如何在两个 servlet 之间通过 apacheMQ 发送消息？

Question

我正在尝试将 apacheMQ 集成到我在 Tomcat 上运行的 Web 应用程序中。我找到了一些关于本地集成的教程（我不打算进行全局集成），但我不确定如何进行。对于初学者来说，所有的教程似乎都很混乱。

能否请您看一下我的代码并建议我是否在正确的道路上实现它？我的意图是从一个 servlet 发送一些消息（将其添加到队列中），然后从具有不同 servlet 的队列中读取这些消息。

此代码基于THIS TUTORIAL。

消息处理类：

public class Messenger {

    public static void sendMessage(String msg) {
        // configure the broker
        try {
            // Create a ConnectionFactory
            ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
                    "vm://localhost");

            // Create a Connection
            Connection connection = connectionFactory.createConnection();
            connection.start();

            // Create a Session
            Session session = connection.createSession(false,
                    Session.AUTO_ACKNOWLEDGE);

            // Create the destination (Topic or Queue)
            Destination destination = session.createQueue("TEST.FOO");

            // Create a MessageProducer from the Session to the Topic or Queue
            MessageProducer producer = session.createProducer(destination);
            producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

            // Create a messages
            TextMessage message = session.createTextMessage(msg);

            // Tell the producer to send the message
            System.out.println("Sent message: " + message.getText());
            producer.send(message);

            // Clean up
            session.close();
            connection.close();

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public static void readQueue() {
        try {

            // Create a ConnectionFactory
            ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
                    "vm://localhost");

            // Create a Connection
            Connection connection = connectionFactory.createConnection();
            connection.start();

            // Create a Session
            Session session = connection.createSession(false,
                    Session.AUTO_ACKNOWLEDGE);

            // Create the destination (Topic or Queue)
            Destination destination = session.createQueue("TEST.FOO");

            // Create a MessageConsumer from the Session to the Topic or Queue
            MessageConsumer consumer = session.createConsumer(destination);

            // Wait for a message
            Message message = consumer.receive(1000);

            if (message instanceof TextMessage) {
                TextMessage textMessage = (TextMessage) message;
                String text = textMessage.getText();
                System.out.println("Received: " + text);
            } else {
                System.out.println("Received: " + message);
            }

            consumer.close();
            session.close();
            connection.close();
        } catch (Exception e) {
            System.out.println("Caught: " + e);
            e.printStackTrace();
        }
    }

}

目前，我在控制台中打印所有内容就足够了，因为此示例仅用于测试和调试目的。

发送和接收 servlet：

public class SendMessageServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");

        Messenger.sendMessage("Test message");


    }

}

public class ReadQueueServlet extends HttpServlet {

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html");

        Messenger.readQueue();

    }

}

访问ReadQueueServlet的结果只是“Received: null”。

我不确定在这种情况下是否应该为我的 Web 应用程序创建 context.xml，但我也尝试过。我将以下内容放在WEB-INF/META-INF/context.xml：

<?xml version="1.0" encoding="UTF-8"?>
<Context>
    <Resource auth="Container"
          name="jms/ConnectionFactory"
          type="org.apache.activemq.ActiveMQConnectionFactory"
          description="JMS Connection Factory"
          factory="org.apache.activemq.jndi.JNDIReferenceFactory"
          brokerURL="vm://localhost?brokerConfig=xbean:activemq.xml"
          brokerName="MyActiveMQBroker"/>

<Resource auth="Container"
          name="jms/FooQueue"
          type="org.apache.activemq.command.ActiveMQQueue"
          description="JMS queue"
          factory="org.apache.activemq.jndi.JNDIReferenceFactory"
          physicalName="FOO.QUEUE"/>
</Context>

感谢任何帮助。

Answer 1

访问ReadQueueServlet的结果只是“Received: null”。

这是因为队列中没有消息。

        // Wait for a message
        Message message = consumer.receive(1000);

        if (message instanceof TextMessage) {
            TextMessage textMessage = (TextMessage) message;
            String text = textMessage.getText();
            System.out.println("Received: " + text);
        } else {
            System.out.println("Received: " + message);
        }

如果看到documentation的接收方法

返回： 为该消息消费者生成的下一条消息，如果超时或该消息消费者同时关闭，则返回 null

因此，在时间到期后，您将获得 null。您的代码进入 else 块并打印为 null 的消息。