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TCP/IP Client and Server

A simple Client/Server demo program. The server waits for connection and starts a thread when there is a connection request from a client. The server receives a String from the client and returns it to the client in uppercase.

Submitted By: pbl

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Rating:

Views: 6,927

Language: Java

Last Modified: April 28, 2008

Instructions: The client connects to the server specifying "localhost". That means the server and the client are on the same system.
The port 1500 is used for communication.

Snippet

//The server code Server.java:
import java.io.*;
import java.net.*;
/**
* This is to help people to write Client server application
* I tried to make it as simple as possible... the client connect to the server
* the client send a String to the server the server returns it in UPPERCASE thats all
*/
public class Server {
// the socket used by the server
private ServerSocket serverSocket;
// server constructor
Server(int port) {
/* create socket server and wait for connection requests */
try
{
serverSocket = new ServerSocket(port);
System.out.println("Server waiting for client on port " + serverSocket.getLocalPort());
while(true)
{
Socket socket = serverSocket.accept(); // accept connection
System.out.println("New client asked for a connection");
TcpThread t = new TcpThread(socket); // make a thread of it
System.out.println("Starting a thread for a new Client");
t.start();
}
}
catch (IOException e) {
System.out.println("Exception on new ServerSocket: " + e);
}
}
// you must "run" server to have the server run as a console application
public static void main(String[] arg) {
// start server on port 1500
new Server(1500);
}
/** One instance of this thread will run for each client */
class TcpThread extends Thread {
// the socket where to listen/talk
Socket socket;
ObjectInputStream Sinput;
ObjectOutputStream Soutput;
TcpThread(Socket socket) {
this.socket = socket;
}
public void run() {
/* Creating both Data Stream */
System.out.println("Thread trying to create Object Input/Output Streams");
try
{
// create output first
Soutput = new ObjectOutputStream(socket.getOutputStream());
Soutput.flush();
Sinput = new ObjectInputStream(socket.getInputStream());
}
catch (IOException e) {
System.out.println("Exception creating new Input/output Streams: " + e);
return;
}
System.out.println("Thread waiting for a String from the Client");
// read a String (which is an object)
try {
String str = (String) Sinput.readObject();
str = str.toUpperCase();
Soutput.writeObject(str);
Soutput.flush();
}
catch (IOException e) {
System.out.println("Exception reading/writing Streams: " + e);
return;
}
// will surely not happen with a String
catch (ClassNotFoundException o) {
}
finally {
try {
Soutput.close();
Sinput.close();
}
catch (Exception e) {
}
}
}
}
}
//The client code Client.java:
import java.net.*;
import java.io.*;
public class Client {
ObjectInputStream Sinput; // to read the socker
ObjectOutputStream Soutput; // towrite on the socket
Socket socket;
// Constructor connection receiving a socket number
Client(int port) {
// we use "localhost" as host name, the server is on the same machine
// but you can put the "real" server name or IP address
try {
socket = new Socket("localhost", port);
}
catch(Exception e) {
System.out.println("Error connectiong to server:" + e);
return;
}
System.out.println("Connection accepted " +
socket.getInetAddress() + ":" +
socket.getPort());
/* Creating both Data Stream */
try
{
Sinput = new ObjectInputStream(socket.getInputStream());
Soutput = new ObjectOutputStream(socket.getOutputStream());
}
catch (IOException e) {
System.out.println("Exception creating new Input/output Streams: " + e);
return;
}
// now that I have my connection
String test = "aBcDeFgHiJkLmNoPqRsTuVwXyZ";
// send the string to the server
System.out.println("Client sending \"" + test + "\" to serveur");
try {
Soutput.writeObject(test);
Soutput.flush();
}
catch(IOException e) {
System.out.println("Error writting to the socket: " + e);
return;
}
// read back the answer from the server
String response;
try {
response = (String) Sinput.readObject();
System.out.println("Read back from server: " + response);
}
catch(Exception e) {
System.out.println("Problem reading back from server: " + e);
}
try{
Sinput.close();
Soutput.close();
}
catch(Exception e) {}
}
public static void main(String[] arg) {
new Client(1500);
}
}

Copy & Paste

//The server code Server.java:

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

/** 
 * This is to help people to write Client server application 
 *  I tried to make it as simple as possible... the client connect to the server
 *  the client send a String to the server the server returns it in UPPERCASE thats all
 */
public class Server {

