解密@Transactional和@Async传播有效性

微信公众号文章列表：关注公众号（coding_song）阅读更清晰

微信原文地址：https://mp.weixin.qq.com/s/fx1tDzezuE3NWqGpIOU7og

现象

Controller类中调用Service类中标有@Async或@Transactional注解的方法，此方法上的@Async或@Transactional会生效，而在Service类中A方法直接调用标有@Async或@Transactional注解的B方法，B方法上的@Async或@Transactional注解不会生效；如果A方法中重新通过动态代理生成一个Service Bean类，再通过这个新生成的Bean调用B方法，则B方法上的@Async或@Transactional注解将会生效；当B方法上同时含有@Async和@Transactional注解时，只会有一个注解生效，@Async会生效而@Transactional不会生效

原因

Spring项目中，A类调用B类的方法，是A类通过CglibAopProxy动态代理来生成B类，而B类中方法之间的调用，是直接调用其方法，不会再通过动态代理重新生成一个相同的B类，再调用目标方法；CglibAopProxy动态代理生成B类时，会获取到B类目标方法上面的所有注解（@Async或@Transactional等），并获取这些注解的拦截器和拦截器切面（AsyncAnnotationAdvisor和BeanFactoryTransactionAttributeSourceAdvisor），然后判断这些切面的是否是PointcutAdvisor的子类，方法是否匹配注解方法匹配器AnnotataionMethodMatcher，如果是，则获取这个拦截器切面对应的方法拦截器（AnnotationAsyncExceutionInterceptor或TransactionInterceptor），获取到这些方法拦截器后（如果有多个），只取第一个拦截器，如果第一个是TransactionInterceptor拦截器，则会为该方法开启一个事物；如果第一个是AnnotationAsyncExceutionInterceptor，则会为这个方法创建一个线程，让此方法运行在新建的线程中，由此起到了异步执行的作用

样例代码

Controller层代码

1. @RestController

2. publicclassTestController{

3.  

4.    @Autowired

5.    privateTestService testService;

6.  

7.    @GetMapping("/test")

8.    publicvoid test(){

9.        testService.getId();

10.    }

11.  

12. }

服务层代码及@Async和@Transactional生效说明

1. @Service

2. publicclassTestServiceImplimplementsTestService,ApplicationContextAware{

3.  

4.    privateApplicationContext applicationContext;

5.  

6.    @Autowired

7.    privateTestService testService;

8.  

9.    @Override

10.    publicvoid setApplicationContext(ApplicationContext applicationContext)throwsBeansException{

11.        this.applicationContext = applicationContext;

12.    }

13.  

14.    /**

15.     * 当Controller层调用此方法时，@Transactional生效，将会开启一个事物

16.     * @return

17.     */

18.    @Override

19.    @Transactional(rollbackFor =RuntimeException.class)

20.    publicInteger getId(){

21.        TestService testService =(TestService) applicationContext.getBean("testServiceImpl");

22.        Integer integer = testService.testTransactional();

23.        return integer;

24.    }

25.  

26.    /**

27.     * 1）本类中，如果是通过applicationContext.getBean创建一个TestService后，再调用此方法，

28.     * 由于方法上同时有@Async和@Transactional注解，获取到这两个注解的拦截器后，只会取第一个拦截器进行后续的操作，

29.     * 所以@Async会生效，而@Transactional不会生效

30.     * 2）如果是直接调testTransactional()方法，而不是从新生成一个新的TestService Bean来调用此方法，

31.     * 则此类上的@Async和@Transactional注解都不会生效，因为不会走AOP动态代理CglibAopProxy，

32.     * 而@Async和@Transactional注解生效的实现，是在CglibAopProxy中实现的

33.     * @return

34.     */

35.    @Override

36.    @Async

37.    @Transactional(rollbackFor =RuntimeException.class)

38.    publicInteger testTransactional(){

39.        Integer test = test();

40.        return test;

41.    }

42.  

