java - 为什么连接 JMS 服务的 java 代码无法编译？

Question

我一直在使用 GlassFish 服务器来处理项目，以使用我的 java 代码连接 JMS 服务。 我已经创建了connectionFactory、队列和主题，如下所述。

1. jms/GlassFishBookConnectionFactory connectionfactory
2. jms/GlassFishBookQueue queue
3. jms/GlassFishBookTopic

这是我的 java 代码，用于连接到上述连接的 JMS 服务。我一直按照给定网址的步骤进行处理。 http://www.packtpub.com/article/setting-glassfish-jms-and-working-message-queues 我刚刚开始研究JMS服务。我在这方面的工作并不完美。我已经下载了 java.jms jar 文件并将其解压。

package net.ensode.glassfishbook;

import javax.annotation.Resource;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.JMSException;
import javax.jms.MessageProducer;
import javax.jms.Queue;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.jms.*;

public class MessageSender
{
  @Resource(mappedName = "jms/GlassFishBookConnectionFactory")
  private static ConnectionFactory connectionFactory;
  @Resource(mappedName = "jms/GlassFishBookQueue")
  private static Queue queue;

  public void produceMessages()
  {
    MessageProducer messageProducer;
    TextMessage textMessage;
    try
    {
      Connection connection = connectionFactory.createConnection();
      Session session = connection.createSession(false,
        Session.AUTO_ACKNOWLEDGE);
      messageProducer = session.createProducer(queue);
      textMessage = session.createTextMessage();

      textMessage.setText("Testing, 1, 2, 3. Can you hear me?");
      System.out.println("Sending the following message: "
        + textMessage.getText());
      messageProducer.send(textMessage);

      textMessage.setText("Do you copy?");
      System.out.println("Sending the following message: "
        + textMessage.getText());
      messageProducer.send(textMessage);

      textMessage.setText("Good bye!");
      System.out.println("Sending the following message: "
        + textMessage.getText());
      messageProducer.send(textMessage);

      messageProducer.close();
      session.close();
      connection.close();
    }
    catch (JMSException e)
    {
      e.printStackTrace();
    }
  }
  public static void main(String[] args)
  {
    new MessageSender().produceMessages();
  }
}

当前当我编译此代码时。我收到类似

的错误

Exception in thread "main" java.lang.NullPointerException
    at net.ensode.glassfishbook.MessageSender.produceMessages(MessageSender.java:26)
    at net.ensode.glassfishbook.MessageSender.main(MessageSender.java:58)

Answer 1

显然，资源没有被注入(inject)到您的类中，因为您将其作为独立应用程序运行。

引用您链接的文章:

Before delving into the details of this code, alert readers might have noticed that this class is a standalone Java application as it contains a main method. As this class is standalone, it executes outside the application server. In spite of this, we can see that some resources are injected into it, specifically the connection factory and queue. The reason we can inject resources into this code, even though it runs outside the application server, is because GlassFish includes a utility called appclient.

This utility allows us to "wrap" an executable JAR file and allows it to have access to the application server resources. To execute the previous code, assuming it is packaged in an executable JAR file called jmsptpproducer.jar, we would type the following command in the command line:

appclient -client jmsptpproducer.jar

尝试按上述方式运行应用程序。