// the socket used by the server
	private ServerSocket serverSocket;
	// server constructor
	Server(int port) {
		
		/* create socket server and wait for connection requests */
		try 
		{
			serverSocket = new ServerSocket(port);
			System.out.println("Server waiting for client on port " + serverSocket.getLocalPort());

while(true) 
			{
				Socket socket = serverSocket.accept();  // accept connection
				System.out.println("New client asked for a connection");
				TcpThread t = new TcpThread(socket);    // make a thread of it
				System.out.println("Starting a thread for a new Client");
				t.start();
			}
		}
		catch (IOException e) {
			System.out.println("Exception on new ServerSocket: " + e);
		}
	}

//	you must "run" server to have the server run as a console application
	public static void main(String[] arg) {
		// start server on port 1500
		new Server(1500);
	}
	
	/** One instance of this thread will run for each client */
	class TcpThread extends Thread {
		// the socket where to listen/talk
		Socket socket;
		ObjectInputStream Sinput;
		ObjectOutputStream Soutput;
		
		TcpThread(Socket socket) {
			this.socket = socket;
		}
		public void run() {
			/* Creating both Data Stream */
			System.out.println("Thread trying to create Object Input/Output Streams");
			try
			{
				// create output first
				Soutput = new ObjectOutputStream(socket.getOutputStream());
				Soutput.flush();
				Sinput  = new ObjectInputStream(socket.getInputStream());
			}
			catch (IOException e) {
				System.out.println("Exception creating new Input/output Streams: " + e);
				return;
			}
			System.out.println("Thread waiting for a String from the Client");
			// read a String (which is an object)
			try {
				String str = (String) Sinput.readObject();
				str = str.toUpperCase();
				Soutput.writeObject(str);
				Soutput.flush();
			}
			catch (IOException e) {
				System.out.println("Exception reading/writing  Streams: " + e);
				return;				
			}
			// will surely not happen with a String
			catch (ClassNotFoundException o) {				
			}
			finally {
				try {
					Soutput.close();
					Sinput.close();
				}
				catch (Exception e) {					
				}
			}
		}
	}
}

//The client code Client.java:

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

public class Client {

ObjectInputStream Sinput;		// to read the socker
	ObjectOutputStream Soutput;	// towrite on the socket
	Socket socket;

// Constructor connection receiving a socket number
	Client(int port) {
		// we use "localhost" as host name, the server is on the same machine
		// but you can put the "real" server name or IP address
		try {
			socket = new Socket("localhost", port);
		}
		catch(Exception e) {
			System.out.println("Error connectiong to server:" + e);
			return;
		}
		System.out.println("Connection accepted " +
				socket.getInetAddress() + ":" +
				socket.getPort());

/* Creating both Data Stream */
		try
		{
			Sinput  = new ObjectInputStream(socket.getInputStream());
			Soutput = new ObjectOutputStream(socket.getOutputStream());
		}
		catch (IOException e) {
			System.out.println("Exception creating new Input/output Streams: " + e);
			return;
		}
		// now that I have my connection
		String test = "aBcDeFgHiJkLmNoPqRsTuVwXyZ";
		// send the string to the server
		System.out.println("Client sending \"" + test + "\" to serveur");
		try {
			Soutput.writeObject(test);
			Soutput.flush();
		}
		catch(IOException e) {
			System.out.println("Error writting to the socket: " + e);
			return;
		}
		// read back the answer from the server
		String response;
		try {
			response = (String) Sinput.readObject();
			System.out.println("Read back from server: " + response);
		}
		catch(Exception e) {
			System.out.println("Problem reading back from server: " + e);
		}
		
		try{
			Sinput.close();
			Soutput.close();
		}
		catch(Exception e) {}
	}

public static void main(String[] arg) {
		new Client(1500);
	}
}

Comments
prajayshetty 2008-06-13 12:20:45
thats a nice for learning socketing in java
nuhajat 2008-07-01 12:26:55
Graet!! it`s nice but i`m newbie.. Would u like to help me.. make "Billing Internet Cafe" Aplication please...
kamran_mrz 2009-03-10 16:11:08
hi,it is good but i need a http web browser ,web broser must dont use component and should be simple please help me Zolfaghary@inbox.com
cjdalley 2009-04-24 20:12:25
Perfect example! Thank you very much I've been looking for something like this for weeks!
Rose Smile 2009-05-06 13:44:54
Thank you very much I got a great benifit from it Best regards ..