Issue 2479:  Use of "java" as top-level IDL module (java2idl-rtf)
Source:  (, )
Nature:  Uncategorized Issue
Severity: 
Summary: Summary: The Java to IDL mapping specifies a number of names in the IDL
 module "java".  Examples are ::java::lang::Exception and
 ::java::lang::_Object.  This can cause problems when mapping
 Java to IDL and then remapping the resulting IDL back to Java.
 

Resolution: Closed, no change
Revised Text: 
Actions taken:
February 22, 1999: received issue
June 4, 1999: closed issue
Discussion: 

End of Annotations:=====
Date: Mon, 22 Feb 1999 13:52:52 +0000
From: Simon Nash <nash@hursley.ibm.com>
Organization: IBM
To: issues <issues@omg.org>
CC: java2idl <java2idl-rtf@omg.org>
Subject: Use of "java" as top-level IDL module

The Java to IDL mapping specifies a number of names in the IDL
module "java".  Examples are ::java::lang::Exception and
::java::lang::_Object.  This can cause problems when mapping
Java to IDL and then remapping the resulting IDL back to Java.

This issue is only about the choice of names in the Java to IDL
mapping, not about the wider implications of this Java->IDL->Java
scenario.  The names that may need to be changed if we decide that
some action is needed are as follows:
  ::java::lang::Exception
  ::java::lang::_Object
  ::javax::rmi::CORBA::ClassDesc
  ::java::io::Serializable
  ::java::io::Externalizable

To avoid conflict with built-in JDK classes of similar names to 
the above, it is necessary to specify a package prefix for the 
"java" module when mapping generated IDL back to Java.  This has 
the unfortunate side-effect of mapping all IDL valuetypes that 
started life as JDK classes back to similar but different classes 
in generated Java code.  For example, if the package prefix for
"java" is "gen", then the java.util.Date class will map back to
gen.java.util.Date.  This requires the user to implement 
gen.java.util.Date as a wrapper for java.util.Date.

For many users, this is confusing and annoying.  They would like
to be able to use the original java.util.Date class.  There are
many issues with supporting this use, and it would probably require
some changes in the IDL to Java mapping of valuetypes.  However,
there is little point in enabling this round trip mapping if the
names of a small number of classes in the Java to IDL mapping spec
effectively prevent its use for all JDK classes.

Since a top-level OMG-defined IDL module is needed for these names,
an obvious solution is to put them under the top-level CORBA module.
For example:
  ::CORBA::java::Exception
  ::CORBA::java::_Object
  ::CORBA::java::ClassDesc
  ::CORBA::java::Serializable
  ::CORBA::java::Externalizable

The alternative is to do nothing and say that this round-tripping
is not supported, as we do today.  However, I have been convinced
by user feedback from the RMI-IIOP beta that this is not a good
enough answer.

   Simon
-- 
Simon C Nash, Technology Architect, IBM Java Technology Centre
Tel. +44-1962-815156   Fax +44-1962-818999    Hursley, England
Internet: nash@hursley.ibm.com   Lotus Notes: Simon Nash@ibmgb