MDB and Singleton

I have a MDB that receives data from a JSM queue in XML format. After converting the XML to proper Value Objects using JAXB, it calls a DAO.
We have configure the App server (WLS 8.1)to have 10 MDB in the pool.
The DAO is a singleton with a none static private data member that holds the DataSource.
The DAO.add() operation gets connection from the data source and performs the add.
When we put one msg on the JMS queue we see the transaction time in DAO.add() is an about 1 sec.
When we put 30 msgs on the JMS queue we see 10 threads accessing the singleton instance of the DAO.
I was hoping to see the DB transactions started by these 10 threads would be executed in parallel they way threaded operations should behave considering the context switching factor however what I am seeing from the log files is that the DB transactions are serialized meaning they get executed one at a time!!?? Therefore it takes 10 sec for the 10 threads to complete their work. I was expecting to see something like 3 to 4 sec for all 10 thread to complete the add operation.
Anyone has any ideas? Could it be that the Datasource is a private member of the Singleton DAO and each thread who calls the DAO.add() gets queued up to get access to the Data Source?
Any idea would be great.
Thanks.

Thanks for your answer,
So you never load classes then from configuration file? For example lets say you are processing xml message and for each xml message tag name you have in configuration file the appropriate class to handle such a message. Instead of configuration files would you then just store the values in a map of messageTagName to JNDI name?
Thanks
http://www.ellasweddingfavors.com
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EJB 3.0 MDB and transactions

I'm trying to use an XA topic connection factory in my MDB, I was getting a "not supported in this release" error until I added this annotation to my MDB:
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--- BEGIN QUOTE FROM ORACLE DOCS ---
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Example 2-6 @MessageDriven and @MessageDrivenDeployment Annotation for a J2CA Message Service Provider
import javax.ejb.MessageDriven;
import oracle.j2ee.ejb.MessageDrivenDeployment;
import javax.ejb.ActivationConfigProperty;
import javax.jms.Message;
import javax.jms.MessageListener;
@MessageDriven(
activationConfig = {
@ActivationConfigProperty(
propertyName="DestinationName", propertyValue="OracleASjms/MyQueue"
@MessageDrivenDeployment(
activationConfig = {
@ActivationConfigProperty(
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--- END QUOTE FROM ORACLE DOCS ---
So, instead of specifying the resource adapter as I had above, I simply pasted the last bit of annotations from the docs into my MDB, and much to my surprise I learned that you can't have an activationConfig in a @MessageDrivenDeployment
What's the solution?

OK, I got a little further. Everything works now as such
I'm using the XA topic connection factory, I'm using the resource adapter.
BUT, when I set the transaction required attribute on the MDB, I no longer receive messages.
No errors are logged anywhere. Any suggestions?

Java reflection and singletons

Using java reflection and singletons .. anyone seen this being used?

I've solved it
I had a singleton but then it turned out i had to use reflection instead, i tried to used reflection on 3 methods but the session value within was null upon the second method call. Relfection was re-creating the Object.
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MDB and JMS on different servers

Hi,
My MDB is deployed on a different domain from the JMS server. Both are on weblogic.
While deploying weblogic, I m getting an error: Unable to create a connection.
Can anyone give pointers?
I have ensured the following:
1. The JMS server starts before the MDB server
2. The following data is mentioned in weblogic-ejb-jar.xml:
jndi name of the remote queue
provider url--- t3://hostName:port
jndi name of the remote connection factory
is there anyting else that i m missing ?
thanx and regards
Shivraman Giri

Hi,
Thanx for responding.
I will keep in mind these points when I use a foreign JMS provider. T
Right now I m getting problem when the JMS provider is remote but native ie. MDB and JMS are both on Weblogic. This obviates the need to mention Initial Context. Only the provider URL is to be specified.
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regards
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Creating a MDB and Distributed Queue in Clustered env in weblogic 9.2

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<?xml version='1.0' encoding='UTF-8'?>
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Can I recover a damaged SQL Server 2008 database with the undamaged .mdb and .ldf files?

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Hello! try this steps
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finally need to store it as single file like .mpg or some other extention
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Difference between static class and singleton?

Hi I wonder what could be the difference between static methods and singleton?
In singleton at any point of time there will be only one object existing in the JVM. We create singleton to avoid multiple object creation for that class.
If I make all the methods in the class as static also it does the same job. The memory will be allocated once. Even there wont be any object in this case, so time required for object creation also can be saved. looks like more efficient but still why need singleton?
This question is also posted in java programming forum. The thread is as follows:-
[Click on this to visit that thread |http://forum.java.sun.com/thread.jspa?threadID=5278517&tstart=0]
Edited by: murrayb9654 on Mar 25, 2008 8:20 AM

yawmark wrote:
Static class is a realization of singleton pattern.Not in any conventional sense.
~Especially since a static class is completely different from a class with all static methods.

MDBs and Transactions.

