Autowired 为 bean 提供 null答案

【问题标题】：Autowired gives null for the beanAutowired 为 bean 提供 null
【发布时间】：2017-05-02 09:36:01
【问题描述】：

我正在使用带有 Spring Boot 的 Axon 框架。在我的事件处理程序中自动装配类时遇到问题。在事件处理程序中自动装配的 bean 之一始终为空。我的事件处理程序类看起来像这样 -

@Component
public class CustomerAddedEventHandler {

    @Autowired
    QueueMessageProducer queueMessageProducer;

    @EventHandler
    public void handle(CustomerAddedEvent event) {

        System.out.println("Got event in handler");

        queueMessageProducer.writeMessage(event.toString());
    }
}

而QueueMessageProducer类如下-

@Component
public class QueueMessageProducer {

    private static final Logger LOG = LoggerFactory.getLogger(QueueMessageProducer.class);

    @Autowired
    private JmsMessagingTemplate jmsMessagingTemplate;

    @Autowired
    private Queue queue;

    public void writeMessage(String message) {

        send(message);
    }

    private void send(String msg) {

        LOG.debug("Writing message on queue with name - " + "sTests" + " - " + msg);

        jmsMessagingTemplate.convertAndSend(queue, msg);
    }
}

主类-

@SpringBootApplication
@EnableJms
public class SimpleEventStoreMessageProducerApplication {

    public static void main(String[] args) {
        SpringApplication.run(SimpleEventStoreMessageProducerApplication.class, args);
    }

    @Bean
    public EventStore eventStore() {

        return new FileSystemEventStore(new SimpleEventFileResolver(new File("./events")));
    }

    @Bean
    public Queue queue() {
        return new ActiveMQQueue("sTest");
    }

    @Bean
    public AggregateAnnotationCommandHandler<CustomerAggregate> aggregateAnnotationCommandHandler() {

        Repository<CustomerAggregate> repository = new EventSourcingRepository<>(CustomerAggregate.class, eventStore());

        return new AggregateAnnotationCommandHandler<>(CustomerAggregate.class, repository);
    }
}

但在 CustomerAddEventHandler 类中 QueueMessageProducer 始终为空。请帮忙。

更新

stacktrace如下-

2017-05-02 15:26:51.911 ERROR 4168 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.NullPointerException] with root cause

java.lang.NullPointerException: null
    at com.poc.handlers.CustomerAddedEventHandler.handle(CustomerAddedEventHandler.java:21) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_25]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_25]
    at org.axonframework.common.annotation.MethodMessageHandler.invoke(MethodMessageHandler.java:85) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.common.annotation.MessageHandlerInvoker.invokeHandlerMethod(MessageHandlerInvoker.java:67) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.eventhandling.annotation.AnnotationEventListenerAdapter.handle(AnnotationEventListenerAdapter.java:120) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.eventhandling.SimpleEventBus.publish(SimpleEventBus.java:90) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.unitofwork.DefaultUnitOfWork.publishEvents(DefaultUnitOfWork.java:270) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.unitofwork.DefaultUnitOfWork.doCommit(DefaultUnitOfWork.java:140) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.unitofwork.NestableUnitOfWork.commit(NestableUnitOfWork.java:59) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.SimpleCommandBus.doDispatch(SimpleCommandBus.java:137) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.SimpleCommandBus.doDispatch(SimpleCommandBus.java:103) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.SimpleCommandBus.dispatch(SimpleCommandBus.java:75) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.gateway.AbstractCommandGateway.send(AbstractCommandGateway.java:81) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.gateway.DefaultCommandGateway.send(DefaultCommandGateway.java:86) ~[axon-core-2.4.3.jar:2.4.3]
    at org.axonframework.commandhandling.gateway.DefaultCommandGateway.sendAndWait(DefaultCommandGateway.java:104) ~[axon-core-2.4.3.jar:2.4.3]
    at com.poc.processor.CommandGenerator.sendCommands(CommandGenerator.java:16) ~[classes/:na]
    at com.poc.processor.CommandRouter.runTest(CommandRouter.java:41) ~[classes/:na]
    at com.poc.controller.SimpleCommandBusController.runTest(SimpleCommandBusController.java:19) ~[classes/:na]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_25]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_25]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_25]
    at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_25]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:221) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:136) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:114) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:963) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) ~[tomcat-embed-websocket-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:89) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:77) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.3.RELEASE.jar:4.3.3.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) ~[tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:108) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:784) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:802) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1410) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_25]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_25]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.5.jar:8.5.5]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_25]

【问题讨论】：

QueueMessageProducer 和 SimpleEventStoreMessageProducerApplication 是在两个不同的包还是同一个包？
它们在不同的包中
显示异常消息的完整堆栈跟踪。 QueueMessageProducer 类中的自动装配 bean 可能存在问题
当然，我正在更新问题

标签： java spring-boot activemq axon

【解决方案1】：

我认为您需要在 SimpleEventStoreMessageProducerApplication 类中添加 ComponentScan 或 scanBasePackages

要么

@SpringBootApplication(scanBasePackages = { "com.example" })

或

@SpringBootApplication
@ComponentScan("com.example")

你可以用你的包替换“com.example”。

【讨论】：

【解决方案2】：

可能是 QueueMessageProducer 被加载后的事件处理程序。您可以在事件处理程序中为自动装配的 QueueMessageProducer 尝试 @Lazy 注释吗？

【讨论】：