How to send JMS message over MQ in .NET?

1
votes

I'm working on something which could be described as custom WMQ message router/forwarder. At the moment I have some very confusing issue with processing JMS messages send over MQ. I'm able to receive message send from Java application over JMS (with MQ as transport) but I'm not able to send message to Java application listening on JMS endpoint.

I have a testing servlet and message driven bean - both hosted in WebSphere Application Server 7.0 (with WebSphere MQ 7.0 used for message transport). Servlet is able to communicate with the bean but if I put my forwarder between them (by reconfiguring the servlet to communicate with forwarder which will reconstruct messages and forward them to bean) the bean is not able to process the request. I have this error in WAS log:

[8/2/12 14:38:51:359 CEST] 00000031 SibMessage    W   [:] CWSJY0003W: JMSCC0110: An exception '
                       Message : java.lang.NullPointerException
                         Class : class java.lang.NullPointerException
                         Stack : com.ibm.msg.client.wmq.internal.messages.WMQMessageBase._parseMcdFolder(WMQMessageBase.java:445)
                               : com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.constructProviderMessageFromRFH2(WMQReceiveMarshal.java:341)
                               : com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.createProviderMessage(WMQReceiveMarshal.java:447)
                               : com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.exportProviderMessage(WMQReceiveMarshal.java:607)
                               : com.ibm.msg.client.wmq.internal.WMQConsumerShadow.getMsg(WMQConsumerShadow.java:1115)
                               : com.ibm.msg.client.wmq.internal.WMQSyncConsumerShadow.receive(WMQSyncConsumerShadow.java:334)
                               : com.ibm.msg.client.wmq.internal.WMQSession.loadMessageReference(WMQSession.java:1082)
                               : com.ibm.msg.client.jms.internal.JmsSessionImpl.consume(JmsSessionImpl.java:2847)
                               : com.ibm.msg.client.jms.internal.JmsSessionImpl.run(JmsSessionImpl.java:2549)
                               : com.ibm.mq.jms.MQSession.run(MQSession.java:860)
                               : com.ibm.mq.connector.inbound.WorkImpl.run(WorkImpl.java:172)
                               : com.ibm.ejs.j2c.work.WorkProxy.run(WorkProxy.java:399)
                               : com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1604)
[8/2/12 14:38:51:781 CEST] 00000031 SibMessage    W   [:] CWSJY0003W: MQJCA4004: Message delivery to an MDB 'XXX' failed with exception: 'null'

The message endpoint is automatically paused after this error.

I used RFHUtils to get messages send by both JMS and my app and compared them - there is no real difference in UI (except different delivery mode but that is another story) but when I saved messages to file and compared them I saw this difference (just first RFH2 folder):

Send by JMS directly:

<mcd><Msd>jms_text</Msd></mcd>

Send by my app:

<mcd><Msd dt="string" >jms_text</Msd></mcd>

All elements in RFH2 also contains type. Elements from jms folder are in different order but according to exception the problem should be directly with mcd folder. I'm not sure how to better diagnose the issue - I've tried to configure tracing for JMS but I don't know how to do that for WAS (I used WAS on Tuesday for the first time). Standard MQ trace doesn't provide any more information.

My .NET code (WMQ API using MQ Client 7.5 - amqmdnet.dll 7.5.0.0) is quite complex but it generally does:

Receiver

  • Receive MQMessage message by standard Get call on MQQueue accessed with MQOO_INPUT_AS_Q_DEF (no special get options)
  • Read all message headers from received MQMessage
  • Uses GetPropertyNames("%") to get names of all message properties
  • Uses GetObjectProperty to get values for every property
  • If message format is MQSTR reads body by ReadString otherwise by ReadBytes

Sender

  • Creates MQMessage
  • Sets all meaningful message headers from received MQMessage - for example MessageId, ReplyToQueue name and some other are not copied - new or correct values are used instead
  • Sets all properties from received MQMessage by using SetObjectProperty - this step contains some magic because .NET API is inconsistent and the type of value returned from GetObjectProperty is not always accepted by SetObjectProperty - typically I receive String but I must pass int or long (examples: JmsDeliveryMode, JmsPriority or JmsTimestamp). This step also overrides destinations for JmsDestination and JmsReplyTo
  • Write body of the message either by WriteString or WriteBytes
  • Put message to MQQueue accessed with MQOO_OUTPUT (no special put options)

I don't create RFH2 structure manually - I let MQ infrastructure to deal with it. So my question: How to create valid JMS message from .NET which will be accepted by message driven bean?

Note: I don't want to use IBM.XMS - this decision was made long time ago because of some article in IBM knowledge base describing pros and cons of both XMS and WMQ. I need to support both JMS and non-JMS messaging.

