You will also extend the Hello interface and HelloImpl class to send a Java^TM object MessageObject from the server to the client.

While you are making these changes, take a careful look at MessageObject. It defines both a class variable and an object variable, which are both incremented each time the class is instantiated. By observing how these counters are incremented on the server and client side you can observe that RMI sends object instance information between Java^TM Virtual Machines¹(JVMs), but not the static or class-level information.

The course material for this exercise is covered in Parameters in RMI.

Prerequisites

Simple Banking System

Skeleton Code

Hello.java
HelloImpl.java
MessageObject.java
RMIServer.java
RMIClient.java

Tasks

1. Add the getMessageObject method to the Hello interface.

2. Create an implementation for the getMessageObject method in the HelloImpl class.

3. Compile all of the class files for the server and its remote objects.

4. Create the stub and skeleton files for the remote object implementation.

5. Start the RMI Server in its own DOS console.

6. Start the RMI Client in its own DOS console.

Where help exists, the task numbers above are linked to the step-by-step help page.

Solution Source

Hello.java
HelloImpl.java
MessageObject.java
RMIServer.java
RMIClient.java

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Demonstration

When the server is run in its DOS console, the output will be:

Registry created on host computer <your_computer_name> on port 10002 Remote HelloService implementation object created Bindings Finished, waiting for client requests.

Then when the client is run in its DOS console, the output will be:

HelloService lookup successful The server says: Hello!

printing the message ("Hello!") you defined in your implementation object.

As your client runs both the server console and the client console it prints the instantiation messages from MessageObject. The server console displays:

MessageObject: Class Number is #0 Object Number is #0
MessageObject: Class Number is #1 Object Number is #1
MessageObject: Class Number is #2 Object Number is #2
MessageObject: Class Number is #3 Object Number is #3
MessageObject: Class Number is #4 Object Number is #4
MessageObject: Class Number is #5 Object Number is #5
MessageObject: Class Number is #6 Object Number is #6
MessageObject: Class Number is #7 Object Number is #7
MessageObject: Class Number is #8 Object Number is #8
MessageObject: Class Number is #9 Object Number is #9

While the client console displays:

MessageObject: Class Number is #0 Object Number is #0
MessageObject: Class Number is #0 Object Number is #1
MessageObject: Class Number is #0 Object Number is #2
MessageObject: Class Number is #0 Object Number is #3
MessageObject: Class Number is #0 Object Number is #4
MessageObject: Class Number is #0 Object Number is #5
MessageObject: Class Number is #0 Object Number is #6
MessageObject: Class Number is #0 Object Number is #7
MessageObject: Class Number is #0 Object Number is #8
MessageObject: Class Number is #0 Object Number is #9

Notice the difference in the class numbers.

While the MessageObject instance is moved between the server and the client, the two JVMs load their own, independent copies of the class file. The class variable is incremented on the server, but this is not reflected on the client side.

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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.