主类中的Spring-Boot @Autowired变为空

问题描述：

我想连接到Sonic Broker主题并侦听任何传入的XML消息.我做了下面的事情；

I want to connect to a Sonic Broker Topic and Listen for any incoming XML message. I did something like below;

Application.java

@SpringBootApplication
@ComponentScan({"com.mainpack", "com.msgpack.jms"})
@EnableJms
public class Application extends SpringBootServletInitializer {

@Autowired
private JmsTopicListener jmsTopicListener;

@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
    return application.sources(Application.class);
}

@Override
public void onStartup(final ServletContext servletContext) throws ServletException {
    try {
        LogService.info(Application.class.getName(), "Starting Service...");
        super.onStartup(servletContext);
        jmsTopicListener.listenMessage();
        LogService.info(Application.class.getName(), "Service Started");
    } catch (Exception ex) {
        LogService.error(this.getClass().getName(), ex);
    }
}

public static void main(String[] args) {
    ApplicationContext context = SpringApplication.run(Application.class, args);
    LogService.info(Application.class.getName(), "Service Started...");
 }
}

JmsTopicListener.java

@Component
public class JmsTopicListener {

@Autowired
private ApplicationProperties properties;

@Autowired
private MsgListener msgListener;

public void listenMessage() {
    TopicConnectionFactory factory;
    TopicConnection connection = null;
    LogService.info(this.getClass().getName(), "Registering Broker Connection");
    try {
        factory = new progress.message.jclient.TopicConnectionFactory(properties.getBrokerURL());
        connection = factory.createTopicConnection(properties.getUserName(), properties.getPass());

        javax.jms.TopicSession subSession = (TopicSession) connection.createTopicSession(false, Session.AUTO_ACKNOWLEDGE);

        javax.jms.Topic topic = subSession.createTopic(properties.getTopicName());
        MessageConsumer subscriber = subSession.createSubscriber(topic);
        subscriber.setMessageListener(msgListener);
        connection.start();
        LogService.info(this.getClass().getName(), "Broker connected");
    } catch (Exception ex) {
        LogService.error(this.getClass().getName(), ex);
    }
 }
}

MsgListener.java

@Component
public class MsgListener implements MessageListener {

@Override
public void onMessage(Message msg) {
    if (msg instanceof XMLMessage) {
        try {
            XMLMessage m = (XMLMessage) msg;
            if (m.getText().contains("Applications")) {
                LogService.info(this.getClass().getName(), "Recieved A Applications Message");
            } else {
                LogService.info(this.getClass().getName(), "Recieved Message Does not contain Applications Tag");
            }
        } catch (Exception ex) {
            LogService.info(this.getClass().getName(), "Exception: " + ex.getMessage());
        }
    }
 }
}

当我运行此代码时，在 Application.java 中的 jmsTopicListener.listenMessage()行中获得nullPointer.

When, i run this code i get nullPointer at line jmsTopicListener.listenMessage() in Application.java.

我在这里犯了什么错误?有什么办法可以改善这一点(我的意思是可以用更少的代码完成工作)?.

What mistake i have made here? Is there a way i can improve this (I mean get the work done in less code maybe)?.

注意:com.mainpack具有类 Application.java 和 ApplicationProp.java com.msgpack.jms具有 JmsTopicListener.java 和 MsgListner.java

NOTE: com.mainpack have classes Application.java and ApplicationProp.java com.msgpack.jms have JmsTopicListener.java and MsgListner.java

记录器错误:

ERROR [2015-07-14 14:34:52] [com.mainpack.Application] [localhost-startStop-1] - [Exception: ]java.lang.NullPointerException
    at com.mainpack.Application.onStartup(Application.java:33)
    at org.springframework.web.SpringServletContainerInitializer.onStartup(SpringServletContainerInitializer.java:175)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5156)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:725)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:701)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:717)
    at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:945)
    at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1768)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

servlet容器在应用程序生命周期的早期就调用了

答

onStartup ，并在由创建的类的实例上调用了servlet容器，而不是Spring Boot.这就是为什么 jmsTopicListener 为 null 的原因.

onStartup is called by the servlet container very early in your application's lifecycle and is called on an instance of the class that was created by the servlet container, not Spring Boot. This is why jmsTopicListener is null.

您可以使用带有 @PostConstruct 注释的方法，而不是覆盖 onStartup .一旦创建了 Application 的实例并注入了任何依赖项，Spring就会调用它:

Rather than overriding onStartup you could use a method annotated with @PostConstruct. It will be called by Spring once it's created an instance of Application and injected any dependencies:

@SpringBootApplication
@ComponentScan({"com.mainpack", "com.msgpack.jms"})
@EnableJms
public class Application extends SpringBootServletInitializer {

    @Autowired
    private JmsTopicListener jmsTopicListener;

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(Application.class);
    }

    @PostConstruct
    public void listen() { 
        jmsTopicListener.listenMessage();
    }

    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(Application.class, args);
        LogService.info(Application.class.getName(), "Service Started...");
    }
}

主类中的Spring-Boot @Autowired变为空

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