Developing a CORBA Client which uses DII by Gopalan Suresh Raj

Developing a CORBA Client which invokes a CORBA Server using
The Dynamic Invocation Interface (DII)
Gopalan Suresh Raj

What happens if the Java interfaces for the remote CORBA Object servers are not available at compile time? You might get a reference to a CORBA Object from a Naming Service, and not know what interface that object implements. Both the Dynamic Invocation Interface (DII) and the Dynamic Skeleton Interface (DSI) API in CORBA provide "A Dynamic Interface to a CORBA Object whose interface is not known at compile time to the client of the CORBA Object".

The Steps involved in developing a CORBA Client that invokes a CORBA Server dynamically using the Dynamic Invocation Interface are:

1. Implement your CORBA client application which uses DII to call the Server component

StockMarketClient.java

// StockMarketClient using DII
import org.omg.CORBA.*;
import org.omg.CosNaming.*;

public class DIIStockMarketClient {

public static void main (String[] args) {

ORB myORB = ORB.init (args, null);
ORB singleORB = ORB.init ();

try {

   // Get a reference to the object
   org.omg.CORBA.Object ncRef = myORB.resolve_initial_references ("NameService");
   NamingContext nc = NamingContextHelper.narrow (ncRef);
   NameComponent nComp = new NameComponent ("NASDAQ", "");
   NameComponent [] path = {nComp};
   org.omg.CORBA.Object objRef = nc.resolve (path);

   // Now make a dynamic call to the get_price method. The first step is
   // to build the argument list. In this case, there's a single String
   // argument to the method, so create an NVList of length 1. Next
   // create an Any object to hold the value of the argument and insert
   // the desired value. Finally, wrap the Any object with a NamedValue
   // and insert it into the NVList, specifying that it is an input
   // parameter.
   NVList argList = myORB.create_list (1);
   Any argument = myORB.create_any ();
   argument.insert_string ("MY_COMPANY");
   NamedValue nvArg = argList.add_value ("symbol", argument, org.omg.CORBA.ARG_IN.value);

   // Create an Any object to hold the return value of the method and
   // wrap it in a NamedValue
   Any result = myORB.create_any ();
   result.insert_float (0);
   NamedValue resultVal = myORB.create_named_value ("result", result, org.omg.CORBA.ARG_OUT.value);

   // Create the method request using the default context, the name of
   // the method, the NVList argument list, and the NamedValue for the
   // result. Then invoke the method by calling invoke () on the Request.
   Request thisReq = objRef._create_request (null, "get_price", argList, resultVal);
   thisReq.invoke ();

   // Get the return value from the Request object and output results.
   result = thisReq.result().value ();
   System.out.println ("get_price () returned: " + result.extract_float ());

}
catch (Exception e) {
   e.printStackTrace ();
}

}
}

About the Author...

Gopalan Suresh Raj is a Software Architect, Developer and an active Author. He is contributing author to a couple of books "Enterprise Java Computing-Applications and Architecture" (Cambridge University Press, June '99) and "The Awesome Power of JavaBeans" (Manning, July'98). His expertise spans enterprise component architectures and distributed object computing. Visit him at his Web Cornucopia^© site (http://www.execpc.com/~gopalan) or mail him at gopalan@execpc.com.