Server Socket Example

Before we can send client request to a server, we need to make sure that server is running a ServerSocket object and is listening on the same port.

Here is a simple server demo:


package its.day15.sockets;



import java.io.DataInputStream;

import java.io.DataOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.net.ServerSocket;

import java.net.Socket;



public class SimpleServerDemo {

	/**

	 * This is a simple server socket demo

	 * The server socket will start at the assigned port number and will be waiting for requests from clients.

	 * Upon receiving the client request the server will create an internal socket to collaborate with the client socket

	 * The internal socket will open Input and Output streams.

	 * Then the method expects to receive a string from a client and return it back with addition " - from server"

	 * Then the server will close the streams and the internal socket

	 * It will continue waiting for more requests from the clients

	 * 

	 * @param portNumber

	 */

	public void serverSocketService(int portNumber) {

		ServerSocket server = null;

		// register server socket on the portNumber

		try {

			server = new ServerSocket(portNumber);

		} catch (IOException e) {

			System.out.println("Server socket failure: " + e);

			return;

		}

		// start a loop waiting for client requests

		while (true) {

			// make client request, socket and stream objects available for exception cases

			String clientRequest = null;

			Socket socket = null;

			DataOutputStream dos = null;

			DataInputStream dis = null;

			try {

				// listen for a client request and accept the request from a

				// client with creating a local socket

				socket = server.accept();

				// connect input/output streams to the socket

				OutputStream outStream = socket.getOutputStream();

				InputStream inStream = socket.getInputStream();

				// transform into DataInputStream and DataOutputStream to use UTF strings

				dos = new DataOutputStream(outStream);

				dis = new DataInputStream(inStream);				

				// read the client request

				clientRequest = new String(dis.readUTF());

				// mirror this request into the response with a small addition

				dos.writeUTF(clientRequest + " - from server!"); // demo response

				// close the client connection, keep alive the server socket

				socket.close();

			} catch (Exception e) {

				// exception with one client will not stop server from serving other clients

				String response = "ERROR: Server socket failure: " + e + " on the clientRequest="+clientRequest;

				if(dos != null) {

					try {

						dos.writeUTF(response);

						dos.close();

						dis.close();

						socket.close();

					} catch(Exception dosException) {

						System.out.println(dosException);

					}

				}

				System.out.println(response);

			}

		}

	}

	/**

	 * This test will start the server socket on localhost at the portNumber and be waiting for client requests

	 * @param args

	 */

	public static void main(String[] args) {

		SimpleServerDemo server = new SimpleServerDemo();

		server.serverSocketService(5555);

	}

}

Was it clear so far?

Assignments:

1. Open Eclipse and under the package its.day15.sockets in the project week7.network ? create a NEW ? CLASS - SimpleServerDemo.
2. Type the source of this class provided above.
3. Get rid of red lines and do right mouse click on the source - Run ? As Java Application. Now you have server side ready for client requests!
4. Keep this class running and open the source of the ClientSocket.
5. Right mouse click on the source - Run ? As Java Application.
6. Your client sends a request to a server and you should see the response from the server in the Console as: Hello ? from server!
7. The server is still waiting for more requests.
8. Right mouse click on the client source and again - Run ? As Java Application.
9. You will see again the same response from the server.
10. Modify the main() method of the client. Instead of Hello say Prevet (Hello in Russian)
11. Right mouse click on the client source and again - Run ? As Java Application.
12. You will see a new response from the server.
13. Make sure to stop the server program before going to the next session.
14. Eclipse does not provide a simple way to stop a daemon programs. So, just kill Eclipse and start it again.
15. Now modify the serverSocketService method in the SimpleServerDemo class by providing a boolean stopTheProcess in the loop as it is shown below:


	public void serverSocketService(int portNumber) {

		boolean stopTheProcess = false; // THIS IS THE NEW LINE

		ServerSocket server = null;

		// register server socket on the portNumber

		try {

			server = new ServerSocket(portNumber);

		} catch (IOException e) {

			System.out.println("Server socket failure: " + e);

			return;

		}

		// start a loop waiting for client requests

		while (!stopTheProcess) { // THIS IS THE MODIFIED LINE

			// make client request, socket and stream objects available for exception cases

			String clientRequest = null;

			Socket socket = null;

			DataOutputStream dos = null;

			DataInputStream dis = null;

			try {

				// listen for a client request and accept the request from a

				// client with creating a local socket

				socket = server.accept();

				// connect input/output streams to the socket

				OutputStream outStream = socket.getOutputStream();

				InputStream inStream = socket.getInputStream();

				// transform into DataInputStream and DataOutputStream to use UTF strings

				dos = new DataOutputStream(outStream);

				dis = new DataInputStream(inStream);				

				// read the client request

				clientRequest = new String(dis.readUTF());

