使用 AspectJ 样式 Spring AOP 的请求作用域 bean 的空指针异常（@Around 建议使用 @Transactional webservice 方法）

Question

我正在使用 Spring 3.1.0.RC1。我有一个基于 Apache CXF 的 Web 服务。我试图为每个 @Transactional 注释的服务方法提供建议。

我有一些关于周围建议的方面。在该方法内部，我将数据存储到请求范围的事务负载 bean 中。后来我在另一个单例作用域 bean 中请求此有效负载中的 uuid。结果是空指针异常。

Caused by: java.lang.RuntimeException: java.lang.NullPointerException
    at com.spp.mui.jaxws.service.virtual._0_1.VirtualWebService.postOfferSet(VirtualWebService.java:209)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:309)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
    at com.spp.mui.aop.tx.NewAgeTransactionLoggingAspect.logTransaction(NewAgeTransactionLoggingAspect.java:85)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:161)
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:80)
    at com.spp.mui.aop.ws.TraceWebServiceMethodAspect.invoke(TraceWebServiceMethodAspect.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:621)
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:610)
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:65)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
    at $Proxy95.postOfferSet(Unknown Source)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:173)
    at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:89)
    ... 49 more
Caused by: java.lang.NullPointerException
    at com.spp.mui.jaxws.agent.WSResponseAgent.getResponse(WSResponseAgent.java:28)
    at com.spp.mui.jaxws.agent.WSResponseAgent.getResponse(WSResponseAgent.java:18)
    at com.spp.mui.jaxws.handler.offer.PostVirtualOffersHandler.handle(PostVirtualOffersHandler.java:58)
    at com.spp.mui.jaxws.service.virtual._0_1.VirtualWebService.postOfferSet(VirtualWebService.java:205)
    ... 88 more

那么这个堆栈跟踪中发生了什么？

调用了 Web 服务方法（即 postOfferSet）。该方法是由带有 @Around 切入点的方面建议的。该方法也带有 @Transactional 注释。

更新我已经将原始配置更新为基于Java配置。无论是 XML 配置还是 Java 配置，我都遇到了同样的问题。我的 Java 配置是当前正在使用的配置，也是我希望帮助诊断的配置。请向下滚动（向前跳）查看下面的 Java 配置。 （对于其他刚接触这篇文章的人，请继续阅读）。

我的方面配置看起来有点像

 <aop:aspectj-autoproxy />

 <bean id="newAgeTxLoggingAspect" class="com.spp.mui.aop.tx.NewAgeTransactionLoggingAspect">
    <property name="transactionLogService" ref="txLogServiceEngine" />
    <property name="securable" ref="securityAgent" />
    <property name="loggableTransactionToken" ref="loggableTransactionToken" />
    <property name="logQuery" value="${newAgeTxLoggingAspect.logQuery}" />
    <property name="logReply" value="${newAgeTxLoggingAspect.logReply}" />
    <property name="logSubmit" value="${newAgeTxLoggingAspect.logSubmit}" />
    <property name="maxReplySize" value="${newAgeTxLoggingAspect.maxReplySize}" />
    <property name="maxRequestSize" value="${newAgeTxLoggingAspect.maxRequestSize}" />
    <property name="order" value="5" />
</bean>

前面提到的 loggableTransactionToken 是请求范围的。

这是它的 bean def

<!-- 
    Request scoped bean that allows LoggableTransaction instances to be created and accessed on a single-thread of execution
    Consult http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-factory-scopes-other-injection 
-->
<bean id="loggableTransactionToken" class="com.spp.mui.commons.spring.LoggableTransactionToken" scope="request">
    <aop:scoped-proxy proxy-target-class="false"/>
</bean>

前面提到的 Web 服务方法委托给 Handler

这是 Handler 的一个片段

 @Override
public ConfirmationType handle(OfferSetType request) {
    // step 1: convert from JAXB type to domain objects
    List<MktVirtualOffer> candidateOffers = codecService.convert(request, List.class);
    ...
    // step 4: get response -- response encapsulates transaction id
    return responder.getResponse();
}

请注意，Handler 使用了 Responder？

这是响应程序（又名 WSResponseAgent）的片段，

@Override
public ConfirmationType getResponse() {
    ConfirmationType response = new ConfirmationType();
    LoggableTransaction lt = token.getToken();
    response.setTransactionID(lt.getUuid());
    logger.debug(ReflectUtil.toString(lt));
    return response;
}

