Java Network Programming (Socket Programming in Java)

JAVA NETWORK

Network programming is used to execute programs across multiple machines that are connected by a network.

The java.net package contains a collection of classes and interfaces that provide this functionality.

The java.net package provides support for the two common network protocols:

• TCP - TCP (Transmission Control Protocol) is for reliable communication between two applications. It is used over the Internet protocol, known as TCP/IP.
• UDP - (User Datagram Protocol) is a connectionless protocol that is used to transmit data packets between applications.

The socket provides the way to communicate between two computers using TCP. The client creates a socket on its end and support for the two common network protocols:

• TCP - TCP (Transmission Control Protocol) is for reliable communication between two applications. It is used over the Internet protocol, known as TCP/IP.
• UDP - (User Datagram Protocol) is a connectionless protocol that is used to transmit data packets between applications to connect that socket to a server.

There are two types of TCP socket present in Java: server and clients.

The server socket class acts as a listener which waits for clients to connect.

The client's socket class is for clients. It initiates the exchange protocol and connects to the server.

The creation of socket object implicitly establishes a connection between the client and server.

Constructors client sockets

Socket(String hostName, int port) throws UnknownHostException, IOException	It creates a socket connected to the named host and port.
Socket(InetAddress ipAddress, int port) throws IOException	It creates a socket using a preexisting InetAddress object and a port.

Useful Methods

Modifier and Type	Method	Description
InetAddress	getInetAddress( )	It returns the InetAddress associated with the Socket object. It returns null if the socket is not connected.
int	getPort( )	It returns the remote port to which the invoking Socket object is connected. It returns 0 if the socket is not connected.
int	getLocalPort( )	It returns the local port to which the invoking Socket object is bound. It returns –1 if the socket is not bound.

Modifier and Type	Method	Description
InputStream	getInputStream( ) throws IOException	It returns the InputStream associated with the invoking socket.
OutputStream	GetOutputStream( ) throws IOException	It returns the OutputStream associated with the invoking socket.

We can gain access to the input and output streams associated with a Socket by using getInputStream( ) and getOuptutStream( ) methods. These methods can throw an IOException if the socket has been invalidated by a lost connection.

Java Socket Programming Example

This is the client class.

import java.io.DataOutputStream;
import java.net.Socket;
public class MyClient {
public static void main(String[] args) {
try {
Socket s = new Socket("localhost", 6061);
DataOutputStream dout = new DataOutputStream(s.getOutputStream());
dout.writeUTF("Connected to server");
dout.flush();
dout.close();
s.close();
} catch (Exception e) {
System.out.println(e);
}
}
}

This is a server class.

import java.io.DataInputStream;
import java.net.ServerSocket;
import java.net.Socket;
public class MyServer {
public static void main(String[] args) {
try {
ServerSocket ss = new ServerSocket(6061);
Socket s = ss.accept();// establishes connection
DataInputStream dis = new DataInputStream(s.getInputStream());
String str = (String) dis.readUTF();
System.out.println("message = " + str);
ss.close();
} catch (Exception e) {
System.out.println(e);
}
}
}

Output:

message = Connected to server