Spring注解式事务解析
Spring注解式事务解析
-
增加一个Advisor
首先往Spring容器新增一个Advisor,BeanFactoryTransactionAttributeSourceAdvisor,它包含了TransactionInterceptor通知和TransactionAttributeSourcePointcut切点。TransactionAttributeSourcePointcut切点实际匹配使用了AnnotationTransactionAttributeSource这个类,它的作用是方法的切点匹配,解析Transactional注解,它尝试从当前类的方法,当前类,父接口方法,父接口查找Transactional注解,有则匹配到。 -
AOP动态代理
当普通bean实例化的时候,Spring通过AbstractAdvisorAutoProxyCreator的其中一个子类进行postProcessAfterInitialization进行AOP这个bean,织入匹配的Advisor,并生成动态代理。动态代理有2种,JdkDynamicAopProxy和ObjenesisCglibAopProxy。 -
拦截过程
方法调用的时候,拿JdkDynamicAopProxy动态代理来讲,被动态代理的bean的公有方法调用会走invoke方法拦截,首先确定当前方法的拦截器链。List<Object> chain = this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);
如果上面的chain为空,不走拦截,否则走拦截责任链
invocation = new ReflectiveMethodInvocation(proxy, target, method, args, targetClass, chain); retVal = invocation.proceed();
-
TransactionInterceptor事务拦截器
内部拿到我们的TransactionInterceptor进行方法调用@Override public Object invoke(final MethodInvocation invocation) throws Throwable { // Work out the target class: may be {@code null}. // The TransactionAttributeSource should be passed the target class // as well as the method, which may be from an interface. Class<?> targetClass = (invocation.getThis() != null ? AopUtils.getTargetClass(invocation.getThis()) : null); // Adapt to TransactionAspectSupport's invokeWithinTransaction... return invokeWithinTransaction(invocation.getMethod(), targetClass, new InvocationCallback() { @Override public Object proceedWithInvocation() throws Throwable { return invocation.proceed(); } }); }
5.创建TransactionInfo对象
他会先获取TransactionAttribute和PlatformTransactionManager,然后调用
```
TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);
```
内部逻辑为拿DataSourceTransactionManager举例,
尝试从ThreadLocal获取ConnectionHolder(包含了一个Connection)
```
protected Object doGetTransaction() {
DataSourceTransactionObject txObject = new DataSourceTransactionObject();
txObject.setSavepointAllowed(isNestedTransactionAllowed());
ConnectionHolder conHolder =
(ConnectionHolder) TransactionSynchronizationManager.getResource(this.dataSource);
txObject.setConnectionHolder(conHolder, false);
return txObject;
}
```
然后判断是不是新事务
```
if (isExistingTransaction(transaction)) {
// Existing transaction found -> check propagation behavior to find out how to behave.
return handleExistingTransaction(definition, transaction, debugEnabled);
}
```
不是新事务,走handleExistingTransaction逻辑,内部会根据我们配置的传递规则做不同的处理,默认的Propagation.REQUIRED就会返回TransactionStatus对象标志为已存在的事务。
是新事务则返回TransactionStatus对象标志为新事务,代码如下:
```
boolean newSynchronization = (getTransactionSynchronization() != SYNCHRONIZATION_NEVER);
DefaultTransactionStatus status = newTransactionStatus(
definition, transaction, true, newSynchronization, debugEnabled, suspendedResources);
doBegin(transaction, definition);
prepareSynchronization(status, definition);
return status;
```
doBegin方法会从dataSource获取一个新连接,并设置到DataSourceTransactionObject的ConnectionHolder字段里,并且设置synchronizedWithTransaction和transactionActive为true代表新事务,然后设置con.setAutoCommit(false),最后设置ThreadLocal值,为当前ConnectionHolder。
```
if (txObject.isNewConnectionHolder()) {
TransactionSynchronizationManager.bindResource(getDataSource(), txObject.getConnectionHolder());
}
```
6.责任链调用下一个拦截器
获取了当前的TransactionInfo开始走下一个拦截器
```
Object retVal = null;
try {
// This is an around advice: Invoke the next interceptor in the chain.
// This will normally result in a target object being invoked.
retVal = invocation.proceedWithInvocation();
}
catch (Throwable ex) {
// target invocation exception
completeTransactionAfterThrowing(txInfo, ex);
throw ex;
}
```
7.提交或回滚
处理完了之后如果抛异常根据匹配规则是否需要回滚,默认对RuntimeException和Error回滚。如果正常返回则调用commitTransactionAfterReturning方法
```
protected void commitTransactionAfterReturning(TransactionInfo txInfo) {
if (txInfo != null && txInfo.hasTransaction()) {
if (logger.isTraceEnabled()) {
logger.trace("Completing transaction for [" + txInfo.getJoinpointIdentification() + "]");
}
txInfo.getTransactionManager().commit(txInfo.getTransactionStatus());
}
}
```
进行commit,最后调用doCleanupAfterCompletion方法,清空ThreadLocal,设置con.setAutoCommit(true),并关闭连接。