java 主类中的 Spring-Boot @Autowired 为空

Spring-Boot @Autowired in main class is getting null

提问by Rajkishan Swami

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

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

Application.java

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

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

消息监听器

@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());
        }
    }
 }
}

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

当我运行此代码时，我jmsTopicListener.listenMessage()在Application.java.

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

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

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

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

Error From Logger:

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)

回答by Andy Wilkinson

onStartupis 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 jmsTopicListeneris null.

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

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

onStartup您可以使用带有注释的方法而不是覆盖@PostConstruct。一旦它创建了一个实例Application并注入了任何依赖项，它就会被 Spring 调用：

@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...");
    }
}