Corba IDL in Java

CORBA & IDL in Java last reivision Nov 22 / 2000 Peter Komisar

1. Define the interface for the services and structure of the remote Corba object

module vote_poll{
    interface votes{
         long get_Liberal( );
         long get_Tory( );
         };
      };

2. Save to an .idl file and compile it with the idltojava compiler

idltojava -fno-cpp vote_poll.idl // leaving out the no pre-proccessor flag resulted in a fatal error

A new directory called vote_poll is created (in the current dir), containing the java files
votes.java, _votesStub.java, _votesImplBase.java, votesHolder.java, votesHelper.java

Here what you get. . .

votes.java       //   The java interface extending org.omg.CORBA..Object and IDLEntity

/*
* File: ./VOTE_POLL/VOTES.JAVA
* From: VOTE_POLL.IDL
* Date: Mon Nov 22 15:04:16 1999
*   By: C:\JDK12~1.2\BIN\IDLTOJ~1.EXE Java IDL 1.2 Aug 18 1998 16:25:34
*/
package vote_poll;
public interface votes
extends org.omg.CORBA.Object, org.omg.CORBA.portable.IDLEntity {
// notice extensions added by idltojava
    int get_Liberal( );
    int get_Tory( );
}

_votesImplBase.java // this implementation class which is mercifully extendable. Take a look!

_votesStub.java    // the stub for the client acts as a proxy to make calls on the remote Corba object

votesHolder.java          // assists in method calls which are not supported by java

votesHelper.java           // provides methods to help the client resolve the remote object

3. Compile the generated java files

javac vote_poll \ *.java

Implementation Class

4. Create the implementation class extending the _nameImplBase

package vote_poll;

public class votesImpl extends _votesImplBase{
   static int l = 0;
   static int t = 0;
   public votesImpl( ){       // recommended no-arg, empty constructor
   }
     /* method implementations */
public int get_Liberal( ){
   l ++ ;
return l ;
}
public int get_Tory( ){
t ++ ;
return t;
}
}
                 // The class compiled but there were a lot of method deprecation

Corba Server

5. Writing the server.
Looking at a several examples, code for the corba server is all quite similar

import vote_poll.*;
import org.omg.CosNaming.* ;
import org.omg.CosNaming.NamingContextPackage.* ;
import org.omg.CORBA.* ;

public class vote_poll_server {
public static void main( String args[] )
{
try{
// initialize ORB instance
ORB orb = ORB.init(args,null);

    // instantiate implementation object and register with ORB
     votesImpl vI = new votesImpl( );
     orb.connect(vI);

     // reference the name service
     org.omg.CORBA.Object corba_object = orb.resolve_initial_references("NameService");
     NamingContext naming_context = NamingContextHelper.narrow(corba_object);

    // Bind the implementation object reference to a naming component
     NameComponent namecomponent = new NameComponent("Vote", "");
     NameComponent path[] = { namecomponent };
     naming_context.rebind(path, vI);

      // Synch on Object object and wait for client invocations
     java.lang.Object sync = new java.lang.Object( );
     synchronized (sync) {
     sync.wait( );
     }
     }
     catch(Exception e){
       System.err.println("Error " + e);
       }
   }
}

Corba Client

6. Writing the client

import vote_poll.* ;
import org.omg.CosNaming.* ;
import org.omg.CosNaming.NamingContextPackage.* ;
import org.omg.CORBA.* ;

public class vote_poll_client{
public static void main( String args[] ){

if (args.length!=1){
     System.out.println("Vote by specifying a party, Liberal or Tory. ");
     System.exit(1);
     }
     String party_vote=args[0];
try{
   // Create and initialize an instance of an ORB
      ORB orb = ORB.init(args, null);

   // Obtain a Name Service reference
      org.omg.CORBA.Object corba_object = orb.resolve_initial_references("NameService");
      NamingContext naming_context = NamingContextHelper.narrow(corba_object);

   // Creates a name component object for String "Vote" , then an array of one of it
      NameComponent nc = new NameComponent( "Vote", "");
      NameComponent path[] = { nc };

/*    The object returned by the Helper class narrow method is assigned to the implementation
         interface. The object returned is actually a stub object (_votesStub generated by the idltojava
         compiler) which acts as a proxy or representative for the actual implementation referenced
        back at the server
*/
        votes vI = votesHelper.narrow(naming_context.resolve(path));

// reference the interface methods against the implementation stub object, vI
      if (party_vote.equals("Liberal"))
         System.out.println( "The vote is Liberal and the new tally is " + vI.get_Liberal());
      else
          if (party_vote.equals("Tory"))
            System.out.println( "The vote is Tory and the new tally is " + vI.get_Tory());
          else
            System.out.println("Your ballot has been discounted");
   }
   catch(Exception e)
   {
   System.out.println("ERROR : " + e);
   }
}
}

7. Compile the Server and the Client and the Implementation class

// cd to the directory above vote_poll

    javac vote_poll \ vote_poll_client.java
    javac vote_poll \ voteImpl.java
    javac vote_poll \ vote_poll_server.java

8. Run the name server

Enter tnameserv at the command line

// Move the client and the server to a directory above the vote_poll directory.
// This allows the contents of the directory corresponding to vote_poll to be imported

9. Run the server

java vote_poll_server

10. Run the client

java vote_poll_client