consume all messages from IBM MQ

Question

I want to consume all messages from MQ.

public static void main(String[] args)
{ 
 JMSContext context = null;
 Destination destination = null;
 JMSConsumer consumer = null;

 JmsFactoryFactory FF = JmsFactoryFactory.getInstance(WMQConstants.WMQ_PROVIDER);
 JmsConnectionFactor CF = FF.createConnectionFactory();
  context = CF.createContext();
  destination = context.createQueue(QUEUE_NAME);
  consumer = context.createConsumer(destination);
  String msg = consumer.receiveBody(String.class, 15090);
  System.out.println(msg);
 }

It is able to read one message only. How can I consume all messages? Also, is there any simpler way to delete all messages in queue without even reading or consuming them?

Answer 1

The JMS API consumes a single message at a time so you'll need to put your receiveBody in a loop, eg:

public static void main(String[] args) { 
   JMSContext context = null;
   Destination destination = null;
   JMSConsumer consumer = null;

   JmsFactoryFactory FF = JmsFactoryFactory.getInstance(WMQConstants.WMQ_PROVIDER);
   JmsConnectionFactor CF = FF.createConnectionFactory();
   context = CF.createContext();
   destination = context.createQueue(QUEUE_NAME);
   consumer = context.createConsumer(destination);
   String msg = null;
   do {
      msg = consumer.receiveBody(String.class, 15090);
      System.out.println(msg);
   } while (msg != null);
}

When receiveBody returns null that means there's no more messages in the queue.

The JMS API doesn't define any way to delete all the messages from a queue, but most JMS servers have an implementation-specific management API through which you can perform those sorts of actions.

Answer 2

If, as your question suggests, all you want to do is empty a queue of all its messages and not actually read them in an application, you could consider simply using the administrative MQSC command:-

CLEAR QLOCAL(queue-name)

You can type this into the runmqsc tool to issue it to the queue manager.

Answer 3

is there any simpler way to delete all messages in queue without even reading or consuming them?

Yes. You can use the MQ PCF Clear Queue command, so long as no application has the queue open for input or output. ie IPPROCS and OPPROCS must be zero for it to work. This is also true for Morag's MQSC Clear command.

Here is a fully functioning Java MQ PCF program to clear a queue.

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Hashtable;

import com.ibm.mq.MQException;
import com.ibm.mq.MQQueueManager;
import com.ibm.mq.constants.CMQC;
import com.ibm.mq.constants.CMQCFC;
import com.ibm.mq.headers.MQDataException;
import com.ibm.mq.headers.pcf.PCFMessage;
import com.ibm.mq.headers.pcf.PCFMessageAgent;

/**
 * Program Name
 *  MQClearQueue01
 *
 * Description
 *  This java class issues a PCF "Clear Q" command for a queue to delete all messages 
 *  in the queue of a remote queue manager.
 *
 * Sample Command Line Parameters
 *  -m MQA1 -h 127.0.0.1 -p 1414 -c TEST.CHL -q TEST.Q1 -u UserID -x Password
 *
 * @author Roger Lacroix
 */
public class MQClearQueue01
{
   private static final SimpleDateFormat  LOGGER_TIMESTAMP = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS");

   private Hashtable<String,String> params;
   private Hashtable<String,Object> mqht;

   public MQClearQueue01()
   {
      super();
      params = new Hashtable<String,String>();
      mqht = new Hashtable<String,Object>();
   }

   /**
    * Make sure the required parameters are present.
    * @return true/false
    */
   private boolean allParamsPresent()
   {
      boolean b = params.containsKey("-h") && params.containsKey("-p") &&
                  params.containsKey("-c") && params.containsKey("-m") &&
                  params.containsKey("-q") &&
                  params.containsKey("-u") && params.containsKey("-x");
      if (b)
      {
         try
         {
            Integer.parseInt((String) params.get("-p"));
         }
         catch (NumberFormatException e)
         {
            b = false;
         }
      }

      return b;
   }

   /**
    * Extract the command-line parameters and initialize the MQ HashTable.
    * @param args
    * @throws IllegalArgumentException
    */
   private void init(String[] args) throws IllegalArgumentException
   {
      int port = 1414;
      if (args.length > 0 && (args.length % 2) == 0)
      {
         for (int i = 0; i < args.length; i += 2)
         {
            params.put(args[i], args[i + 1]);
         }
      }
      else
      {
         throw new IllegalArgumentException();
      }

