tcp/ip socket server in java - Overclock.net

adramalech707 · 05-27-09

okay i need some help i have to main methods one is the server the other is the client i have finished coding them....it is a pretty simple procedure but i am thinking of it like i would if i did it in c....where i have two main methods and i run the server i then run the client.....and then until the client is up and sends something then the server will wait in limbo....and visa versa...once the server is up and the client is up and the client sent its okay status the server will send the request for a number and will then wait for a return....atleast this is the plan

it will then repeat until i send bye...

here is my server code so far:

Code:

package server;

import java.net.*;
import java.util.*;
import java.io.*;

public class Server_Socket {
	//setup constants
	protected static final int PORT_NUM = 5000;
	protected static final int BACKLOG = 5;
	
	public static void main(String[] args) {
		//declare variables to null
		ServerSocket server = null;
		Socket incoming = null;
		BufferedReader in = null;
		PrintWriter out = null;
		boolean done = false;
		String newLine = null;
		int num = 0;
		
		//create a socket and binds it
		try{
			server = new ServerSocket(PORT_NUM, BACKLOG, InetAddress.getLocalHost() );
		}
		catch(Exception e){
			System.out.println("Incountered an error in creating the server socket: " + e);
		}
		
		//accept the client
		try{
			incoming = server.accept();
		}
		catch(Exception e){
			System.out.println("Incountered an error in accepting the client: " + e);
		}
		
		//send and receive data
		try{
		    in = new BufferedReader
		      (new InputStreamReader(incoming.getInputStream()));
		    out = new PrintWriter
		      (incoming.getOutputStream(), true /* autoFlush */);
		    Scanner scan = new Scanner(in);
		    
		    //wait till we get a ready status
		    while(newLine.compareTo("Ready") == 0){
		    	newLine.wait(100);
		    	newLine = in.readLine();
		    }
		    
		    //reset newLine
		    newLine = null;
		    
		    //send to client that it is ready to take the number...
		    while(!done){
		    	out.write("Please enter a number to be squared: ");
		    	
		    	//again wait till we get a return
		    	while(newLine == null){
		    		newLine.wait(100);
		    		newLine = in.readLine();
		    	}
		    	
		    	if(newLine != null){
		    		if(newLine.compareTo("Bye") != 0){
		    			num = scan.nextInt();
		    			num = num^2;
		    			out.write(num);
		    		}
		    		else{
		    			done = true;
		    		}
		    	}
		    	else{
		    		done = true;
		    	}
		    }
		}
		catch(Exception e){
			System.out.println("There was an error in receiving or sending data: " + e);
		}
		
		//we are done so close connections
		try{
			incoming.close();
		}
		catch(Exception e){
			System.out.println("Was unable to close, either the connections where cut or connection timed out " + e);
		}
	}
}

here is my client code:

Code:

package client;
import java.net.*;
import java.util.*;
import java.io.*;

public class Client_Socket {
	protected static final int PORT_NUM = 5000;
	protected static final String MACHINE = "localhost";

	public static void main(String[] args) {
		Socket The_Client = null;
		String line = null;
		int num = 0;
		//create a socket and connect
		try{
			The_Client = new Socket(MACHINE, PORT_NUM);
		}
		catch(Exception e){
			System.out.println("There was a " + e + " error in connecting to the server! Please try again.");
		}
		
		//Send and or receive data
		try{
		    BufferedReader in = new BufferedReader
		      (new InputStreamReader(The_Client.getInputStream()));
		    PrintWriter out = new PrintWriter
		      (The_Client.getOutputStream(), true /* autoFlush */);
		    Scanner scan = new Scanner(System.in);	
		    
		    //send it is ready to receive the query
		    out.write("Ready");
		    
		    //this is waiting for server to return the number then closes else will stay open
			while(num != 999){
				if(line == null){
					line.wait(100);
					line = in.readLine();
				}
			    else{
			    	if(line.length() > 3){
			    		System.out.println("This is the result: " + line);
			    	}
			    	else{//it asked to enter a number...
			    		System.out.println(line);
			    		num = scan.nextInt();
			    		if(num != 999){
			    			out.write(num);
			    		}
			    	}
			    }
			}
		}
		catch(Exception e){
			System.out.println("There was an error in sending or receiving data " + e);
		}
		
		//close the socket and output input stream
		try{
			The_Client.close();
		}
		catch(Exception e){
			System.out.println("There was an error in closing the server, " + e);
		}
	}
}

here is my output to console when i run server first then i run client right after i hit run server...

Code:

There was a java.net.ConnectException: Connection refused: connect error in connecting to the server! Please try again.
There was an error in sending or receiving data java.lang.NullPointerException
There was an error in closing the server, java.lang.NullPointerException

i am wondering what i should do???? i am just trying to learn this on java through eclipse ide....i know how to do it in c and it is more complex with having to run 5 different instances and running rcpgen etc....

this seems to be less complex but more of a hassle....

how do i run two main methods in two different classes at once in the same project...can i just make one main method to run both main methods???

or do i need to manually run each class???