43.    /**

44.     * 此方法上的@Async和@Transactional都不会生效，因为在testTransactional()是直接调用此方法

45.     * @return

46.     */

47.    @Async

48.    @Transactional(rollbackFor =RuntimeException.class)

49.    privateInteger test(){

50.        return10;

51.    }

52. }

源码分析

在Controller类中注入Service时，是通过Cglib动态代理生成的Service，所以当Controller类调用Service中的方法时，会调用CglibAopProxy内部类DynamicAdvisedInterceptor的intercept()方法

1. @Override

2. @Nullable

3. publicObject intercept(Object proxy,Method method,Object[] args,MethodProxy methodProxy)throwsThrowable{

4.    Object oldProxy =null;

5.    boolean setProxyContext =false;

6.    Object target =null;

7.    TargetSource targetSource =this.advised.getTargetSource();

8.    try{

9.        if(this.advised.exposeProxy){

10.            // Make invocation available if necessary.

11.            oldProxy =AopContext.setCurrentProxy(proxy);

12.            setProxyContext =true;

13.        }

14.        // Get as late as possible to minimize the time we "own" the target, in case it comes from a pool...

15.        target = targetSource.getTarget();

16.        Class<?> targetClass =(target !=null? target.getClass():null);

17.        //获取方法上的所有注解的切面拦截器

18.        List<Object> chain =this.advised.getInterceptorsAndDynamicInterceptionAdvice(method, targetClass);

19.        Object retVal;

20.        //当在方法上没有获取到相应注解的拦截器时，直接进入方法执行相应逻辑

21.        if(chain.isEmpty()&&Modifier.isPublic(method.getModifiers())){

22.            // We can skip creating a MethodInvocation: just invoke the target directly.

23.            // Note that the final invoker must be an InvokerInterceptor, so we know

24.            // it does nothing but a reflective operation on the target, and no hot

25.            // swapping or fancy proxying.

26.            Object[] argsToUse =AopProxyUtils.adaptArgumentsIfNecessary(method, args);

27.            retVal = methodProxy.invoke(target, argsToUse);

28.        }else{

29.            // 获取当方法拦截器后，通过反射调用具体的拦截器方法

30.                        //接下来先调用ReflectiveMethodInvocation的proceed方法

31.            retVal =newCglibMethodInvocation(proxy, target, method, args, targetClass, chain, methodProxy).proceed();

32.        }

33.        retVal = processReturnType(proxy, target, method, retVal);

34.        return retVal;

35.    }

36.    //省略finally代码

37. }

ReflectiveMethodInvocation.proceed方法只获取拦截器切面列表中的第一个拦截器切面，执行相应的拦截器逻辑

1. @Override

2. @Nullable

3. publicObject proceed()throwsThrowable{

4.    //  We start with an index of -1 and increment early.

5.    if(this.currentInterceptorIndex ==this.interceptorsAndDynamicMethodMatchers.size()-1){

6.        return invokeJoinpoint();

7.    }

8.  

9.    //如果方法上有多个拦截器或拦截器切面，只取第一个拦截器或拦截器切面

10.    Object interceptorOrInterceptionAdvice =

11.        this.interceptorsAndDynamicMethodMatchers.get(++this.currentInterceptorIndex);

12.    if(interceptorOrInterceptionAdvice instanceofInterceptorAndDynamicMethodMatcher){

13.        // Evaluate dynamic method matcher here: static part will already have

14.        // been evaluated and found to match.

15.        InterceptorAndDynamicMethodMatcher dm =

16.                (InterceptorAndDynamicMethodMatcher) interceptorOrInterceptionAdvice;

17.        Class<?> targetClass =(this.targetClass !=null?this.targetClass :this.method.getDeclaringClass());

18.        if(dm.methodMatcher.matches(this.method, targetClass,this.arguments)){

19.            return dm.interceptor.invoke(this);

20.        }else{

21.            // Dynamic matching failed.

