Remote Method Invocation (RMI)

Question 1

What are the imports for the RMI interface?

Answer 1

import java.rmi.Remote;

import java.rmi.RemoteException;

Question 2

Give the interface signature

Answer 2

public interface RemoteEcho extends Remote {

Question 3

What exception is thrown by the interface stub

Answer 3

RemoteException

Question 4

What are the imports for the RMI implementation class?

Answer 4

import java.rmi.RemoteException;

import java.rmi.server.UnicastRemoteObject;

Question 5

Give the RMI implementation class signature

Answer 5

class RemoteEchoServant extends UnicastRemoteObject implements RemoteEcho {

Question 6

What is the comment / annotation on RMI implementation methods

Answer 6

@Override

Question 7

What are the imports for the main class on the server side?

Answer 7

import java.rmi.registry.Registry;

import java.rmi.registry.LocateRegistry;

Question 8

Give the first line of the try block on the server

Answer 8

RemoteEcho rei = new RemoteEchoServant();

Question 9

What are the imports for the main class on the client side?

Answer 9

import java.rmi.registry.LocateRegistry;

import java.rmi.registry.Registry;

Question 10

Give the statement to create the registry on the client

Answer 10

Registry reg = LocateRegistry.getRegistry(“localhost”, 1099);

Question 11

Give the statement to create the service on the server

Answer 11

Registry reg = LocateRegistry.getRegistry(“localhost”, 1099);

Question 12

Give the statement to find the service on the registry from the client

Answer 12

Registry reg = LocateRegistry.getRegistry(“localhost”, 1099);

Question 13

Give the statement to bind the registry on the server

Answer 13

reg.rebind(“echoServer”, rei);

Question 14

Give the statement to lookup the registry in the client

Answer 14

Object o = reg.lookup(“echoServer”);

Question 15

Give the first line of the main class in the client

Answer 15

RemoteEcho rei = null;

Question 16

Give the statement to invoke the remote method from the client (reflect)

Answer 16

String s = rei.reflect(buf);

Question 17

What is a callback?

Answer 17

Callback refers to the server’s action of notifying clients about an event

Question 18

How can Callbacks can be implemented in Java RMI?

Answer 18

♦ Client creates a remote object that implements an interface containing a method for the server to call (callback object)
♦ Server provides an operation allowing clients to inform it of the remote object references of their callback objects. It records these in a list
♦ Whenever an event of interest occurs, server calls the interested clients

Question 19

Advantages of Callbacks are :

Answer 19

♦ Server performance does not degrade due to constant polling
♦ Clients can be notified of updates in a timely manner

Question 20

Disadvantages of Callbacks are :

Answer 20

♦ Server needs up-to-date list of clients’ callback objects; clients do not inform the server when they exit; leasing can be used to overcome this problem