Simulate Multiple clients with different IPs to server socket

I have a server socket application which accepts multiple client. I want to write client application in java which send request to server application. Is there any way I can simulate multiple clients with different IPs to the server application

Thanks,
Vinodhini.

Please check if following approach help you?

I have verified the solution on Linux within same machine.

my Linux machine have only one NIC(Network Interface Card).

/sbin/ifconfig

eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
          inet addr:10.x.x.x  Bcast:x.x.x.x  Mask:255.255.x.xx

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.x.x.x

I have temporarily added multiple IP addresses to this NIC

You can use the 'ifconfig' command to add an IP address to a NIC. But, please note that this IP address will not be available after rebooting the machine. Here, we assume that you already have a NIC with a static IP configured in it. If we need to add two more IP addresses, say 192.168.1.25 and 192.168.1.26 to this interface, we can accomplish this by executing the following commands as root user:

ifconfig eth0:1 192.168.1.25 netmask 255.255.255.0
ifconfig eth0:2 192.168.1.26 netmask 255.255.255.0

Post addition:

/sbin/ifconfig

eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
          inet addr:10.x.x.x  Bcast:x.x.x.x  Mask:255.255.x.xx

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.x.x.x
		  
eth0:1    Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
          inet addr:192.168.1.25  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

eth0:2    Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
          inet addr:192.168.1.27  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

Now my Linux host has 2 extra temporary IP Address.

I am running following Server Socket program on my Linux machine

RemoteFileServer.java

package socket.learning;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.BindException;
import java.net.ServerSocket;
import java.net.Socket;

public class RemoteFileServer {
	public static void main(String[] args) {
		RemoteFileServer server = new RemoteFileServer();
		server.acceptConnections(Integer.parseInt(args[0]));
	}

	public void acceptConnections(int listenPort) {
		try {
			ServerSocket server = new ServerSocket(listenPort);
			Socket incomingConnection = null;
			while (true) {
				incomingConnection = server.accept();
				handleConnection(incomingConnection);
			}
		} catch (BindException e) {
			System.out.println("Unable to bind to port " + listenPort);
		} catch (IOException e) {
			System.out.println("Unable to instantiate a ServerSocket on port: "
					+ listenPort);
		}
	}

	public void handleConnection(Socket incomingConnection) {
		try {
			System.out.println("Client socket details:  getInetAddress  "
					+ incomingConnection.getInetAddress()
					+ "    getLocalAddress  "
					+ incomingConnection.getLocalAddress()
					+ "   getRemoteSocketAddress  "
					+ incomingConnection.getRemoteSocketAddress());
			OutputStream outputToSocket = incomingConnection.getOutputStream();

			InputStream inputFromSocket = incomingConnection.getInputStream();
			BufferedReader streamReader = new BufferedReader(
					new InputStreamReader(inputFromSocket));
			String fileName = streamReader.readLine();
			FileReader fileReader = new FileReader(new File(fileName));
			BufferedReader bufferedFileReader = new BufferedReader(fileReader);
			PrintWriter streamWriter = new PrintWriter(outputToSocket);
			String line = null;
			while ((line = bufferedFileReader.readLine()) != null) {
				streamWriter.println(line);
			}
			fileReader.close();
			streamWriter.close();
			streamReader.close();
		} catch (Exception e) {
			System.out.println("Error handling a client: " + e);
		}
	}
}

Execution:

java -cp .  socket/learning/RemoteFileServer 9999

9999 is Server socket bind/listen port.

Running following Client Socket program on my Linux machine

To bind client socket to a local address using following Socket constructor

public Socket(InetAddress address,
      int port,
      InetAddress localAddr,
      int localPort)
       throws IOException
Creates a socket and connects it to the specified remote address on the specified remote port. The Socket will also bind() to the local address and port supplied.
If the specified local address is null it is the equivalent of specifying the address as the AnyLocal address (see InetAddress.isAnyLocalAddress()).

A local port number of zero will let the system pick up a free port in the bind operation.

If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException.

Parameters:
address - the remote address
port - the remote port
localAddr - the local address the socket is bound to, or null for the anyLocal address.
localPort - the local port the socket is bound to or zero for a system selected free port.

RemoteFileClient.java

package socket.learning;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

public class RemoteFileClient {
	protected String hostIP;
	protected int hostPort;
	protected BufferedReader socketReader;
	protected PrintWriter socketWriter;

	public RemoteFileClient(String hostIP, int hostPort) {
		this.hostIP = hostIP;
		this.hostPort = hostPort;
	}

	public static void main(String[] args) {
		RemoteFileClient remoteFileClient = new RemoteFileClient(args[0],
				Integer.parseInt(args[1]));
		remoteFileClient.setUpConnection(args[3]);
		String fileContents = remoteFileClient.getFile(args[2]);
		remoteFileClient.tearDownConnection();
		System.out.println(fileContents);
	}

	public void setUpConnection(String clientIpAddress) {
		try {
			Socket client = new Socket(hostIP, hostPort,
					InetAddress.getByName(clientIpAddress), 0);
			socketReader = new BufferedReader(new InputStreamReader(
					client.getInputStream()));
			socketWriter = new PrintWriter(client.getOutputStream());
		} catch (UnknownHostException e) {
			System.out
			.println("Error setting up socket connection: unknown host at "
					+ hostIP);
		} catch (IOException e) {
			e.printStackTrace();
			System.out.println("Error setting up socket connection: " + e);
		}
	}

	public String getFile(String fileNameToGet) {
		StringBuffer fileLines = new StringBuffer();
		try {
			socketWriter.println(fileNameToGet);
			socketWriter.flush();
			String line = null;
			while ((line = socketReader.readLine()) != null)
				fileLines.append(line + "\n");
		} catch (IOException e) {
			System.out.println("Error reading from file: " + fileNameToGet);
		}
		return fileLines.toString();
	}

	public void tearDownConnection() {
		try {
			socketWriter.close();
			socketReader.close();
		} catch (IOException e) {
			System.out.println("Error tearing down socket connection: " + e);
		}
	}
}

Execution:

java -cp .  socket/learning/RemoteFileClient 10.x.x.x 9999 /tmp/test.log 192.168.1.27
java -cp .  socket/learning/RemoteFileClient 10.x.x.x 9999 /tmp/test.log 192.168.1.25
java -cp .  socket/learning/RemoteFileClient 10.x.x.x 9999 /tmp/test.log 10.x.x.x
java -cp .  socket/learning/RemoteFileClient 10.x.x.x 9999 /tmp/test.log 127.0.0.1

Corresponding Server console output:

Client socket details:  getInetAddress  /192.168.1.27    getLocalAddress  /10.x.x.x   getRemoteSocketAddress  /192.168.1.27:14774
Client socket details:  getInetAddress  /192.168.1.25    getLocalAddress  /10.x.x.x   getRemoteSocketAddress  /192.168.1.25:29188
Client socket details:  getInetAddress  /10.x.x.x    getLocalAddress  /10.x.x.x   getRemoteSocketAddress  /10.x.x.x:42407
Client socket details:  getInetAddress  /127.0.0.1    getLocalAddress  /10.x.x.x   getRemoteSocketAddress  /127.0.0.1:36002