主类中的 Spring-Boot @Autowired 变为 null

我想连接到 Sonic Broker 主题并侦听任何传入的 XML 消息。我做了如下的事情；

应用程序.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);
    }
 }
}

消息监听器.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());
        }
    }
 }
}

当我运行这段代码时，我在行中得到 nullPointerjmsTopicListener.listenMessage() in Application.java.

我在这里犯了什么错误？有没有办法可以改进这个（我的意思是用更少的代码完成工作）？

注意：com.mainpack 有类Application.java and ApplicationProp.javacom.msgpack.jms 有JmsTopicListener.java and MsgListner.java

来自记录器的错误：

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)

onStartup在应用程序生命周期的早期由 servlet 容器调用，并在由 servlet 容器（而不是 Spring Boot）创建的类的实例上调用。这就是为什么jmsTopicListener is null.

而不是压倒一切onStartup你可以使用带有注释的方法@PostConstruct。一旦它创建了一个实例，Spring就会调用它Application and注入任何依赖项：

@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...");
    }
}