How to read the message in a loop in IBM MQ by using Java

Question

I wrote java class to read the message from IBM MQ queue. when i use the while loop i able to read the 1st message in the queue and I'm not able to read the 2nd message

public final void ReadMessage (String queueName) throws Exception {
    int options = MQC.MQOOINQUIRE + MQC.MQOOFAILIFQUIESCING + MQC.MQOOINPUTSHARED;
    System.out.printin ("start Creating the Queue.")
    MQQueue myQueue = this.mqManager.accessQueue(queueName, options) ;

    MQMessage mgMessage = new MQMessage ( ) ;
    MQGetMessageOptions gmo = new MQGetMessageOptions ( ) ;
    gmo.options = MQC.MQGMO NO WAIT + MQC.MQGMO FAIL IF QUIESCING;
    gmo.matchOptions = MQC.MQMO NONE;
    gmo.waitlnterval = 15000;
    boolean msgqueue=true;
    while(msgqueue){
        try {
            System.out.println("end of get Message from myqueue");
            System.out.println("Message length" + mgMessage());
            mgMessage.characterSet = 300;
            int length = mqMessage.getMessageLength( );

            System.out.println("The message" + length);
            System.out.println("The message" + mgMessage.readString(length));
            gmo.options = MQC.MQGMOWAIT | MQC.MQGMOBROWSENEXT;

            if(mgMessage.getCurrentDepth()==1){
                msgqueue=false;
            }
        }
        catch (Exception e) {
            msgqueue=false;
        }
    }
}

I would like know what else i need to add in order to move next message in the queue.

Thanks

Answer 1

if(mgMessage.getCurrentDepth()==1)

It is bad practice to perform MQGets based on the current depth. The current depth will include uncommitted messages in a transaction!!

Here is a fully functioning Java program that will get messages in a loop from 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.MQMessage;
import com.ibm.mq.MQGetMessageOptions;
import com.ibm.mq.MQQueue;
import com.ibm.mq.MQQueueManager;
import com.ibm.mq.constants.CMQC;

/**
 * Program Name
 *  MQTest12L
 *
 * Description
 *  This java class will connect to a remote queue manager with the 
 *  MQ setting stored in a HashTable, loop to retrieve all messages on a queue
 *  then close and disconnect.
 *
 * 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 MQTest12L
{
   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;
   private String qMgrName;
   private String outputQName;

   /**
    * The constructor
    */
   public MQTest12L()
   {
      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())
      {
         qMgrName = (String) params.get("-m");
         outputQName = (String) params.get("-q");

         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();
      }
   }

   /**
    * Connect, open queue, loop and get all messages then close queue and disconnect.
    *
    */
   private void testReceive()
   {
      MQQueueManager qMgr = null;
      MQQueue queue = null;
      int openOptions = CMQC.MQOO_INPUT_AS_Q_DEF + CMQC.MQOO_INQUIRE + CMQC.MQOO_FAIL_IF_QUIESCING;
      MQGetMessageOptions gmo = new MQGetMessageOptions();
      gmo.options = CMQC.MQGMO_NO_WAIT + CMQC.MQGMO_FAIL_IF_QUIESCING;
      MQMessage receiveMsg = null;
      int msgCount = 0;
      boolean getMore = true;

      try
      {
         qMgr = new MQQueueManager(qMgrName, mqht);
         MQTest12L.logger("successfully connected to "+ qMgrName);

         queue = qMgr.accessQueue(outputQName, openOptions);
         MQTest12L.logger("successfully opened "+ outputQName);

         while(getMore)
         {
            receiveMsg = new MQMessage();

            try
            {
               // get the message on the queue
               queue.get(receiveMsg, gmo);
               msgCount++;

               if (CMQC.MQFMT_STRING.equals(receiveMsg.format))
               {
                  String msgStr = receiveMsg.readStringOfByteLength(receiveMsg.getMessageLength());
//                  MQTest12L.logger("["+msgCount+"] " + msgStr);
               }
               else
               {
                  byte[] b = new byte[receiveMsg.getMessageLength()];
                  receiveMsg.readFully(b);
//                  MQTest12L.logger("["+msgCount+"] " + new String(b));
               }
            }
            catch (MQException e)
            {
               if ( (e.completionCode == CMQC.MQCC_FAILED) && 
                    (e.reasonCode == CMQC.MQRC_NO_MSG_AVAILABLE) )
               {
                  // All messages read.
                  getMore = false;
                  break;
               }
               else
               {
                  MQTest12L.logger("MQException: " + e.getLocalizedMessage());
                  MQTest12L.logger("CC=" + e.completionCode + " : RC=" + e.reasonCode);
                  getMore = false;
                  break;
               }
            }
            catch (IOException e)
            {
               MQTest12L.logger("IOException:" +e.getLocalizedMessage());
            }
         }
      }
      catch (MQException e)
      {
         MQTest12L.logger("CC=" +e.completionCode + " : RC=" + e.reasonCode);
      }
      finally
      {
         MQTest12L.logger("read " + msgCount + " messages");

         try
         {
            if (queue != null)
            {
               queue.close();
               MQTest12L.logger("closed: "+ outputQName);
            }
         }
         catch (MQException e)
         {
            MQTest12L.logger("CC=" +e.completionCode + " : RC=" + e.reasonCode);
         }
         try
         {
            if (qMgr != null)
            {
               qMgr.disconnect();
               MQTest12L.logger("disconnected from "+ qMgrName);
            }
         }
         catch (MQException e)
         {
            MQTest12L.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);
   }

   /**
    * main line
    * @param args
    */
   public static void main(String[] args)
   {
      MQTest12L write = new MQTest12L();

      try
      {
         write.init(args);
         write.testReceive();
      }
      catch (IllegalArgumentException e)
      {
         System.err.println("Usage: java MQTest12L -m QueueManagerName -h host -p port -c channel -q QueueName -u UserID -x Password");
         System.exit(1);
      }

      System.exit(0);
   }
}

Answer 2

If you do not move the MQMessage constructor in the loop, like @Shashi recommended, you have to do the following in the loop:

mgMessage.clearMessage();
mgMessage.correlationId = MQC.MQCI_NONE;
mgMessage.messageId = MQC.MQMI_NONE;

Answer 3

I would try by moving the two lines inside the while loop because queue.get() call updates MQMessage object instance when it returns.

   MQMessage mgMessage = new MQMessage ( ) ; 
   MQGetMessageOptions gmo = new MQGetMessageOptions ( ) ; 

Since the same MQMessage object is passed for the next call, the get call uses the updated MQMessage object and tries get message a message which has already been got.