If the oracle connection is down in between the application access, i am getting the exception,
"Unidentified SQLException of type: java.sql.SQLException Details: Io exception: End of TNS data channel "

Instead i need to give the user defined message.

In the weblogic console,
the exception thrown is shown below.
<Exception occurred during rollback of transaction Name=[EJB
 com.covansys.jclarety.arch.app.internal.ServiceProviderBean.handleRequest(com.covansys.jclarety.arch.common.api.ServiceRe
quest)],Xid=BEA1-000403B8051EE4727FF9(42158136),Status=Rolled back. [Reason=weblogic.transaction.internal.AppSetRollbackOn
lyException],HeuristicErrorCode=XA_HEURHAZ,numRepliesOwedMe=0,numRepliesOwedOthers=0,seconds since begin=0,seconds left=59
,XAServerResourceInfo[weblogic.jdbc.wrapper.JTSXAResourceImpl]=(ServerResourceInfo[weblogic.jdbc.wrapper.JTSXAResourceImpl
]=(state=rolledback,assigned=myserver),xar=weblogic.jdbc.wrapper.JTSXAResourceImpl@285f9d8,re-Registered = false),SCInfo[S
Sdomain+myserver]=(state=rolledback),properties=({weblogic.transaction.name=[EJB com.covansys.jclarety.arch.app.internal.S
erviceProviderBean.handleRequest(com.covansys.jclarety.arch.common.api.ServiceRequest)], weblogic.jdbc=t3://10.6.95.44:800
1}),OwnerTransactionManager=ServerTM[ServerCoordinatorDescriptor=(CoordinatorURL=myserver+10.6.95.44:8001+SSdomain+t3+, XA
Resources={},NonXAResources={})],CoordinatorURL=myserver+10.6.95.44:8001+SSdomain+t3+): javax.transaction.SystemException:
 Heuristic hazard: (weblogic.jdbc.wrapper.JTSXAResourceImpl, HeuristicHazard, (javax.transaction.xa.XAException: Closed Co
nnection))
        at weblogic.transaction.internal.ServerTransactionImpl.internalRollback()V(ServerTransactionImpl.java:396)
................

ErrorMessage Unidentified SQLException of type: java.sql.SQLException Details: Io exception: End of TNS data channel
Stack Trace: Unidentified SQLException of type: java.sql.SQLException Details: Io exception: End of TNS data channel

Not very sure on what your question is. can you clarify.
Common Oracle exceptions are typically converted to "user-friendly" exceptions.

If I understand correctly, you want to show a meaningful message in this particular error condition. something like "database server was down"
For that, first catch java.sql.SQLException being thrown at this point. Then, find what error code it contains by calling a "getErrorCode()" on your exception object.
I am sure Oralce driver must be populating some particular error code for this scenario. Test if you have that error code. If you see the expected error code, Show meaningful message to user
HTH