1
.netjmswebsphereibm-mq
Can I know what article are you referring to? It's possible that the article is quite old and outdated. There have been number of improvements in XMS .NET since v2.0 to provide a better throughput. You can find the XMS .NET performance report here: www-01.ibm.com/support/… – Shashi
I'm not able to find the article but simply WMQ was recommended for scenarios where communication with legacy systems is required. That is exactly my case. My component must be able to communicate with ANY MQ sender and receiver including JMS, IMS, CICS, etc. – Ladislav Mrnka

1 Answers

1
votes

After enabling WebSphere tracing and using Java Decompiler to check some WebSphere .jar packages I found the reason for the error by a pure chance.

The tracing has shown what values are passed to the failing _parseMcdFolder method:

[8/3/12 12:16:00:199 CEST] 0000003a  > UOW= source=com.ibm.msg.client.wmq.internal.messages.WMQMessageBase method=_parseMcdFolder(String,String,String) (com.ibm.msg.client.wmq.internal.messages.WMQMessageBase) [:] org=IBM prod=WebSphere component=Application Server thread=[WMQJCAResourceAdapter : 0]
          Entry parm0=<mcd><Msd dt="string" >jms_text</Msd></mcd>  parm1=jms_text parm2=<null>
[8/3/12 12:16:00:199 CEST] 0000003a  3 UOW= source=com.ibm.msg.client.jms.internal.JmsSessionImpl org=IBM prod=WebSphere component=Application Server thread=[WMQJCAResourceAdapter : 0]
          (com.ibm.msg.client.jms.internal.JmsSessionImpl) [:/50d450d4] Caught exception: java.lang.NullPointerException in class: com.ibm.msg.client.jms.internal.JmsSessionImpl method: run() <exitIndex: 2>
[8/3/12 12:16:00:199 CEST] 0000003a  1 UOW= source=com.ibm.msg.client.jms.internal.JmsSessionImpl org=IBM prod=WebSphere component=Application Server thread=[WMQJCAResourceAdapter : 0]
          (com.ibm.msg.client.jms.internal.JmsSessionImpl) [:/50d450d4] Tracing exception:
java.lang.NullPointerException
    at com.ibm.msg.client.wmq.internal.messages.WMQMessageBase._parseMcdFolder(WMQMessageBase.java:445)
    at com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.constructProviderMessageFromRFH2(WMQReceiveMarshal.java:341)
    at com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.createProviderMessage(WMQReceiveMarshal.java:447)
    at com.ibm.msg.client.wmq.internal.messages.WMQReceiveMarshal.exportProviderMessage(WMQReceiveMarshal.java:607)
    at com.ibm.msg.client.wmq.internal.WMQConsumerShadow.getMsg(WMQConsumerShadow.java:1115)
    at com.ibm.msg.client.wmq.internal.WMQSyncConsumerShadow.receive(WMQSyncConsumerShadow.java:334)
    at com.ibm.msg.client.wmq.internal.WMQSession.loadMessageReference(WMQSession.java:1082)
    at com.ibm.msg.client.jms.internal.JmsSessionImpl.consume(JmsSessionImpl.java:2847)
    at com.ibm.msg.client.jms.internal.JmsSessionImpl.run(JmsSessionImpl.java:2549)
    at com.ibm.mq.jms.MQSession.run(MQSession.java:860)
    at com.ibm.mq.connector.inbound.WorkImpl.run(WorkImpl.java:172)
    at com.ibm.ejs.j2c.work.WorkProxy.run(WorkProxy.java:399)
    at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java:1604)

So parameters passed to _parseMcdFolder were:

parm0=<mcd><Msd dt="string" >jms_text</Msd></mcd>  parm1=jms_text parm2=<null>

I decompiled the WMQ resource adapter package stored in %WAS_INSTALL%\lib\WMQ\ra\wmq.jmsra.rar and checked the _parseMcdFolder method. Surprisingly the reported line from exception and the method code didn't correspond (there was another method). Also the code of the method should correctly parse the passed parameter.

After a while I checked whole WAS installation directory and I found two occurrences of unpacked resource adapter - one was in root InstalledComponents directory and second was in InstalledComponents directory of the server profile. These resource adapters had different versions:

  • Global: 7.0.1.4-k701-104-110104
  • Profile: 7.0.0.0-k700-L080820

After decompiling the code for version 7.0.0.0-k700-L080820 I found that there is really a bug - accessing not initialized message:

static WMQMessage _parseMcdFolder(String s, String fbClass, String forcedMessageClass)
    throws JMSException
{
    WMQMessage newMessage = null;

    // 350+ lines of code trying to parse s and initialize newMessage
    // but no fallback so newMessage could be null after the processing

    newMessage.isNullMessage = isNullMsgFlag;  // Line 445 - BOOM!
    return newMessage;
}

This bug was fixed in some following version of the adapter but it was not communicated because I didn't find any documentation related to this issue.

After using the newer adapter version the problem was resolved (actually I have moved just to another problem).