Message Service:Send messages from one producer client to multiple consumer clients

Prerequisites

• IntelliJ IDEA is installed. For more information, see IntelliJ IDEA.

  You can use IntelliJ IDEA or Eclipse. In this example, IntelliJ IDEA is used.

• JDK 1.8 or later is installed. For more information, see Java Downloads.

• Maven 2.5 or later is installed. For more information, see Downloading Apache Maven.

Background information

MNS allows clients to consume messages in real time by pushing messages from an MNS server to clients. However, the endpoints of consumer clients are exposed to receive the message in this scenario. You cannot expose the endpoints of consumer clients in specific scenarios, such as in the private networks of an enterprise. In this case, the consumer clients can consume messages by pulling messages from the MNS server. You can combine MNS queues and topics to send messages from one client to multiple consumer clients without exposing the endpoints of the consumer clients.

Solution

Install the Java dependency library

1. Create a Java project in IntelliJ IDEA.

2. Add the following dependency to the pom.xml file to import the Java dependency library:

   <dependency>
       <groupId>com.aliyun.mns</groupId>
       <artifactId>aliyun-sdk-mns</artifactId>
       <version>1.1.9.2</version>
   </dependency>

API operations

SDK for Java 1.1.8 provides the CloudPullTopic class to support the preceding solution. You can call the following API operations provided by MNSClient to create a CloudPullTopic object:

public CloudPullTopic createPullTopic(TopicMeta topicMeta, Vector<String> queueNameList, boolean needCreateQueue, QueueMeta queueMetaTemplate)

public CloudPullTopic createPullTopic(TopicMeta topicMeta, Vector<String> queueNameList)

Sample code

package doc;

// Specify the MNS classes.
import com.aliyun.mns.client.CloudAccount;
import com.aliyun.mns.client.MNSClient;
import com.aliyun.mns.model.QueueMeta;
import com.aliyun.mns.model.TopicMeta;
import com.aliyun.mns.client.CloudPullTopic;
import com.aliyun.mns.model.TopicMessage;
import com.aliyun.mns.model.RawTopicMessage;
import com.aliyun.mns.model.Message;
import com.aliyun.mns.client.CloudQueue;
import com.aliyun.mns.common.ServiceException;
import com.aliyun.mns.common.ClientException;
import java.util.Vector;

public class DemoTopicMessageBroadcast {
    public static void main(String[] args) {
      
// Obtain the AccessKey ID and AccessKey secret of the Alibaba Cloud account and the endpoint of MNS. 
    CloudAccount account = new CloudAccount(
    ServiceSettings.getMNSAccessKeyId(),
    ServiceSettings.getMNSAccessKeySecret(),
    ServiceSettings.getMNSAccountEndpoint());
    MNSClient client = account.getMNSClient();

// Create consumers. 
Vector<String> consumerNameList = new Vector<String>();
String consumerName1 = "consumer001";
String consumerName2 = "consumer002";
String consumerName3 = "consumer003";
consumerNameList.add(consumerName1);
consumerNameList.add(consumerName2);
consumerNameList.add(consumerName3);
QueueMeta queueMetaTemplate = new QueueMeta();
queueMetaTemplate.setPollingWaitSeconds(30);

try{

    // Create a topic. 
    String topicName = "demo-topic-for-pull";
    TopicMeta topicMeta = new TopicMeta();
    topicMeta.setTopicName(topicName);
    CloudPullTopic pullTopic = client.createPullTopic(topicMeta, consumerNameList, true, queueMetaTemplate);

    // Publish a message to the topic. 
    String messageBody = "broadcast message to all the consumers:hello the world.";
    // If an original message is sent, use getMessageBodyAsRawString to parse the message body. 
    TopicMessage tMessage = new RawTopicMessage();
    tMessage.setBaseMessageBody(messageBody);
    pullTopic.publishMessage(tMessage);


    // Receive the message. 
    CloudQueue queueForConsumer1 = client.getQueueRef(consumerName1);
    CloudQueue queueForConsumer2 = client.getQueueRef(consumerName2);
    CloudQueue queueForConsumer3 = client.getQueueRef(consumerName3);

    Message consumer1Msg = queueForConsumer1.popMessage(30);
    if(consumer1Msg != null)
    {
        System.out.println("consumer1 receive message:" + consumer1Msg.getMessageBodyAsRawString());
    } else{
        System.out.println("the queue is empty");
    }

    Message consumer2Msg = queueForConsumer2.popMessage(30);
    if(consumer2Msg != null)
    {
        System.out.println("consumer2 receive message:" + consumer2Msg.getMessageBodyAsRawString());
    }else{
        System.out.println("the queue is empty");
    }

    Message consumer3Msg = queueForConsumer3.popMessage(30);
    if(consumer3Msg != null)
    {
        System.out.println("consumer3 receive message:" + consumer3Msg.getMessageBodyAsRawString());
    }else{
        System.out.println("the queue is empty");
    }

    // Delete the topic. 
    pullTopic.delete();
} catch(ClientException ce) {
    System.out.println("Something wrong with the network connection between client and MNS service."
            + "Please check your network and DNS availability.");
    ce.printStackTrace();
} catch(ServiceException se) {

    se.printStackTrace();
}

    client.close();
    }
}