Sample: Java Socket Programming

//The server


import java.io.*;
import java.net.*;
public class Provider{
ServerSocket providerSocket;
Socket connection = null;
ObjectOutputStream out;
ObjectInputStream in;
String message;
Provider(){}
void run()
{
try{
//1. creating a server socket
providerSocket = new ServerSocket(2004, 10);
//2. Wait for connection
System.out.println("Waiting for connection");
connection = providerSocket.accept();
System.out.println("Connection received from " + connection.getInetAddress().getHostName());
//3. get Input and Output streams
out = new ObjectOutputStream(connection.getOutputStream());
out.flush();
in = new ObjectInputStream(connection.getInputStream());
sendMessage("Connection successful");
//4. The two parts communicate via the input and output streams
do{
try{
message = (String)in.readObject();
System.out.println("client>" + message);
if (message.equals("bye"))
sendMessage("bye");
}
catch(ClassNotFoundException classnot){
System.err.println("Data received in unknown format");
}
}while(!message.equals("bye"));
}
catch(IOException ioException){
ioException.printStackTrace();
}
finally{
//4: Closing connection
try{
in.close();
out.close();
providerSocket.close();
}
catch(IOException ioException){
ioException.printStackTrace();
}
}
}
void sendMessage(String msg)
{
try{
out.writeObject(msg);
out.flush();
System.out.println("server>" + msg);
}
catch(IOException ioException){
ioException.printStackTrace();
}
}
public static void main(String args[])
{
Provider server = new Provider();
while(true){
server.run();
}
}
}
  
//The client


import java.io.*;
import java.net.*;
public class Requester{
Socket requestSocket;
ObjectOutputStream out;
  ObjectInputStream in;
  String message;
Requester(){}
void run()
{
try{
//1. creating a socket to connect to the server
requestSocket = new Socket("localhost", 2004);
System.out.println("Connected to localhost in port 2004");
//2. get Input and Output streams
out = new ObjectOutputStream(requestSocket.getOutputStream());
out.flush();
in = new ObjectInputStream(requestSocket.getInputStream());
//3: Communicating with the server
do{
try{
message = (String)in.readObject();
System.out.println("server>" + message);
sendMessage("Hi my server");
message = "bye";
sendMessage(message);
}
catch(ClassNotFoundException classNot){
System.err.println("data received in unknown format");
}
}while(!message.equals("bye"));
}
catch(UnknownHostException unknownHost){
System.err.println("You are trying to connect to an unknown host!");
}
catch(IOException ioException){
ioException.printStackTrace();
}
finally{
//4: Closing connection
try{
in.close();
out.close();
requestSocket.close();
}
catch(IOException ioException){
ioException.printStackTrace();
}
}
}
void sendMessage(String msg)
{
try{
out.writeObject(msg);
out.flush();
System.out.println("client>" + msg);
}
catch(IOException ioException){
ioException.printStackTrace();
}
}
public static void main(String args[])
{
Requester client = new Requester();
client.run();
}
}