[SOLVED] CS Java distributed system COMP2121 Lab 4 Remote Method Invocation

COMP2121 Lab 4 Remote Method Invocation
The goal of this lab is to make an object remotely accessible. The machine where the object is located plays the role of the server. Client machines will be able to invoke methods of this object remotely. The work is divided into four consecutive exercises.
Make sure to run Linux on your computer or reboot it.
Exercise 1: Remote Object Interface
The first task is to write the server interface indicating the methods that can be invoked remotely. This interface should be present both at the client and server sides.
A necessary package is java.rmi. You have to implement a RemoteCounter interface specifying the behaviour of an object that extends the Remote interface. It simply consists of a method inc taking no argument and returning an int.
Duration: 10 min
Exercise 2: Server Implementation of the Interface
This task consists in writing the RemoteCounterImpl implementation of the previous counter in- terface. It will simply export an inc method that takes no argument but returns as an int the incre- mented counter value.
However, as a remote object it should be available remotely. The simplest solution consists in ex- tending the java.rmi.UnicastRemoteObject class. (It defines various constructors and static methods to make remote objects available. By construction, such objects will be automatically made available and standard sockets will be used transparently for communication.)
1
2 public class RemoteCounterImpl extends UnicastRemoteObject implements RemoteCounter { 3
For simplicity, this implementation will also contain the main method that creates the server. It noti- fies the name server of the server-side machine of the existence of the counter object using the static methods of java.rmi.Naming. Actually, the name server associates a name, THE_SERVER_NAME in the example below, to the remote object. Choose an appropriate name.
1 public static void main(String args[]) { 2
1

3 // Bind this object instance to the name RMICounterObject
4 Naming.rebind(THE_SERVER_NAME, counterServer);
5
6}
Duration: 15 min
Exercise 3: The RMI Client
First, the client has to contact the name server to obtain the remote stub of the Remote object. This is achieved using the static lookup method of the class Naming and referring to the right object name using a URL of the form: rmi://host:port/name.
By default you can use, rmi://127.0.0.1/THE_SERVER_NAME to refer to the local machine with default port 1099. Once you create a new instance of the server, simply print the result returned by its inc method on the standard output.
Duration: 15 min
Exercise 4: Invoking the Remote Method
First, try to make the RMI client connect to the server on the local machine. To make sure the counter server registers itself to the name server, the name server rmiregistry must be started first. This can be done as follows on unix-like machines (under Windows, use start rmiregistry or rmiregistry &fromyourclasspathfolder):
1 $ remiregistry &
Then, executes the counter server in the background before running the client.
After you made the RMI work on the local machine, make sure to kill the rmiregistry and the counter server. Copy the files onto a remote machine and update the server IP address to which the client connects to before re-invoking the method from a remote machine.
Duration: 10 min
COMP2121 Remote Method Invocation
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