Whats
a socket?
Every computer
on a network has an IP address. This address is like
your house address, something that identifies your computer uniquely, allowing others to communicate
with your computer. I wont go much into IP
addresses, but let me just tell you
that an IP
address looks something like this -
64.104.137.158 a set of numbers separated
with dots.
However, some computers with rich owners will also choose
to have a domain name in addition to this sick looking number, so that people can easily identify them.
A domain name looks
far more sane - like www.yahoo.com.There
are some special computer on the
Internet, whose sole purpose in life is to translate the domain name to IP address and vice versa.
An
IP address = uniquely identifies a computer on the network.
A
port number = uniquely identifies a program running on a computer.
An
IP address + A port number = SOCKET
a socket is a combination of an IP address and a port. A
socket address lets other computers on the network locate a certain program running on a certain
computer. You may represent a socket address like 64.104.137.58:80, where 64.104.137.58 is the IP address and 80
is the port number.
Setps For Program
1: One Java program will try to connect to another Java
program.
Lets call the first program
as Client,
and the second
as Server.
2: Once connected, the client program is going to accept whatever you type, and send it
dutifully to the
server program.
3: The server is going to send back the same text to the client, just to show that it is least
interested in
doing such an uninteresting thing.
Create 2 fresh Java programs and call them Server.java and Client.java.
Server.java
import java.net.*;
import java.io.*;
public class Server
{
public static void main(String[] ar)
{
int port = 6666; // just a random port.
try
{
ServerSocket ss = new ServerSocket(port); // create a server socket and bind
System.out.println("Waiting for a client...");
Socket socket = ss.accept(); // make the server listen for a connection
System.out.println("Client Recived.");
System.out.println(); /* Get the input and output streams of the socket, so that you can receive and send data to the client.*/
InputStream sin = socket.getInputStream();
OutputStream sout = socket.getOutputStream(); /*Just converting them to different streams, so that string handling becomes easier.*/
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
String line = null;
while(true)
{
line = in.readUTF(); // wait for the client to send a line of text.
System.out.println("Data from Client: " + line);
System.out.println("I'm sending it back...");
out.writeUTF(line); // send the same line back to the client.
out.flush(); //flush the stream .
System.out.println("Waiting for the next line...");
System.out.println();
}
}
catch(Exception x)
{
x.printStackTrace();
}
}
}
Client.java
import java.net.*;
import java.io.*;
public class Client
{
public static void main(String[] ar)
{
int serverPort = 6666; // make sure you give the port number on which the server is listening.
String address = "127.0.0.1"; // this is the IP address of the server program's computer.
try
{
InetAddress ipAddress = InetAddress.getByName(address); // create an object that represents the above IP address.
System.out.println("a socket with IP address " + address + " and port " + serverPort + "?");
Socket socket = new Socket(ipAddress, serverPort); // create a socket with the server's IP address and server's port.
System.out.println("----Connect-----");
/* Get the input and output streams of the socket, so that you can receive and send data to the client*/
InputStream sin = socket.getInputStream();
OutputStream sout = socket.getOutputStream();
// Just converting them to different streams, so that string handling becomes easier.
DataInputStream in = new DataInputStream(sin);
DataOutputStream out = new DataOutputStream(sout);
// Create a stream to read from the keyboard.
BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
String line = null;
System.out.println("Type in something and press enter. ");
System.out.println();
while(true)
{
line = keyboard.readLine(); // wait for the user to type in something and press enter.
System.out.println("Sending this line to the server...");
out.writeUTF(line); // send the above line to the server.
out.flush(); // flush the stream to ensure that the data reaches the other end.
line = in.readUTF(); // wait for the server to send a line of text.
System.out.println("The server was very polite. It sent me this : " + line);
System.out.println("Looks like the server is pleased with us. Go ahead and enter more lines.");
System.out.println();
}
} catch(Exception x) {
x.printStackTrace();
}
}
}
Compile it with
javac Server.java Client.java
Open two command windows (DOS prompts). In one of those, enter
java Server
and in the other,
java Client