22.            // Skip this interceptor and invoke the next in the chain.

23.            return proceed();

24.        }

25.    }

26.    else{

27.        // It's an interceptor, so we just invoke it: The pointcut will have

28.        // been evaluated statically before this object was constructed.

29.        //调用具体的拦截器

30.        return((MethodInterceptor) interceptorOrInterceptionAdvice).invoke(this);

31.    }

32. }

如果第一个拦截器切面是TransactionInterceptor，则调用TransactionInterceptor相关的方法，执行相应的逻辑，开启事务等

1. @Override

2. @Nullable

3. publicObject invoke(MethodInvocation invocation)throwsThrowable{

4.    // Work out the target class: may be {@code null}.

5.    // The TransactionAttributeSource should be passed the target class

6.    // as well as the method, which may be from an interface.

7.    Class<?> targetClass =(invocation.getThis()!=null?AopUtils.getTargetClass(invocation.getThis()):null);

8.  

9.    // Adapt to TransactionAspectSupport's invokeWithinTransaction...

10.    //适配TransactionAspectSupport的invokeWithinTransaction方法

11.    return invokeWithinTransaction(invocation.getMethod(), targetClass, invocation::proceed);

12. }

13.  

14. @Nullable

15. protectedObject invokeWithinTransaction(Method method,@NullableClass<?> targetClass,

16.        finalInvocationCallback invocation)throwsThrowable{

17.  

18.    // If the transaction attribute is null, the method is non-transactional.

19.    TransactionAttributeSource tas = getTransactionAttributeSource();

20.    finalTransactionAttribute txAttr =(tas !=null? tas.getTransactionAttribute(method, targetClass):null);

21.    finalPlatformTransactionManager tm = determineTransactionManager(txAttr);

22.    finalString joinpointIdentification = methodIdentification(method, targetClass, txAttr);

23.  

24.    if(txAttr ==null||!(tm instanceofCallbackPreferringPlatformTransactionManager)){

25.        // Standard transaction demarcation with getTransaction and commit/rollback calls.

26.        //调用事务管理器的getTransaction和commit/rollback方法，获取一个事务对象，并开启事物

27.        TransactionInfo txInfo = createTransactionIfNecessary(tm, txAttr, joinpointIdentification);

28.        Object retVal =null;

29.        try{

30.            // This is an around advice: Invoke the next interceptor in the chain.

31.            // This will normally result in a target object being invoked.

32.            //调用目标类的方法

33.            retVal = invocation.proceedWithInvocation();

34.        }

35.        catch(Throwable ex){

36.            // target invocation exception

37.            completeTransactionAfterThrowing(txInfo, ex);

38.            throw ex;

39.        }

40.        finally{

41.            //执行目标方法后，关闭事务，清除事物对象

42.            cleanupTransactionInfo(txInfo);

43.        }

44.        //结果返回后提交事物状态等信息

45.        commitTransactionAfterReturning(txInfo);

46.        return retVal;

47.    }else{

48.        //省略其他代码

49.    }

50. }

51. /**

52. * 根据给定的事务参数创建一个事物.

53. * @see #getTransactionAttributeSource()

54. */

55. protectedTransactionInfo createTransactionIfNecessary(@NullablePlatformTransactionManager tm,

56.        @NullableTransactionAttribute txAttr,finalString joinpointIdentification){

57.  

58.    // If no name specified, apply method identification as transaction name.

59.    if(txAttr !=null&& txAttr.getName()==null){

60.        txAttr =newDelegatingTransactionAttribute(txAttr){

61.            @Override

62.            publicString getName(){

63.                return joinpointIdentification;

64.            }

65.        };

66.    }

67.  

