Welcome to jGuru.com exercises for the Fundamentals of RMI short course.

These exercises illustrate the use of the Remote Method Invocation (RMI) library for implementing distributed objects.

When you finish these exercises, you will have a good idea of the essential concepts involved in building RMI-based distributed Java systems. With this foundation, you will be able to design and implement dsophisticated, multi-computer Java^TM programs.

Exercise Outline

• About Exercises
  • The Anatomy of an Exercise
  • Exercise Design Goals

• Fundamentals of RMI Exercises
  1. UML Definition of RMI Example System
  2. Simple Banking System
  3. RMI Parameters
  4. RMI Client Callbacks
  5. Bootstrap Example
  6. Distributed Garbage Collection
  7. Serializing Remote Objects: Server
  8. Serializing Remote Objects: Client

About Exercises

The Anatomy of an Exercise

• Help: Gives you help or hints on the current exercise, an annotated solution. For ease of use, the task information is duplicated on the help page with the actual help information indented beneath it.
• Solution: The <applet> tag and Java source resulting in the expected behavior.
• API Documentation: A link directly to any necessary online API documentation.

Exercise Design Goals

"Blank screen"

You are confronted with a "blank screen" and you create the entire desired functionality yourself.

Extension

You extend the functionality of an existing, correctly-working program.

Repair

You repair undesirable behavior in an existing program.

To make learning easier, exercises, where possible, address only the specific technique being taught in that exercise. Irrelevant, unrelated, and overly complex materials are avoided.

Where possible, exercises execute via the web. However, exercises that must access Java features or library elements that could cause security violations are not executed on the web.

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Fundamentals of RMI Exercises

1. UML Definition of RMI Example System

   This exercise will introduce you to the definition of RMI remote services using Java interfaces.

   Educational goals:

   • Introduce the UML Description of a banking system
   • Complete the Java source code for the system interfaces
2. Simple Banking System

   In this exercise you will run your first RMI system. It is based on the Banking System that you started in the previous exercise.

   Educational goals:

   • Learn to run the RMI Registry as a separate process
   • Run a server that support remote RMI objects
   • Implement an RMI client that uses remote services.
3. RMI Parameters

   When a remote method is called, parameters may be passed to the remote object and a return value may be sent back to the calling program. This exercise explores how RMI handles primitive data types, normal local Java objects, and remote RMI objects as parameters and return values.

   Educational goals:

   • Practice defining and implementing remote interfaces and their implementations.
   • Learn how remote objects and normal objects are passed as parameters.
4. RMI Client Callbacks

   In some RMI systems, it will make sense for a server to make calls to a client program. This can be done using client-side callbacks.

   It is very easy to build client-side callbacks with RMI. One simply creates a client-side remote object and gives a reference to it to the server. The server then uses this remote reference to call into the client's program.

   Educational goals:

   • Learn how to create client-side remote objects.
   • Prepare and export remote objects that do not directly extend java.rmi.server.UnicastRemoteObject
5. Bootstrap Example

   This exercise has three components: bootstrap HTTP Server, bootstrap RMI Server and bootstrap RMI Client. They will highlight how RMI supports the distributed, on-demand loading of class files via FTP and HTTP servers.

   To start with, you will first run a simple server that delivers Java class files through the HTTP protocol.

   Next, you will create and run the bootstrap RMI Server. The server is very similar to other RMI Servers you have run. One of the main differences in this example is that the RMI client code is located in the same directory as the server. It will be up to the HTTP Server to deliver the client classes to the client computer.

   Finally, you will create a very thin client program. The sole purpose of this program is to start and then request the 'real' client software from the network. The requests for Java classes will be serviced by the HTTP Server that you ran earlier in the exercise.

   Educational goals:

   • Observe an HTTP Server supplying classes to an RMI system
   • Observe how to write a simple HTTP Server
   • Create and run an RMI Server program
   • Build a bootstrap program to load the client program over the network
   • Run the Bootstrap Client and observe how the HTTP Server program reports which classes have been requested and supplied
   • Learn about the java.rmi.server.codebase system property
6. Distributed Garbage Collection

   The Distributed Garbage Collector and the local Java garbage collector work together to manage heap memory space in each Java^TM Virtual Machine¹(JVM) that participate in an RMI system. In this exercise, you will have the opportunity to experiment with an RMI Server and two RMI Clients to observe how memory is managed.

   Educational goals:

   • Observe the behavior of the Distributed Garbage Collector.
   • Observe the interaction of the local and distributed garbage collectors.
   • Experiment with different settings for the Java heap and notice how it affects the operation of the two garbage collectors.
7. Serializing Remote Objects: Server

   This exercise illustrates how to use the Delegation Pattern to create a system that will allow a network service to migrate between a local machine JVM and the remote server.

   This is a simple version of a Delegation architecture. More sophisticated architectures can be build by expanding on this example.

   This is a two-part exercise. Run the server first and then the client to complete the example.

   Educational goals:

   • Understand how RMI limits the ability to move remote objects between JVMs.
   • See how to use the Delegation Pattern to overcome this limitation.
8. Serializing Remote Objects: Client

   The client program will request both a remote reference to a service and a local copy of an object that implements the service.

   Educational goals:

   • See how to build an RMI client that uses either a remote reference to a service or a local copy.

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¹ As used on this web site, the terms "Java virtual machine" or "JVM" mean a virtual machine for the Java platform.