Server Socket providing services

Can client ask for a set of specific services?

Yes, this can be easily done if client and server have the following agreements:

a) A client provides a string ? instruction asking for a requested service.
A string-instruction must include a service class name and a string-parameter separated by the "|" character
Example: its.day15.sockets.RequestRepetitionService|Hello

b) It is expected that there is a set of services implemented on the server side.
Each service class must implement the ItsBaseService interface with the run() method.

Here is the ItsBaseService interface:


package its.day15.sockets;

/**

 * The ItsBaseService interface is a blueprint for simple service classes with the run() method

 * @author Jeff.Zhuk@Javaschool.com

 */

public interface ItsBaseService {

	public String run(String params);

}

We provided a very simple implementation of this interface in the RequestRepetitionService class.
The run() method in this class will repeat the request with a small addition.
Of course, more realistic setting would include a set of meaningful services implemented on the server side.


package its.day15.sockets;



public class RequestRepetitionService implements ItsBaseService {



	@Override

	public String run(String params) {

		return params + " - from server!";

	}

	

}

The ServerSocketService source look much more interesting. Read carefully source comments that make code self-explanatory.


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;

/**

 * The ServerSocketService class opens a ServerSocket on a localhost at an assigned port

 * The server socket will be responding to client requests by calling one of existing services

 * All services implement the ItsBaseService interface

 * @author Jeff.Zhuk@Javaschool.com

 *

 */

public class ServerSocketService {

	/**

	 * This is a simple server socket that provide requested services.

	 * 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 socket will create an internal socket to collaborate with the client.

	 * The internal socket will open Input and Output streams.

	 * Then the method expects to receive a string from a client with the instructions on a requested service. 

	 * A string-instruction must include a service class name and a string-parameter separated by the "|" character

	 *  Example: its.day15.sockets.RequestRepetitionService|Hello 

	 * The service class must implement the ItsBaseService interface with the run() method.

	 * The server socket will instantiate the server class and run the service.

	 * The run() method will return a string.

	 * The server socket will send this string back to the client via the Output stream.

	 * 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) {

		boolean stopTheProcess = false;

		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) {

			// 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());

				// process this client request and get a response for a client

				int indexOfSeparator = clientRequest.indexOf("|");

				if(indexOfSeparator < 0) {

					// client request is not valid, it does not have two parts separated by "|"

					dos.writeUTF("ERROR: not a valid request");

					dos.close();

					dis.close();

					socket.close();

					continue;

				}

				String serviceClassName = clientRequest.substring(0, indexOfSeparator);

				String params = clientRequest.substring(indexOfSeparator+1);

				// create an object of he service class that implements

				// ItsBaseService interface

				ItsBaseService service = (ItsBaseService) Class.forName(

						serviceClassName).newInstance();

				// invoke the implemented run() method and get the response

				String response = service.run(params);

				dos.writeUTF(response); // success or failure

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

				socket.close();

				stopTheProcess = true;

			} 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;

			}

		}

	}

	/**

	 * 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) {

		ServerSocketService server = new ServerSocketService();

		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 ? Interface - ItsBaseService.
2. Type the source of this interface provided above.
3. Create a NEW ? Class - RequestRepetitionService.
4. Type the source of this class provided above.
5. Create a NEW ? Class - ServerSocketService.
6. Type the source of this class provided above.
7. Get rid of red lines and do right mouse click on the source - Run ? As Java Application. Now you have server side ready for providing services!
8. Keep this class running and open the source of the ClientSocket.
9. Modify the main() method of the ClientSocket source.
10. Instead of a previous line as a request provide the line its.day15.sockets.RequestRepetitionService|Hello
11. This line includes a full name of the service (with the package name) and the parameter string (Hello).
12. Right mouse click on the modified source - Run ? As Java Application.
13. Your client sends a request to a server and you should see the response from the server in the Console as: Hello ? from server!
14. The server will stop after serving a single client. Right mouse click on the source of ServerSocketService - DEBUG ? As Java Application
15. The server socket will run in the DEBUG mode. Make a breakpoint by double-click on the blue line left from the following line: (see the image below)
String params = clientRequest.substring(indexOfSeparator+1);

16. Modify client parameter again and run again client socket to see the response from the server.
17. Now, the server side will stop at the breakpoint and you can see the value of the serviceClassName variable by moving mouse to this variable.
18. Click F8 to continue the execution of the program or click F6 to execute the program step by step till the end.
19. Modify again the line that client sends to a server. Make any other service name or just remove the package name. This will result to the error on the server side.
20. Check debug variables and the responses in the console.

Debug-ServerSocketService

package its.day15.sockets; /** * The ItsBaseService interface is a blueprint for simple service classes with the run() method * @author Jeff.Zhuk@Javaschool.com */ public interface ItsBaseService { public String run(String params); }

package its.day15.sockets; public class RequestRepetitionService implements ItsBaseService { @Override public String run(String params) { return params + " - from server!"; } }

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; /** * The ServerSocketService class opens a ServerSocket on a localhost at an assigned port * The server socket will be responding to client requests by calling one of existing services * All services implement the ItsBaseService interface * @author Jeff.Zhuk@Javaschool.com * */ public class ServerSocketService { /** * This is a simple server socket that provide requested services. * 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 socket will create an internal socket to collaborate with the client. * The internal socket will open Input and Output streams. * Then the method expects to receive a string from a client with the instructions on a requested service. * A string-instruction must include a service class name and a string-parameter separated by the "|" character * Example: its.day15.sockets.RequestRepetitionService|Hello * The service class must implement the ItsBaseService interface with the run() method. * The server socket will instantiate the server class and run the service. * The run() method will return a string. * The server socket will send this string back to the client via the Output stream. * 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) { boolean stopTheProcess = false; 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) { // 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()); // process this client request and get a response for a client int indexOfSeparator = clientRequest.indexOf("|"); if(indexOfSeparator < 0) { // client request is not valid, it does not have two parts separated by "|" dos.writeUTF("ERROR: not a valid request"); dos.close(); dis.close(); socket.close(); continue; } String serviceClassName = clientRequest.substring(0, indexOfSeparator); String params = clientRequest.substring(indexOfSeparator+1); // create an object of he service class that implements // ItsBaseService interface ItsBaseService service = (ItsBaseService) Class.forName( serviceClassName).newInstance(); // invoke the implemented run() method and get the response String response = service.run(params); dos.writeUTF(response); // success or failure // close the client connection, keep alive the server socket socket.close(); stopTheProcess = true; } 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; } } } /** * 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) { ServerSocketService server = new ServerSocketService(); server.serverSocketService(5555); } }