Ok,
I am bit confused with how exactly MDBs work with Transactions.
For example,
suppose we have a simple standalone java message producer which sends a message to a Queue. A MDB's onMessage() picks it up.
Let's say the MDB makes some updates to the database and then invokes a method on a stateless session bean which also updates a database.
By default the transaction attribute of the MDB and stateless session bean would be REQUIRED.
If the stateless session bean database update fails, I presume the MDB's database updates also get rolled back.
But, does the message get rolled back? If not when would the message be rolled back?
Does it make any difference if the MDB is a topic or a queue? Does it make any difference if the message producer is a standalone client or
a stateless session bean with it's own transactional behaviour?
Any help appreciated.
Thanks.

The general principle is: if you have a MDB which consumes a message in a transaction, and that transaction is rolled back, then the message is "rolled back". This means that it is put back on the queue or topic. It will then be delivered to the MDB again.
If your MDB calls a session bean then the two can share the same global transaction as you suggest.
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Nigel

Differnece between Cardinality and Singleton for a Context Node

Dear SDN Community,
Can you please tell me what is the difference between the Cardinality and Singleton properties for a context node.
Thanks!
Surya

Hi Surya
Lead selection
Leadselection is the property which is used to get the index of the selected row of the table
"OnLeadSelect" is the method used to fire an action when a row is selected
The Method wdContext.<node>().getLeadSelection() can be used to
find out the index of the selected element.
Cardinality
Any node or attribute that has the context root node as its immediate parent, is known as an independent node or attribute.
Any node or attribute that has some other node as its immediate parent, is known as a dependent node or attribute.
All context nodes are collections.
A node collection is composed of elements, where an element is an aggregation of the nodes immediate children (attributes and/or other nodes).
The cardinality property controls the number of elements a node collection may hold at runtime.
Every context node has a property called Cardinality. This property is composed of two values that
taken together, describe the maximum and minimum number of elements the node collection may hold
at runtime.
Cardinality Minimum: 0 or 1
Cardinality Maximum: 1 or n
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0..1 Zero or one elements permitted
0..n Zero or more elements permitted
1..1 One and only one element permitted
1..n One or more elements permitted
Singleton
All independent nodes are forced to be singletons. This is because the context root node has one and only one element.
Singleton is boolean
TRUE : One instance will be created for all te nodes
FALSE : Every Element in the parent node collection,there will be a distinct instance of the child node.
Why Singleton
-Efficiency
-Less Memory
-Lazy Data Access(Creates instance only when needed,till then it will remain unprocessed)
Supply functions
Supply functions are the mechanism to repopulate child nodes when the lead selection in the parent node
changes. When a singleton child node is declared, you must also write an accompanying supply function.
The Web Dynpro Framework will then automatically call your supply function when the lead selection
in the parent node changes.
Regards
Chaitanya.A

Problems with an MDB and OJMS

I have a problem with MDBs and OJMS/AQ. onMessage() method fires well when a message is enqueued, but it is never dequeued. Messages are well received by MDB, but they remain on AQ table without dequeue. Can anybody help me? Thanks

This is bug: Contaner managed transactions do not work with MDBs in OC4J 9.0.3. Either switch to BMT, or use the 10.0.3 preview on OTN.
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HTH
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MDB and XA

          Thanks for your help Tom,
          It turns out I didn't have a transaction. Took a while to track it down...thanks
          again...
          Tom Barnes <[email protected]> wrote:
          >Hi Allen,
          >
          >Your JDBC configuration looks correct, but I may be wrong. I suggest
          >posting to the JDBC newsgroup for confirmation. It might be
          >helpful if you post your MDB xml descriptors.
          >
          >Is your JDBC call embedded directly in the MDB, or does the MDB invoke
          >it through another EJB or RMI class?
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          >It seems like there may be no transaction even though you set required?
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          >transaction, then call weblogic.transaction.Transaction.getStatusAsString()
          >to
          >see its status.
          >
          >
          >Tom
          >
          >Allen Miller wrote:
          >
          >> I have a transaction 'required' mdb that essentially instantiates a
          >class that
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          >operations
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          >>
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          >per the
          >> doc (as I understand it). The code snippet retrieving the datasource
          >and the config.xml
          >> definitions follow the exception message below.
          >>
          >> weblogic 6.1 on win2000
          >>
          >> any ideas???
          >>
          >> SQL operations are not allowed with no global transaction by default
          >for XA drivers.
          >> If the XA driver supports performing SQL operations with no global
          >transaction,
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          >>
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          >

MDB and transactions

Hello,
I was wondering if anyone else has experienced this problem and/or can suggest a solution...btw, I'm running this on JRun4.
I have a JMS queue that uses a database for the queue. The onMessage method for my MDB is part of a container managed transaction. My onMessage method simply inserts the message into an audit table. I then purposely change the name of the audit table so that my MDB will throw a SQLException.
If I send a single message, a SQL exception is thrown and caught and I roll back the transaction via MessageDrivenContext.setRollbackOnly(). The stdout logs show that after the exception the transaction is rolled back and the message is resent. This sequence occurs repeatedly until I fix the column name and then the message is consumed and inserted in my audit table. This works as I expect.
If I were to send 2 (or more) messages, the same SQL exception occurs for each message and the transaction is rolled back and the message(s) are resent. However, once I fix the table error, I find that those 2 messages were repeatedly consumed and inserted into the audit table (e.g. there were 50+ inserts). In the stdout logs it appears once the database problem is corrected each transaction that was rolled back now ends up commiting leading to repeat consumptions.
Has anyone encountered this? I'm a bit confused as to why, since the rollbacks, resends, and commits appear to work fine when there is only a single message.
Any suggestions? Thanks.

