/> </bean> </beans>
9.测试
import com.hxl.mapper.UserMapper; import com.hxl.pojo.User; import org.junit.Test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MyTest { @Test public void test(){ ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); UserMapper userMapper = context.getBean("userMapper", UserMapper.class); for (User user : userMapper.selectUser()) { System.out.println(user); } } }
这里是为了重现数据库的错误：我们编写的delete语句是错误的，我们运行发现数据库中加入了增加的数据。这个是不对的，因为我们的删除语句失败了，结果插进去了，不符合我们的原则。ACID原则
3.Spring中的事务管理
- 声明式事务：AOP
- 编程式事务：需要在代码中，进行事务的管理
在spring-dao中增加下面这段代码就可以实现上面的问题，delete报错，add也不会加入
<!--结合aop实现事务的织入：需要找到一个切入点或切面这个东西--> <!--1.配置事务通知：--> <tx:advice id="txAdvice" transaction-manager="transactionManager"> <!--给方法配置事务； 配置事务的传播特性：new propagation="REQUIRED"默认就是它，可以不写 --> <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> <!--2.配置事务切入--> <aop:config> <aop:pointcut id="txPointCut" expression="execution(* com.hxl.mapper.*.*(..))"/> <aop:advisor advice-ref="txAdvice" pointcut-ref="txPointCut"/> </aop:config>
思考:
为什么需要事务？
- 如果不配置事务，可能存在数据提交不一致的情况
- 如果我们不在spring中去配置声明式事务，我们就需要在代码中手动配置事务，
- 事务在开发中十分重要，涉及到数据的一致性和完整性问题。