68.    TransactionStatus status =null;

69.    if(txAttr !=null){

70.        if(tm !=null){

71.            //开启事物

72.            status = tm.getTransaction(txAttr);

73.        }

74.        else{

75.            if(logger.isDebugEnabled()){

76.                logger.debug("Skipping transactional joinpoint ["+ joinpointIdentification +

77.                        "] because no transaction manager has been configured");

78.            }

79.        }

80.    }

81.    //准备事物对象信息

82.    return prepareTransactionInfo(tm, txAttr, joinpointIdentification, status);

83. }

84. /**

85. * 委托doGetTransaction方法，isExistingTransaction判断条件和doBegin方法处理事务传播行为

86. * This implementation handles propagation behavior. Delegates to

87. * {@code doGetTransaction}, {@code isExistingTransaction}

88. * and {@code doBegin}.

89. * @see #doGetTransaction

90. * @see #isExistingTransaction

91. * @see #doBegin

92. */

93. @Override

94. publicfinalTransactionStatus getTransaction(@NullableTransactionDefinition definition)throwsTransactionException{

95.    Object transaction = doGetTransaction();

96.  

97.    // Cache debug flag to avoid repeated checks.

98.    boolean debugEnabled = logger.isDebugEnabled();

99.  

100.    if(definition ==null){

101.        // Use defaults if no transaction definition given.

102.        definition =newDefaultTransactionDefinition();

103.    }

104.    //如果已经有事务存在，直接处理已存在的事务

105.    if(isExistingTransaction(transaction)){

106.        // Existing transaction found -> check propagation behavior to find out how to behave.

107.        return handleExistingTransaction(definition, transaction, debugEnabled);

108.    }

109.  

110.    // Check definition settings for new transaction.

111.    if(definition.getTimeout()<TransactionDefinition.TIMEOUT_DEFAULT){

112.        thrownewInvalidTimeoutException("Invalid transaction timeout", definition.getTimeout());

113.    }

114.  

115.    // No existing transaction found -> check propagation behavior to find out how to proceed.

116.    if(definition.getPropagationBehavior()==TransactionDefinition.PROPAGATION_MANDATORY){

117.        thrownewIllegalTransactionStateException(

118.                "No existing transaction found for transaction marked with propagation 'mandatory'");

119.    }

120.    elseif(definition.getPropagationBehavior()==TransactionDefinition.PROPAGATION_REQUIRED ||

121.            definition.getPropagationBehavior()==TransactionDefinition.PROPAGATION_REQUIRES_NEW ||

122.            definition.getPropagationBehavior()==TransactionDefinition.PROPAGATION_NESTED){

123.        SuspendedResourcesHolder suspendedResources = suspend(null);

124.        if(debugEnabled){

125.            logger.debug("Creating new transaction with name ["+ definition.getName()+"]: "+ definition);

126.        }

127.        try{

128.            boolean newSynchronization =(getTransactionSynchronization()!= SYNCHRONIZATION_NEVER);

129.            DefaultTransactionStatus status = newTransactionStatus(

130.                    definition, transaction,true, newSynchronization, debugEnabled, suspendedResources);

131.            //开启事务

132.            doBegin(transaction, definition);

133.            prepareSynchronization(status, definition);

134.            return status;

135.        }

136.        catch(RuntimeException|Error ex){

137.            resume(null, suspendedResources);

138.            throw ex;

139.        }

140.    }

141.    else{

142.        // Create "empty" transaction: no actual transaction, but potentially synchronization.

143.        if(definition.getIsolationLevel()!=TransactionDefinition.ISOLATION_DEFAULT && logger.isWarnEnabled()){

144.            logger.warn("Custom isolation level specified but no actual transaction initiated; "+

145.                    "isolation level will effectively be ignored: "+ definition);

146.        }

147.        boolean newSynchronization =(getTransactionSynchronization()== SYNCHRONIZATION_ALWAYS);

148.        return prepareTransactionStatus(definition,null,true, newSynchronization, debugEnabled,null);

149.    }

150. }

 