This is only a guess, but I'd say that the implementation isn't using two-phase commit aware resources (XAResources) to coordinate modifications to the backend database table. If you're only using a single resource (message in your case) then it's fine to use raw JDBC and turn auto-commit off; the application or container can then use the JDBC driver commit or rollback operations to make the change to the table happen (or not). If you're doing multiple updates through the same JDBC driver within the same global transaction then this still works.
I wonder if the implementation is somehow adding each message through a separate JDBC instance (even though to the same back end DM) and committing each prior to doing work on the next message. This commit may not be explicit. You may not even know it is going on: for example, if the back end db is Oracle, if you do a close on a JDBC connection which is running in a transaction then it will implicitly commit the transaction at that point.
For instance:
receive message
get JDBC connection
add message to table
close JDBC connection (may be explicit or may be implicit via the container)
<-- commit happens here in some cases
receive message
get JDBC connection
add message to table
What the implementation really should use is XADataSources and XAConnections to get XAResources that coordinate updates to the database. Or, make sure the same JDBC connection is used within the same transaction. This is more difficult to coordinate because of close.

MDB and Database - Listener port stops working

Hi,
I have created an MDB which does the following when a message is received from the queue.
1. Store message in database
2. do some processing
At step 1, if there is any issue with the database connection (e.g. database is not available etc), I rollback transaction. My idea is to leave the message on queue for now and retry it again after some time unless the database is back again. "Maximum retries" of the listener port is set to N but since there is no retry interval available, all N retries are done in a flash and my listener port stops working. I cannot use backout mechanism as I have to wait for the database to be back again. What are my options?

usmanchaudhry wrote:
Hi,
I have created an MDB which does the following when a message is received from the queue.
1. Store message in database
2. do some processing
At step 1, if there is any issue with the database connection (e.g. database is not available etc), I rollback transaction. My idea is to leave the message on queue for now and retry it again after some time unless the database is back again. "Maximum retries" of the listener port is set to N but since there is no retry interval available, all N retries are done in a flash and my listener port stops working. I cannot use backout mechanism as I have to wait for the database to be back again. What are my options?i believe you need an XA driver and a transaction manager, for starters.
a simple JDBC rollback won't do it.
which app server are you using?
which jms provider?
%

MDB and EJB in transactions

Hi ,
          I have an MDB running on weblogic 8.2 and calling a remove ejb running on a different machine. After getting home interface when I tried to create the remote object Iam getting the following error.
          java.lang.NullPointerException
          at weblogic.transaction.internal.PropagationContext.useNewMethod(PropagationContext.java:866)
          at weblogic.transaction.internal.PropagationContext.writeExternal(PropagationContext.java:169)
          at weblogic.common.internal.ChunkedObjectOutputStream.writeObject(ChunkedObjectOutputStream.java:100)
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          at weblogic.rjvm.BasicOutboundRequest.setTxContext(BasicOutboundRequest.java:156)
          at weblogic.rmi.internal.BasicRemoteRef.getOutboundRequest(BasicRemoteRef.java:106)
          at weblogic.rmi.cluster.ReplicaAwareRemoteRef.invoke(ReplicaAwareRemoteRef.java:276)
          at weblogic.rmi.cluster.ReplicaAwareRemoteRef.invoke(ReplicaAwareRemoteRef.java:244)
          Can any body tell what could be the reason. The message sent from MDB to ejb is a transactional message.
          Thanks in advance
          Manikyala

I suggest posting to the EJB newsgroup.
          (1) Transactions certainly are supported for remote services. This is a common use case.
          (2) Your problem seemed to occur when getting the remote home - but likely would not occur when actually using it. Since I think (not 100% sure) that the action of obtaining the remote home need not be transactional, I previously suggested suspending the transactions, but only for the duration of the call to get the remote home.
          Tom
          > Hi Tom,
          >
          > Looks like what Iam doing is not correct.
          >
          > Iam calling a remote ejb which on a different server
          > from my MDB. Iam using t3 to get the context. Also in
          > the weblogic-ejb-jar.xml I put transaction value as
          > Required.
          >
          > Now I replaced that with NotSupported and problem is
          > solved.
          >
          > The conclusion is (if Iam not wrong) when creating a
          > remote home we should not use transactions since the
          > remote service is not participating in transaction.
          >
          > Thanks again Tom
          >
          >
          > Manikyala

MDB and Singleton

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