Network assignment HELP NEEDED

[jambeard lewistrix]

Hi, I have an assignment due in a couple of weeks and really need some help with it. I have started it allready and all the code I have written is bellow. I'm very new to java and without the help of my lecturer's am finding this assignment quite hard so ANY help would be apreciated.

This is the assignment:

The assignment is about delivering an on-line (airline JavaJet) booking system. The customer should be able to request a departures time table (2 planes leave per day), make reservations, cancel reservations (only the client who has made the reservation), buy tickets, enquire about free places on a flight.

The system will make use of datagram Sockets technology and will consist of a server and multiple clients. You are to implement a simple information server and several client objects. You need not worry about producing a graphical user interface. (If you do it will be worth extra marks).

The functionality of the Client is that it should

Be able to connect to the server and register its IP address as a valid user along with the name of the user in order to join the service.

Be able to remove the user from the service (e.g. when disconnecting to execute log-off command).

Be able to send a message to the server specifying the information required: - request departures time table per day (2 planes leave per day), - make reservation, cancel reservation, buy tickets, enquire about free places on a flight.

Be able to asynchronously receive and display messages from the information server that a plane has just became fully booked. The second urgent message is that a fully booked plane has just had a cancellation and now has seats available (when somebody else cancels the booking). This requirement can only be properly achieved through use of multithreading.

The functionality of the Server is that it should

Keep a record (in some form) of all on-line registered participants and their addresses.

To be able to accept new participant registrations and add them to the active participants list.

To be able to accept requests from client to remove itself from its records (log-off only from the computer it has registered first).
To read the pre-prepared airline time table from a text file consisting of multiple lines with the following format:
JavaJet <flight Number> <day.month.year> <hh.mm> <total number of seats> < reserved seats> <seats available>

To receive messages and perform the actions required (book, un-book, sell tickets, send timetable information to the cleint.
To handle multiple client connections concurrently.
Maintain correctly the list of seats available in the booking system.

At the moment my code dosn't really work. When I connect to the server it starts a thread and then instantly ends it, then the second time it starts it, runs it for one iteration and then ends it, then starts it, runs it for 2 iterations etc. I can't figure out why.

I'm unsure of how to read the timetable from a file and the thing I am most clueless about is how to asynchronously receive and display messages from server to clients.

I also don't understand how to register the client's IP / name with the server and then store it.

Any other general info and help on datagrams and java would REALLY be appreciated. I'm not asking anyone to do this for me!! Just need a little help.

This is the code I have so far. I've only been working on this for about a day.

This is what I have so far for the server:

/* reciever.java */ 
import java.net.*; // for network 
import java.util.*; // for utilities 
import java.io.*; // for streams 
 
public class reciever 
{ 
 
public static void main( String[] argv ) 
{ 
 
setAvaliableSeats( 10 ); 
 
senderThread thread = null; 
InetAddress clientHostName; 
int clientHostPort; 
 
try 
{ 
int portNumber = 3000; 
 
// assume that port to send to is in arg vector 
if( argv.length == 1 ) 
{ 
portNumber = Integer.parseInt( argv[ 0 ] ); } 
 
DatagramSocket socket = new DatagramSocket( portNumber ); 
//socket.setSoTimeout( 0 ); 
 
System.out.println( "ready to receive on " + 
socket.getLocalAddress().toString() + 
" port: " + socket.getLocalPort() ); 
 
while( true ) 
{ 
 
byte[] buffer = new byte[1024]; 
 
DatagramPacket packet = new DatagramPacket( buffer, buffer.length ); 
 
//assume first packet sent is connection reqest from client 
socket.receive( packet ); 
 
//get clients host name and port number 
clientHostName = packet.getAddress(); 
clientHostPort = packet.getPort(); 
 
thread = new senderThread( socket, packet, clientHostName, clientHostPort ); 
thread.start(); 
 
} 
 
} 
catch (IOException ioe) 
{ 
System.out.println("ERROR: " + ioe); 
} 
 
} 
 
public static void setAvaliableSeats( int avaliableSeats ) 
{ 
 
try 
{ 
 
FileWriter fout = new FileWriter("avaliableSeats.txt",false); 
PrintWriter pout = new PrintWriter(fout,true); 
 
pout.println(avaliableSeats); 
pout.close(); 
 
} 
catch( IOException e ) {} 
 
} 
 
} 

This is what I have so far for the client:

/* sender.java */ 
import java.net.*; // for network 
import java.util.*; // for utilities 
import java.io.*; // for streams 
 
public class sender 
{ 
 
static DatagramSocket socket; 
 
public static void main( String[] argv ) 
{ 
 
try 
{ 
 
InetAddress addr = InetAddress.getLocalHost(); 
int sendPortNumber = 4000; 
int portNumber = 3000; 
 
if (argv.length == 2) 
{ 
try 
{ 
addr = InetAddress.getByName(argv[0]); 
portNumber = Integer.parseInt(argv[1]); 
} 
catch (UnknownHostException uh) 
{ 
addr = InetAddress.getLocalHost(); 
} 
} 
 
socket = new DatagramSocket( sendPortNumber ); 
 
while( true ) 
{ 
 
sendMessages( addr, portNumber ); 
receiveMessages(); 
 
} 
 
} 
catch (UnknownHostException uh) 
{ 
System.out.println("ERROR: " + uh); 
System.exit(0); 
} 
catch (IOException ioe) 
{ 
System.out.println("ERROR: " + ioe); 
} 
 