如果第一个拦截器切面是AsyncExecutionInterceptor，则会获取一个任务执行器，再创建一个任务，然后从线程池ThreadPoolExecutor中获取一个线程来执行这个任务

1. @Override

2. @Nullable

3. publicObject invoke(finalMethodInvocation invocation)throwsThrowable{

4.    Class<?> targetClass =(invocation.getThis()!=null?AopUtils.getTargetClass(invocation.getThis()):null);

5.    Method specificMethod =ClassUtils.getMostSpecificMethod(invocation.getMethod(), targetClass);

6.    finalMethod userDeclaredMethod =BridgeMethodResolver.findBridgedMethod(specificMethod);

7.    //获取一个异步任务执行器

8.    AsyncTaskExecutor executor = determineAsyncExecutor(userDeclaredMethod);

9.    if(executor ==null){

10.        thrownewIllegalStateException(

11.                "No executor specified and no default executor set on AsyncExecutionInterceptor either");

12.    }

13.    //创建一个任务

14.    Callable<Object> task =()->{

15.        try{

16.            Object result = invocation.proceed();

17.            if(result instanceofFuture){

18.                return((Future<?>) result).get();

19.            }

20.        }

21.        catch(ExecutionException ex){

22.            handleError(ex.getCause(), userDeclaredMethod, invocation.getArguments());

23.        }

24.        catch(Throwable ex){

25.            handleError(ex, userDeclaredMethod, invocation.getArguments());

26.        }

27.        returnnull;

28.    };

29.    //最终会从ThreadPoolExecutor获取一个线程来提交需要执行的任务

30.    return doSubmit(task, executor, invocation.getMethod().getReturnType());

31. }

32. /**

33. * AsyncExecutionAspectSupport.doSubmit()

34. * 提交任务

35. */

36. @Nullable

37. protectedObject doSubmit(Callable<Object> task,AsyncTaskExecutor executor,Class<?> returnType){

38.    if(CompletableFuture.class.isAssignableFrom(returnType)){

39.        returnCompletableFuture.supplyAsync(()->{

40.            try{

41.                return task.call();

42.            }

43.            catch(Throwable ex){

44.                thrownewCompletionException(ex);

45.            }

46.        }, executor);

47.    }

48.    elseif(ListenableFuture.class.isAssignableFrom(returnType)){

49.        return((AsyncListenableTaskExecutor) executor).submitListenable(task);

50.    }

51.    elseif(Future.class.isAssignableFrom(returnType)){

52.        return executor.submit(task);

53.    }

54.    else{

55.        //继续提交任务

56.        executor.submit(task);

57.        returnnull;

58.    }

59. }

60. /**

61. * ThreadPoolTaskExecutor.submit() 从线程池中获取一个线程来执行任务

62. */

63. public<T>Future<T> submit(Callable<T> task){

64.    ThreadPoolExecutor executor =this.getThreadPoolExecutor();

65.  

66.    try{

67.        return executor.submit(task);

68.    }catch(RejectedExecutionException var4){

69.        thrownewTaskRejectedException("Executor ["+ executor +"] did not accept task: "+ task, var4);

70.    }

71. }

 

解决方案

在Service中A方法调用B方法，要使B方法上的@Async或@Transcational注解生效，可在A方法中通过ApplicationContext.getBean()来从新获取一个新的Service对象，代码实现如下

1. @Service

2. publicclassTestServiceImplimplementsTestService,ApplicationContextAware{

3.    //省略其他代码

4.    @Override

5.    @Transactional(rollbackFor =RuntimeException.class)

6.    publicInteger getId(){

7.        TestService testService =(TestService) applicationContext.getBean("testServiceImpl");

8.        Integer integer = testService.testTransactional();

9.        return integer;

10.    }

11.  

12.    @Override

13.    @Transactional(rollbackFor =RuntimeException.class)

14.    publicInteger testTransactional(){

15.        Integer test = test();

16.        return test;

17.    }

18. }

上述testTransactional()方法上的@Transactional将生效