**EDIT:
okay so i just ran the server and let it run and it just sat there and did nothing waiting till the client was ran...

so i take it the server so far is doing its job...i will put in alot of println's to have the ability to follow what happens...

adramalech707 · 05-29-09

okay so i seem to get pretty far....i atleast know that i create the socket on client and server...and that the server does accept the client...

the issue i am at right now...is writing to the out stream and then checking the in stream on the other side to see if out stream wrote anything so i can take the number and square it....so here is the code right now....

now i know i shouldn't be using the sleep method as how i have it setup it will just lag out the cpu..but since the variable i am using can be null the first time through i cannot tell wait on a null variable without getting null pointer exception...

another thing is if i am actually doing the right thing with the i/o stuff???

i did find a way to have the client in one workspace and the server in another and run to instances of eclipse ide actually allowed me to see how far on each side they got before crashing....the server was good but i cannot tell if it actually executed the out.write line where it asks for a number.... because when i go to the client while debugging after a couple loops the in stream is still null.....

the client

Code:

package client;
import java.net.*;
import java.util.*;
import java.io.*;

public class Client_Socket {
	protected static final int PORT_NUM = 5000;
	
	private static void sleep(int num){
		int i = 0;
		while(i <= num){
			i++;
		}
	}
	
	public static void main(String[] args) {
		Socket The_Client = null;
		String line = null;
		int num = 0;
		
		//create a socket and connect
		try{
			The_Client = new Socket(InetAddress.getLocalHost(), PORT_NUM);
			System.out.println("Client is connected to the server!");
		}
		catch(Exception e){
			System.out.println("There was a " + e + " error in connecting to the server! Please try again.");
		}
		
		//Send and or receive data
		try{
		    BufferedReader in = new BufferedReader
		      (new InputStreamReader(The_Client.getInputStream()));
		    PrintWriter out = new PrintWriter
		      (The_Client.getOutputStream(), true /* autoFlush */);
		    Scanner scan = new Scanner(System.in);
		
		    //this is waiting for server to return the number then closes else will stay open
			while(num != 999){
				if(line == null){
					sleep(100);
					line = in.readLine();
				}
			    else{
			    	if(line.length() > 3){
			    		System.out.println("This is the result: " + line);
			    	}
			    	else{//it asked to enter a number...
			    		System.out.println(line);
			    		num = scan.nextInt();
			    		if(num != 999){
			    			out.write(num);
			    		}
			    	}
			    }
			}
		}
		catch(Exception e){
			System.out.println("There was an error in sending or receiving data " + e);
		}
		
		//close the socket and output input stream
		try{
			The_Client.close();
		}
		catch(Exception e){
			System.out.println("There was an error in closing the server, " + e);
		}
	}
}

the server

Code:

package server;
import java.net.*;
import java.util.*;
import java.io.*;

public class Server_Socket {
	//setup constants
	protected static final int PORT_NUM = 5000;
	protected static final int BACKLOG = 5;
	
	private static void sleep(int num){
		int i = 0;
		while(i <= num){
			i++;
		}
	}
	
	public static void main(String[] args) {
		//declare variables to null
		ServerSocket server = null;
		Socket incoming = null;
		BufferedReader in = null;
		PrintWriter out = null;
		boolean done = false;
		String newLine = null;
		int num = 0;
		
		//create a socket and binds it
		try{
			server = new ServerSocket(PORT_NUM, BACKLOG, InetAddress.getLocalHost() );
			System.out.println("Server has been connected ");
		}
		catch(Exception e){
			System.out.println("Incountered an error in creating the server socket: " + e);
		}
		
		//accept the client
		try{
			incoming = server.accept();
			System.out.println("The server accepts the client!");
		}
		catch(Exception e){
			System.out.println("Incountered an error in accepting the client: " + e);
		}
		
		//send and receive data
		try{
		    in = new BufferedReader
		      (new InputStreamReader(incoming.getInputStream()));
		    out = new PrintWriter
		      (incoming.getOutputStream(), true /* autoFlush */);
		    
		    //send to client that it is ready to take the number...
		    while(!done){
		    	out.write("Please enter a number to be squared, or 999 to quit: ");
		    	
		    	//again keep checking till we get a return
		    	while(newLine == null){
		    		sleep(100);
		    		newLine = in.readLine();
		    	}
		    	if(newLine.compareTo("Bye") != 0){
		    		try{
		    			num =  Integer.parseInt(newLine.trim());
		    			num = num^2;
		    			out.write(num);
		    		}
		    		catch(NumberFormatException nfe){
		    	         System.out.println("NumberFormatException: " + nfe.getMessage());
		    	    }
		    	}
		    	else{
		    		done = true;
		    	}		    	
		    }
		}
		catch(Exception e){
			System.out.println("There was an error in receiving or sending data: " + e);
		}
		
		//we are done so close connections
		try{
			incoming.close();
		}
		catch(Exception e){
			System.out.println("Was unable to close, either the connections where cut or connection timed out " + e);
		}
	}
}

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tcp/ip socket server in java

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