} 
 
public static void sendMessages( InetAddress addr, int portNumber ) 
{ 
 
try 
{ 
 
String request; 
 
//set up buffer for reading user input 
BufferedReader kbd = new BufferedReader(new InputStreamReader(System.in)); 
 
//read in string from user 
System.out.print( "Enter Message: " ); 
request = kbd.readLine(); 
 
//turn string into array of bytes 
byte[] buffer = request.getBytes(); 
 
// now create and send packet 
DatagramPacket packet = new DatagramPacket(buffer,buffer.length,addr,portNumber); 
socket.send(packet); 
 
//tell user packet sent successfully 
System.out.println("Packet data sent"); 
System.out.println(); 
 
} 
catch( IOException e ) {} 
 
} 
 
public static void receiveMessages() 
{ 
 
try 
{ 
byte[] buffer = new byte[1024]; 
 
DatagramPacket receivePacket = new DatagramPacket( buffer, buffer.length ); 
 
socket.receive( receivePacket ); 
 
byte[] receivedMessage = receivePacket.getData(); 
 
System.out.println(); 
System.out.println( "Message received from server: " + receivedMessage ); 
 
} 
catch( IOException e ) {} 
 
} 
 
} 

This is what I have so far for my thread:

/* senderThread.java */ 
import java.net.*; // for network 
import java.util.*; // for utilities 
import java.io.*; // for streams 
 
public class senderThread extends Thread 
{ 
 
DatagramSocket socket = null; 
DatagramPacket packet = null; 
InetAddress clientHostName; 
int clientHostPort; 
 
public senderThread( DatagramSocket socket, DatagramPacket packet, 
InetAddress clientHostName, int clientHostPort ) 
{ 
this.socket = socket; 
this.packet = packet; 
this.clientHostName = clientHostName; 
this.clientHostPort = clientHostPort; 
} 
 
public void run() 
{ 
 
try 
{ 
//Just a little test I used to see if program was reading and 
//writting number of seats to a file... 
int integer = readAvaliable(); 
System.out.println( integer ); 
 
writeAvaliable( 1 ); 
 
integer = readAvaliable(); 
System.out.println( integer ); 
 
System.out.println( "Connected to: " + socket ); 
 
String connected = new String( "Connected to: " + socket ); 
byte[] buffer = connected.getBytes(); 
DatagramPacket sendPacket = new DatagramPacket(buffer,buffer.length, 
clientHostName, 
clientHostPort); 
 
socket.send( sendPacket ); 
 
//For each input client sends, print it along with address + port number 
while( true ) 
{ 
 
receiveMessages(); 
sendMessages(); 
 
} 
 
} 
 
catch (EOFException e) 
{ // socket unexpectedly closed 
System.err.println("Connection to client unexpectedly closed"); 
} 
catch (IOException e) 
{ // error reading client input 
System.err.println("Error reading from socket " + socket); 
} 
finally 
{ 
 
//close the socket used to connect / send packets to client 
 
} 
 
} 
 
public void receiveMessages() 
{ 
 
try 
{ 
System.out.println( "RECEIVING MESSAGES" ); 
 
socket.receive( packet ); 
 
byte[] request = packet.getData(); 
 
System.out.println(); 
System.out.println( "Received " + request); 
System.out.println( "From IP Address: " + packet.getAddress() ); 
System.out.println( "Using Port: " + packet.getPort() ); 
 
} 
catch( IOException e ) {} 
 
} 
 
public void sendMessages() 
{ 
 
try 
{ 
 
System.out.println( "SENDING MESSAGES" ); 
 
String messageString = new String( "Some message" ); 
 
byte[] buffer = messageString.getBytes(); 
DatagramPacket sendPacket = new DatagramPacket(buffer,buffer.length, 
clientHostName, 
clientHostPort); 
 
socket.send( sendPacket ); 
 
} 
catch( IOException e ) {} 
 
} 
 
//read from file number of seats avaliable 
public int readAvaliable() 
{ 
 
int avaliableSeats = 0; 
 
try 
{ 
 
FileReader fin = new FileReader("avaliableSeats.txt"); 
BufferedReader din = new BufferedReader(fin); 
 
String line = din.readLine(); 
avaliableSeats = Integer.parseInt(line); 
 
din.close(); 
 
return avaliableSeats; 
 
} 
catch( IOException e ) {} 
 
return avaliableSeats; 
 
} 
 
//writes to file new number of seats avaliable 
public void writeAvaliable( int amount ) 
{ 
 
try 
{ 
 
int newAmount = ( readAvaliable() - amount ); 
 
FileWriter fout = new FileWriter("avaliableSeats.txt",false); 
PrintWriter pout = new PrintWriter(fout,true); 
 
pout.println(newAmount); 
 
pout.close(); 
 
} 
catch( IOException e ) {} 
 
} 
 
} 

Thanks a lot,

J.

[Norm Radder]

Rather large question.
I suggest you break it up into smaller questions/problems and solve them one at a time.
As an aid to finding problems, add println() statements to your code to show where it is executing and what the contents of key variables is.
Then you can post them so we can see how the program is working.

Good luck.

[Layne Lund]

It will also help you be more organized if you format your code using commonly accepted standards. For example, it is a common convention to indent the group of statements that are enclosed in { and }. This will help you and us both to be able to read your code more easily.

Layne

[jambeard lewistrix]

I do indent my code it's just that when I cut and pasted the code from something it all went a bit wrong! sorry