/*Define public interface that is an extension of java.rmi.Remote*/
public interface RMIFile extends Remote
{
/*Declare a read() method that takes two arguments and throws a RemoteException*/
String read(int linenum, char passwd) throws RemoteException;
}
RMIFileImpl:
/*Import the following packages to be used in the program*/
import java.rmi.*;
import java.rmi.server.*;
import java.io.*;
/*Declare a public class that extends a UnicastRemoteObjec and implements the RMIFile*/
public class RMIFileImpl extends UnicastRemoteObject implements RMIFile
{
/*Declare a static String object and assign to "localhost"*/
public static final String Host ="localhost";
/*Define a constructor that calls super() and throws a RemoteException*/
public RMIFileImpl() throws RemoteException
{
super();
}
/*Implement the read() method defined in the remote interface*/
public String read(int linenum, char passwd) throws RemoteException
{
try
{
/*Instantiate an String object, and set it to null*/
String ast = null;
/*open a file for reading*/
FileReader fr=new FileReader("hello.txt");
/*wrap the filereader to a bufferedreader*/
BufferedReader frb = new BufferedReader(fr);
/*read one line*/
for(int i=0; i<linenum; i++)
{
ast=frb.readLine();
}
/*Print the message before encryption*/
System.out.println("Before Encryption:"+ast);
/*Encrypt the message*/
char[] aa=ast.toCharArray();
for(int i=0;i<aa.length;i++)
aa[i]=(char)(aa[i]^passwd);
/*Instantiate a String object and store in it the encrypted message stored in the aa array*/
String ooo=new String(aa);
/*Print the message on the screen after the encryption*/
System.out.println("After Encryption:"+ooo);
/*Return the content of the ooo String to requesting Client*/
return ooo;
/*Catch the FileNotFoundException and print an error message on the screen*/
}catch(FileNotFoundException e)
{
System.out.println("file not found");
System.exit(1);
}
/*Catch the IOException and print an error message on the screen*/
catch(IOException e)
{
System.out.println(e);
System.exit(1);
}
/*Return a null value*/
return null;
}
}
RMIServer:
/*Import the following packages to be used in the program*/
import java.rmi.*;
import java.rmi.server.*;
import java.io.*;
/*Declare a public class called RMIServer*/
public class RMIServer
{
/*Declare a static String object and assign to "localhost"*/
public static final String Host ="localhost";
/*Define the main method in program which takes a String array as an argument and throws an Exception*/
public static void main(String args[]) throws Exception
{
try
{
/* Create an instance of the RMIFileImpl*/
RMIFileImpl temp = new RMIFileImpl();
/*Register remote object with RMI registry*/
Naming.rebind("rmi://" +Host+"/RMIFile",temp);
/*Catch the IOException and print an error message on the screen*/
}catch(Exception e)
{
System.err.println(e);
System.exit(1);
}
}
}
RMIClient:
/*Import the following packages to be used in the program*/
import java.rmi.*;
import java.io.*;
/*Define an RMIClient public class*/
public class RMIClient
{
/*Declare a static String object and assign to "localhost"*/
private static final String Host = "localhost";
/*Define the main method in program which takes a String array as an argument and throws an Exception*/
public static void main(String args[])
{
/*If the length of the args array is not equal to two arguments then a error message is printed on the screen*/
if (args.length !=2)
{
System.err.println("usage: java MyApp <linenumber> <character>");
System.exit(1);
}
try{
/*Convert the first received argument from a String to an integer*/
int linenum = Integer.parseInt(args[0]);
/*Create an array in which all the converted Strings to characters are stored*/
char aaa[]=args[1].toCharArray();
/*Select the first element of the aaa array and store it in the passwd object*/
char passwd =aaa[0];
/*If linenum is over 10, then print error message on the screen*/
if (linenum>10)
{
System.err.println("the number should not be over 10");
System.exit(1);
}
/*Construct a link object used to look up a RMIFile remote object*/
RMIFile link = (RMIFile)Naming.lookup("rmi://" +Host +"/RMIFile");
/*look up the remote object in the remote host's registry*/
String result1 = link.read(linenum, passwd);
/*Decrypt the message received from the server*/
char[] bb = result1.toCharArray();
for(int i=0;i<bb.length;i++)
bb[i]=(char)(bb[i]^passwd);
/*Create a String object in which to store the message after the decryption*/
String kkk=new String(bb);
/*Display the message before decryption*/
System.out.println("Before Decryption:" +result1);
/*Display the message after decryption*/
System.out.println("After Decryption:"+kkk);
}
/*Catch the Exception error and print an error message, and exit the system*/
catch (Exception e)
{
System.out.println("The first argument should be a number and the second argument should be a character");
System.out.println(e);
System.exit(1);
}
}
}
TESTING:
A testing procedure was followed to show the program is running and also highlight the error handling procedure implemented in the process:
To show the program running, we first compile all the programs including, RMIFile, RMIFileImpl, RMIClient, RMIServer.
The following steps are followed in order to run the program:
- generate the stub and skeleton:
- Start the RMI registry:
- Run the RMIServer:
When the RMIServer is prompted by the client to return a file, it responds in the following manner showing the message before encryption and after encryption:
- We then run the RMIClient program and give two arguments a number and a letter to encrypt the message with, the file is then returned in an encrypted format, and it gets decrypted and displayed on the screen.
If a different letter is entered by the user, then the encryption changes accordingly:
If a different number is entered, then the file with the correct number gets extracted and displayed on the screen:
ERROR HANDLING:
The user might provide a wrong input, in which case the program should be able to handle such cases and display an error message, this section will cover such occurrences.
- If the user provides a character instead of a number in the first argument then the following message is displayed and the program is stopped:
- If the user enters a number over 10, then the following message is displayed, prompting the user to enter a number that is not over than 10.
