Read multiple messages at a time from IBM MQ in java

Question

I have a below code snippet which reads a message from IBM MQ. The message is getting retrieved and also the current depth.

import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.Queue;
import javax.jms.QueueReceiver;
import javax.jms.Session;
import javax.jms.TextMessage;

import com.ibm.mq.MQC;
import com.ibm.mq.MQEnvironment;
import com.ibm.mq.MQGetMessageOptions;
import com.ibm.mq.MQMessage;
import com.ibm.mq.MQPutMessageOptions;
import com.ibm.mq.MQQueueManager;
import com.ibm.mq.jms.JMSC;
import com.ibm.mq.jms.MQQueue;
import com.ibm.mq.jms.MQQueueConnection;
import com.ibm.mq.jms.MQQueueConnectionFactory;
import com.ibm.mq.jms.MQQueueReceiver;
import com.ibm.mq.jms.MQQueueSession;

public class HelloConsumer {

    /**
     * @param args
     */
    
    public HelloConsumer(){
        
        try {
            
            com.ibm.mq.MQQueue defaultLocalQueue;
            MQQueueManager qManager=null;
            
            MQEnvironment.hostname = "ctmq005";
            MQEnvironment.channel = "CLIENTCONNECTION";
            MQEnvironment.port = 1414;
            String qMngrStr = "";
            qManager = new MQQueueManager(qMngrStr); 
            int openOptions = MQC.MQOO_INPUT_AS_Q_DEF | MQC.MQOO_OUTPUT | MQC.MQOO_INQUIRE | MQC.MQ_Q_NAME_LENGTH; 
            String queueName="test.q01";
            System.out.println("accessing::"+queueName);
            defaultLocalQueue = qManager.accessQueue(queueName, openOptions);
            //set transport properties.
            System.out.println("set MQ props");
            MQEnvironment.properties.put(MQC.TRANSPORT_PROPERTY, MQC.TRANSPORT_MQSERIES_CLIENT);
            System.out.println("new Queuemanager");
            //MQMessage putMessage = new MQMessage();
            //String msg = "hello";
           // putMessage.writeUTF(msg);
            
            //specify the message options...
            MQPutMessageOptions pmo = new MQPutMessageOptions(); 
            // accept 
            // put the message on the queue
            //defaultLocalQueue.put(putMessage, pmo);
              
            MQMessage getMessages = new MQMessage();
            MQGetMessageOptions gmo = new MQGetMessageOptions();
            System.out.println("get messages::"+gmo.toString());
            defaultLocalQueue.get(getMessages, gmo);
            int depth = defaultLocalQueue.getCurrentDepth();
            byte[] b = new byte[getMessages.getMessageLength()]; 
            System.out.println(depth);
            getMessages.readUTF();
            System.out.println("Message got from MQ: "+new String(b));
        }
        catch(Exception jex){
            jex.printStackTrace();
        }
    }

    public static void main(String[] args) {
        
        new HelloConsumer();

    }

This code reads only one message at a time from the Queue. I want to read multiple messages at a time from the Queue. For example, if there are 4 messages in the queue , I want to read all of them and so some processing for each message(processing code not attached here). Please suggest how to achieve this.

No, it is not possible to read multiple messages with one get call. You will always get (read) one message at a time. — Shashi
You would need to do multiple gets as @Shashi mentioned. What is the usecase you are trying to solve? If they were non-persistent then MQ does have a read ahead feature but this still requires you to issue multiple gets and probably is not implemented in IBM MQ classes for Java, only JMS. — JoshMc

Roger Roger · Accepted Answer · 2020-08-11T16:38:32

Why don't you create a simply method i.e. getAllMessages to do it for you and have it return an ArrayList of MQMessage class.

/**
 * Retrieve the messages as an array
 * @return msgs
 */
public ArrayList<MQMessage> getAllMessages(MQQueue inQ)
{
   private ArrayList<MQMessage> msgs = new ArrayList<MQMessage>();
   MQGetMessageOptions gmo = new MQGetMessageOptions();
   gmo.options = CMQC.MQGMO_NO_WAIT + CMQC.MQGMO_FAIL_IF_QUIESCING;

   MQMessage getMsg = null;
   boolean getMore = true;

   while(getMore)
   {
      try
      {
         getMsg = new MQMessage();
         inQ.get(getMsg, gmo);
         msgs.add(getMsg);
      }
      catch (MQException e)
      {
         if ( (e.completionCode == CMQC.MQCC_FAILED) &&
              (e.reasonCode == CMQC.MQRC_NO_MSG_AVAILABLE) )
         {
            getMore = false;
            break;
         }
         else
         {
            System.out.println("GET Exception: "+e.getMessage());
            System.out.println("getCause()="+e.getCause());
            getMore = false;
            break;
         }
      }

   }

   return msgs;
}

Read multiple messages at a time from IBM MQ in java

1 Answers