希望我已经提供了足够的信息来帮助您调查为什么我会收到 NPE？

更新这是Java配置和附加实现

AOP配置

@Configuration
@EnableAspectJAutoProxy
@Import(value = { LoggingConfig.class, AuthConfig.class })
public class AopConfig {

@Resource
private Environment env;

@Resource
private LoggingConfig loggingConfig;

@Resource
private AuthConfig authConfig;

/* Consult
 *   static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/transaction.html#transaction-declarative-applying-more-than-just-tx-advice
 *   and http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/aop.html#aop-ataspectj-advice-ordering
 */

@Bean
public NewAgeTransactionLoggingAspect txLoggingAspect() {
    NewAgeTransactionLoggingAspect aspect = new NewAgeTransactionLoggingAspect();
    aspect.setEnvironment(env);
    aspect.setLoggableTransactionToken(loggingConfig.loggableTxToken());
    aspect.setSecurable(authConfig.securable());
    aspect.setTransactionLogService(loggingConfig.txLogService());
    aspect.setLogQuery(Boolean.valueOf(env.getProperty("newAgeTxLoggingAspect.logQuery", Boolean.toString(true))));
    aspect.setLogReply(Boolean.valueOf(env.getProperty("newAgeTxLoggingAspect.logReply", Boolean.toString(true))));
    aspect.setLogSubmit(Boolean.valueOf(env.getProperty("newAgeTxLoggingAspect.logSubmit", Boolean.toString(true))));
    aspect.setMaxRequestSize(Integer.valueOf(env.getProperty("newAgeTxLoggingAspect.maxRequestSize", "100000000")));
    aspect.setMaxReplySize(Integer.valueOf(env.getProperty("newAgeTxLoggingAspect.maxReplySize", "100000000")));
    aspect.setOrder(Integer.valueOf(env.getProperty("newAgeTxLoggingAspect.order", "5")));
    return aspect;
}


}

这是负责设置NewAgeTransactionLoggingService和LoggableTransactionToken的配置的片段

@Bean
public TransactionLogService txLogService() {
    HibernateTransactionLogService service = new HibernateTransactionLogService();
    service.setLogParameters(Boolean.valueOf(Boolean.toString(true)));
    service.setTimeDispatcher(timeConfig.timeDispatcher());
    service.setSessionFactory(sessionFactory);
    return service;
}


/**
 * @return <p>Request scoped bean that allows LoggableTransaction instances to be created and accessed on a request.<br/>
 * Consult <a href="http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-factory-scopes-other-injection">Bean Factory Scopes</a></p>
 */
@Bean
@Scope(value="request", proxyMode=ScopedProxyMode.INTERFACES)
public Token<LoggableTransaction> loggableTxToken() {
    // XXX Is this is the correct way to specify a request-scoped bean?
    LoggableTransactionToken token = new LoggableTransactionToken();
    return token;
}

这是带有@Around建议的方面的方法。

@Around("com.spp.mui.aop.Advisables.transactionLoggable()")
public Object logTransaction(ProceedingJoinPoint pjp) throws Throwable {
    // Prepare to log the execution time of the method call..
    long t0 = 0;
    t0 = System.currentTimeMillis();

    Object resultObject = null;

    try {
        resultObject = pjp.proceed();
    } catch (Throwable t) {
        logFailedTransactionAndRethrow(pjp, t0, t);
    }

    logSuccessfulTransaction(pjp, t0, resultObject);

    return resultObject;
}

Answer 1

于是，我又得自己解决这个问题了。

基础知识：

1) 创建一个自定义 ServletFilter，创建 LoggableTransaction 并在那里设置令牌。我扩展了 Spring 的 OncePerRequestFilter 并使用 WebApplicationContextUtils 在 doFilterInternal 方法中获取请求范围的 bean。

2) 在web.xml 中注册此过滤器。另外一定要注册Spring的RequestContextListener和ContextLoaderListener。

3) 上面的切面实现保持不变，除了切入点引用。切入点现在引用一个服务方法（Web 服务委托给的方法）。

4）这是最关键的......如果令牌没有实现接口，那么bean定义应该用@Scope（value =“request”，proxyMode = ScopedProxyMode.TARGET_CLASS）来装饰。您将需要类路径上的 CGLib。无论如何，我需要它来实现休眠。

后来事情进展得很顺利。