      if (allParamsPresent())
      {
         try
         {
            port = Integer.parseInt((String) params.get("-p"));
         }
         catch (NumberFormatException e)
         {
            port = 1414;
         }

         mqht.put(CMQC.CHANNEL_PROPERTY, params.get("-c"));
         mqht.put(CMQC.HOST_NAME_PROPERTY, params.get("-h"));
         mqht.put(CMQC.PORT_PROPERTY, new Integer(port));
         mqht.put(CMQC.USER_ID_PROPERTY, params.get("-u"));
         mqht.put(CMQC.PASSWORD_PROPERTY, params.get("-x"));

         // I don't want to see MQ exceptions at the console.
         MQException.log = null;
      }
      else
      {
         throw new IllegalArgumentException();
      }
   }

   /**
    * Handle connecting to the queue manager, issuing PCF command then
    * looping through PCF response messages and disconnecting from
    * the queue manager.
    */
   private void doPCF()
   {
      MQQueueManager  qMgr   = null;
      PCFMessageAgent agent  = null;
      PCFMessage   request   = null;
      PCFMessage[] responses = null;
      String qMgrName  = (String) params.get("-m");
      String queueName = (String) params.get("-q");

      try
      {
         qMgr = new MQQueueManager(qMgrName, mqht);
         MQClearQueue01.logger("successfully connected to "+ qMgrName);

         agent = new PCFMessageAgent(qMgr);
         MQClearQueue01.logger("successfully created agent");

         // https://www.ibm.com/support/knowledgecenter/SSFKSJ_latest/com.ibm.mq.ref.adm.doc/q087420_.html
         request = new PCFMessage(CMQCFC.MQCMD_CLEAR_Q);

         request.addParameter(CMQC.MQCA_Q_NAME, queueName);

         responses = agent.send(request);

         MQClearQueue01.logger("responses.length="+responses.length);

         for (int i = 0; i < responses.length; i++)
         {
            if ((responses[i]).getCompCode() == CMQC.MQCC_OK)
               MQClearQueue01.logger("Successfully cleared queue '"+queueName+"' of messages.");
            else
               MQClearQueue01.logger("Error: Failed to clear queue '"+queueName+"' of messages.");
         }
      }
      catch (MQException e)
      {
         MQClearQueue01.logger("CC=" +e.completionCode + " : RC=" + e.reasonCode);
      }
      catch (IOException e)
      {
         MQClearQueue01.logger("IOException:" +e.getLocalizedMessage());
      }
      catch (MQDataException e)
      {
         MQClearQueue01.logger("MQDataException:" +e.getLocalizedMessage());
      }
      finally
      {
         try
         {
            if (agent != null)
            {
               agent.disconnect();
               MQClearQueue01.logger("disconnected from agent");
            }
         }
         catch (MQDataException e)
         {
            MQClearQueue01.logger("CC=" +e.completionCode + " : RC=" + e.reasonCode);
         }

         try
         {
            if (qMgr != null)
            {
               qMgr.disconnect();
               MQClearQueue01.logger("disconnected from "+ qMgrName);
            }
         }
         catch (MQException e)
         {
            MQClearQueue01.logger("CC=" +e.completionCode + " : RC=" + e.reasonCode);
         }
      }
   }

   /**
    * A simple logger method
    * @param data
    */
   public static void logger(String data)
   {
      String className = Thread.currentThread().getStackTrace()[2].getClassName();

      // Remove the package info.
      if ( (className != null) && (className.lastIndexOf('.') != -1) )
         className = className.substring(className.lastIndexOf('.')+1);

      System.out.println(LOGGER_TIMESTAMP.format(new Date())+" "+className+": "+Thread.currentThread().getStackTrace()[2].getMethodName()+": "+data);
   }

   public static void main(String[] args)
   {
      MQClearQueue01 mqcq = new MQClearQueue01();

      try
      {
         mqcq.init(args);
         mqcq.doPCF();
      }
      catch (IllegalArgumentException e)
      {
         MQClearQueue01.logger("Usage: java MQClearQueue01 -m QueueManagerName -h host -p port -c channel -q QueueName -u UserID -x Password");
         System.exit(1);
      }

      System.exit(0);
   }
}