自定义事务

Spring的开启事务管理主要是通过@EnableTransactionManagement注解来实现的。 查看源码就会发现，这个注解主要是注入了两个类InfrastructureAdvisorAutoProxyCreator和BeanFactoryTransactionAttributeSourceAdvisor，而且这两个类是通过其他的Configure类导入的。
InfrastructureAdvisorAutoProxyCreator继承自AbstractAutoProxyCreator，自定义Aop里介绍过这个类，主要是读取Advisor类，并对符合的bean进行二次代理。
BeanFactoryTransactionAttributeSourceAdvisor就是被扫描的Advisor类。这个类会扫面被Transactional注释的类的方法，并提供TransactionInterceptor，来代理被注释的方法。

完整的代码参考Github，这里介绍一下几个关键的类。
自定义的注解，简便起见注解的属性就不列出来了，跟Transactional的属性一样。

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface MyTransactional {
....
}

DataSource和dao层，简便起见，用的内存式数据库h2，dao层用的是mybatis。

@Bean
public SqlSessionFactoryBean sqlSessionFactoryBean() {
SqlSessionFactoryBean sqlSessionFactoryBean = new SqlSessionFactoryBean();
sqlSessionFactoryBean.setDataSource(dataSource());
return sqlSessionFactoryBean;
}

@Bean
public MapperScannerConfigurer mapperScannerConfigurer() {
MapperScannerConfigurer mapperScannerConfigurer = new MapperScannerConfigurer();
mapperScannerConfigurer.setBasePackage("org.wcong.test.spring.mybatis.mapper");
return mapperScannerConfigurer;
}

@Bean
public DataSource dataSource() {
EmbeddedDatabaseBuilder embeddedDatabaseBuilder = new EmbeddedDatabaseBuilder();
return embeddedDatabaseBuilder.setType(EmbeddedDatabaseType.H2).build();
}

定义dao方法。

public interface DbTest {
@Select("select count(*) from db_test")
int count();
@Insert("insert into db_test(id,date,content) values(#{id},now(),#{content})")
@MyTransactional
int add(TestModel testModel);
@Insert("create table db_test(id int,date time,content varchar)")
int createTable();
}

注入transactionManager。

@Bean(name = "transactionManager")
public PlatformTransactionManager transactionManager() {
DataSourceTransactionManager transactionManager = new DataSourceTransactionManager();
transactionManager.setDataSource(dataSource());
return transactionManager;
}

InfrastructureAdvisorAutoProxyCreator是直接使用Spring内置的类。

@Bean
@Order(Ordered.HIGHEST_PRECEDENCE)
public InfrastructureAdvisorAutoProxyCreator advisorAutoProxyCreator() {
return new InfrastructureAdvisorAutoProxyCreator();
}

BeanFactoryTransactionAttributeSourceAdvisor需要扫描自定义的注解，并嵌入到方法执行的前后，就需要自己定义了。 其中MySpringTransactionAnnotationParser继承自Spring内置的SpringTransactionAnnotationParser类，重写了扫描注解的方法。 MyTransactionInterceptor则继承了Spring内置的TransactionInterceptor重写了invoke方法，在事务方法开始的前后输出了部分信息。MyProxyTransactionManagementConfiguration则是参考的Spring的注入方式，组装BeanFactoryTransactionAttributeSourceAdvisor并注入相关的Bean。

public static class MySpringTransactionAnnotationParser extends SpringTransactionAnnotationParser {
@Override
public TransactionAttribute parseTransactionAnnotation(AnnotatedElement ae) {
AnnotationAttributes attributes = AnnotatedElementUtils
.getMergedAnnotationAttributes(ae, MyTransactional.class);
if (attributes != null) {
return parseTransactionAnnotation(attributes);
} else {
return null;
}
}
public TransactionAttribute parseTransactionAnnotation(MyTransactional ann) {
return parseTransactionAnnotation(AnnotationUtils.getAnnotationAttributes(ann, false, false));
}
}
public static class MyTransactionInterceptor extends TransactionInterceptor {
@Override
public Object invoke(final MethodInvocation invocation) throws Throwable {
System.out.println("transaction method :" +
invocation.getMethod().getDeclaringClass().getName() + "." + invocation.getMethod().getName());
Object object = super.invoke(invocation);
System.out.println(invocation.getMethod().getName() + " result :" + object);
return object;
}
}
@Configuration
public static class MyProxyTransactionManagementConfiguration {
protected PlatformTransactionManager txManager;
@Bean(name = TransactionManagementConfigUtils.TRANSACTION_ADVISOR_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public BeanFactoryTransactionAttributeSourceAdvisor transactionAdvisor() {
BeanFactoryTransactionAttributeSourceAdvisor advisor = new BeanFactoryTransactionAttributeSourceAdvisor();
advisor.setTransactionAttributeSource(transactionAttributeSource());
advisor.setAdvice(transactionInterceptor());
advisor.setOrder(Ordered.LOWEST_PRECEDENCE);
return advisor;
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionAttributeSource transactionAttributeSource() {
return new AnnotationTransactionAttributeSource(new MySpringTransactionAnnotationParser());
}
@Bean(name = TransactionManagementConfigUtils.TRANSACTIONAL_EVENT_LISTENER_FACTORY_BEAN_NAME)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionalEventListenerFactory transactionalEventListenerFactory() {
return new TransactionalEventListenerFactory();
}
@Autowired(required = false)
void setConfigurers(Collection<TransactionManagementConfigurer> configurers) {
if (CollectionUtils.isEmpty(configurers)) {
return;
}
if (configurers.size() > 1) {
throw new IllegalStateException("Only one TransactionManagementConfigurer may exist");
}
TransactionManagementConfigurer configurer = configurers.iterator().next();
this.txManager = configurer.annotationDrivenTransactionManager();
}
@Bean
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public TransactionInterceptor transactionInterceptor() {
TransactionInterceptor interceptor = new MyTransactionInterceptor();
interceptor.setTransactionAttributeSource(transactionAttributeSource());
if (this.txManager != null) {
interceptor.setTransactionManager(this.txManager);
}
return interceptor;
}
}

观察程序的日志就会发现在Spring加载了被MyTransactional的方法，并放到了事务中执行。同时在方法执行前后输出了方法的一些信息。 

结语

Spring的事务管理是建立在Aop之上的，借用了Advisor和Interceptor的很多方法。扩展一下，还可以通过自定义注解，对相应的方法进行代理