				// mirror this request into the response with a small addition

				dos.writeUTF(clientRequest + " - from server!"); // demo response

				// close the client connection, keep alive the server socket

				socket.close();

				stopTheProcess = true; // THIS IS THE NEW LINE THAT WILL STOP THE SERVER DAEMON PROCESS

			} catch (Exception e) {

				// exception with one client will not stop server from serving other clients

				String response = "ERROR: Server socket failure: " + e + " on the clientRequest="+clientRequest;

				if(dos != null) {

					try {

						dos.writeUTF(response);

						dos.close();

						dis.close();

						socket.close();

					} catch(Exception dosException) {

						System.out.println(dosException);

					}

				}

				System.out.println(response);

				stopTheProcess = true;

			}

		}

	}

16. Get rid of red lines and do right mouse click on the source - Run ? As Java Application. Now you have server side ready for client requests!
17. Keep this class running and open the source of the ClientSocket.
18. Right mouse click on the source - Run ? As Java Application.
19. Your client sends a request to a server and you should see the response from the server in the Console.
20. The server will stop running after serving one client.
21. Enhance this example with more features in ClientSocket and ServerSocket programs by providing Business Requirements, Design Spec, and implementation Java programs. Compress together in 3.2.3.Sockets.Your.Name.zip and email to dean@ituniversity.us
22. Now you are ready to move to the next section.

package its.day15.sockets; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.net.ServerSocket; import java.net.Socket; public class SimpleServerDemo { /** * This is a simple server socket demo * The server socket will start at the assigned port number and will be waiting for requests from clients. * Upon receiving the client request the server will create an internal socket to collaborate with the client socket * The internal socket will open Input and Output streams. * Then the method expects to receive a string from a client and return it back with addition " - from server" * Then the server will close the streams and the internal socket * It will continue waiting for more requests from the clients * * @param portNumber */ public void serverSocketService(int portNumber) { ServerSocket server = null; // register server socket on the portNumber try { server = new ServerSocket(portNumber); } catch (IOException e) { System.out.println("Server socket failure: " + e); return; } // start a loop waiting for client requests while (true) { // make client request, socket and stream objects available for exception cases String clientRequest = null; Socket socket = null; DataOutputStream dos = null; DataInputStream dis = null; try { // listen for a client request and accept the request from a // client with creating a local socket socket = server.accept(); // connect input/output streams to the socket OutputStream outStream = socket.getOutputStream(); InputStream inStream = socket.getInputStream(); // transform into DataInputStream and DataOutputStream to use UTF strings dos = new DataOutputStream(outStream); dis = new DataInputStream(inStream); // read the client request clientRequest = new String(dis.readUTF()); // mirror this request into the response with a small addition dos.writeUTF(clientRequest + " - from server!"); // demo response // close the client connection, keep alive the server socket socket.close(); } catch (Exception e) { // exception with one client will not stop server from serving other clients String response = "ERROR: Server socket failure: " + e + " on the clientRequest="+clientRequest; if(dos != null) { try { dos.writeUTF(response); dos.close(); dis.close(); socket.close(); } catch(Exception dosException) { System.out.println(dosException); } } System.out.println(response); } } } /** * This test will start the server socket on localhost at the portNumber and be waiting for client requests * @param args */ public static void main(String[] args) { SimpleServerDemo server = new SimpleServerDemo(); server.serverSocketService(5555); } }

public void serverSocketService(int portNumber) { boolean stopTheProcess = false; // THIS IS THE NEW LINE ServerSocket server = null; // register server socket on the portNumber try { server = new ServerSocket(portNumber); } catch (IOException e) { System.out.println("Server socket failure: " + e); return; } // start a loop waiting for client requests while (!stopTheProcess) { // THIS IS THE MODIFIED LINE // make client request, socket and stream objects available for exception cases String clientRequest = null; Socket socket = null; DataOutputStream dos = null; DataInputStream dis = null; try { // listen for a client request and accept the request from a // client with creating a local socket socket = server.accept(); // connect input/output streams to the socket OutputStream outStream = socket.getOutputStream(); InputStream inStream = socket.getInputStream(); // transform into DataInputStream and DataOutputStream to use UTF strings dos = new DataOutputStream(outStream); dis = new DataInputStream(inStream); // read the client request clientRequest = new String(dis.readUTF()); // mirror this request into the response with a small addition dos.writeUTF(clientRequest + " - from server!"); // demo response // close the client connection, keep alive the server socket socket.close(); stopTheProcess = true; // THIS IS THE NEW LINE THAT WILL STOP THE SERVER DAEMON PROCESS } catch (Exception e) { // exception with one client will not stop server from serving other clients String response = "ERROR: Server socket failure: " + e + " on the clientRequest="+clientRequest; if(dos != null) { try { dos.writeUTF(response); dos.close(); dis.close(); socket.close(); } catch(Exception dosException) { System.out.println(dosException); } } System.out.println(response); stopTheProcess = true; } } }