Programming Stand-alone Clients

Developing T3 Clients

A T3 client is an RMI client that uses BEA’s proprietary T3 protocol to communicate with WebLogic server instance.

The following sections provide information on developing T3 clients:

T3 Client Basics

A T3 client:

Developing a T3 Client

Creating a basic T3 client consists of the following

Sample code to for a simple T3 client is provided in Listing 3-1.

package examples.rmi.hello;

import java.io.PrintStream;
import weblogic.utils.Debug;
import javax.naming.*;
import java.util.Hashtable;

/**
* This client uses the remote HelloServer methods.
*
* @author Copyright (c) 1999-2004 by BEA Systems, Inc. All Rights Reserved.
*/
public class HelloClient {

private final static boolean debug = true;

/**
* Defines the JNDI context factory.
*/
public final static String JNDI_FACTORY="weblogic.jndi.WLInitialContextFactory";

int port;
String host;

   private static void usage() {
   System.err.println("Usage: java examples.rmi.hello.HelloClient " +
      "<hostname> <port number>");
   System.exit(-1);
   } 

   public HelloClient() {}

   public static void main(String[] argv) throws Exception {
      if (argv.length < 2) {
      usage();
     }
   String host = argv[0];
   int port = 0;
   try {
      port = Integer.parseInt(argv[1]);
      }
   catch (NumberFormatException nfe) {
      usage();
      }
   try {

      InitialContext ic = getInitialContext("t3://" + host + ":" + port);

      Hello obj = 
         (Hello) ic.lookup("HelloServer");
      System.out.println("Successfully connected to HelloServer on " +
         host + " at port " +
         port + ": " + obj.sayHello() );
      }
   catch (Throwable t) {
      t.printStackTrace();
      System.exit(-1);
      }

  }

   private static InitialContext getInitialContext(String url)
      throws NamingException
   {
   Hashtable env = new Hashtable();
   env.put(Context.INITIAL_CONTEXT_FACTORY, JNDI_FACTORY);
   env.put(Context.PROVIDER_URL, url);
   return new InitialContext(env);
   }
}

RMI Communication in WebLogic Server

RMI communications in WebLogic Server use the T3 protocol to transport data between WebLogic Server and other Java programs, including clients and other WebLogic Server instances. A server instance keeps track of each Java Virtual Machine (JVM) with which it connects, and creates a single T3 connection to carry all traffic for a JVM. See Configure T3 protocol in Administration Console Online Help.

For example, if a Java client accesses an enterprise bean and a JDBC connection pool on WebLogic Server, a single network connection is established between the WebLogic Server JVM and the client JVM. The EJB and JDBC services can be written as if they had sole use of a dedicated network connection because the T3 protocol invisibly multiplexes packets on the single connection.

Determining Connection Availability

Any two Java programs with a valid T3 connection—such as two server instances, or a server instance and a Java client—use periodic point-to-point “heartbeats” to announce and determine continued availability. Each end point periodically issues a heartbeat to the peer, and similarly, determines that the peer is still available based on continued receipt of heartbeats from the peer.

Communicating with a Server in Admin Mode

To communicate with a server instance that is in admin mode, you need to configure a communication channel by setting the following flag on your client:

   -Dweblogic.AdministrationProtocol=t3