package examples.example2_one_client_OO;
import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import javax.swing.JOptionPane;
/**
*
* NetworkingExamples project: examples.example2_one_client_OO.
*
* A simple example of networking (Sockets) in which:
* -- A single Server and Client exchange information, one after the other.
*
* This is the Server code.
*
* This is the same example as {@link examples.example1_one_client}
* except structured in a more OO way. In particular, this structure has 3 classes:
* -- Main: for starting the program.
* -- Server: for initiating and running the Server.
* -- Client: for initiating and running the Client.
*
* See {@link examples.example1_one_client#MainForServer} for:
* -- Exactly what information the Server and Client exchange in this demo.
* -- The 7 Key Statements that are all-you-need-to-know to do networking in Java.
*
* See {@link examples.example3_one_client_OO_library} for this same example
* but using the simple networking library in package {@link simpleNetworking}.
*
*
* @author David Mutchler, based on the Java Tutorials on networking. May, 2009.
*/
public class Server implements Runnable {
private Socket socketToCommunicateWithClient;
private BufferedReader in;
private PrintWriter out;
/**
*
* Constructs readers and writers for talking to the Client, as follows:
*
* 1. Constructs a ServerSocket.
*
* 2. Use the ServerSocket to accept a connection from a Client
* (blocks -- i.e. waits -- until a Client offers to connect)
* (a better program would establish a timeout for connecting).
*
* 3. In accepting a connection to the Client, it gets a Socket.
* Use that Socket to:
* a. Get an InputStream. Then decorate the InputStream
* into a BufferedReader (for more efficient communication).
* b. Get an OutputStream. Then decorate the OutputStream
* into a PrintWriter (for convenient ways to write messages).
*
* Finally, this constructor:
* 4. Starts a Thread in which the Server repeatedly communicates with the
* Client (so that you can see a simple example of network communication).
*
*
* @param port Port to use for the ServerSocket
* that accepts a connection to the Client.
* @throws Throwable if any Exception or Error occurs.
*/
public Server(int port) throws Throwable {
try {
//-------------------------------------------------------------------------------------
// KEY #1: Construct a ServerSocket that accepts connections from Clients.
ServerSocket serverSocket = new ServerSocket(port);
//-------------------------------------------------------------------------------------
JOptionPane.showMessageDialog(null,
"The Server has started and will wait for a connection.\n\n"
+ "Start the Client AFTER pressing OK in this dialog.\n\n");
//-------------------------------------------------------------------------------------
// KEY #2: Block (wait) until a Client connects;
// get a Socket for communicating with that Client.
this.socketToCommunicateWithClient = serverSocket.accept();
//-------------------------------------------------------------------------------------
// Done with the ServerSocket, since we wanted to accept only a single Client in this example.
serverSocket.close();
//-------------------------------------------------------------------------------------
// KEY #3: From the Socket, construct a BufferedReader for reading from the Client.
this.in = new BufferedReader(new InputStreamReader(
this.socketToCommunicateWithClient.getInputStream()));
//-------------------------------------------------------------------------------------
//-------------------------------------------------------------------------------------
// KEY #4: From the Socket, construct a PrintWriter for writing to the Client.
this.out = new PrintWriter(
this.socketToCommunicateWithClient.getOutputStream(), true);
//-------------------------------------------------------------------------------------
new Thread(this).start();
} catch (Throwable exception) {
this.close();
throw exception;
}
}
/**
*
* A simple example of communication between this Server and the Client.
*
* It behaves as follows:
*
* Repeatedly, until the Client sends STOP or the user says to stop:
* -- Get a number from the Client.
* -- Display the number from the Client, and get a number from the user.
* -- Add these numbers and send the total to the Client.
*
* The Client can send whatever number it wishes at each iteration;
* in fact, the particular Client in this program takes the number
* that the Server sends it, chooses a random number between 0 and 10,
* and sends the sum back to this Server.
*
* If the user says to stop, the Server sends a STOP message to the Client
* so that the Client will stop too.
*
*/
@Override
public void run() {
try {
//-------------------------------------------------------------------------------------
// Now start communicating with the Client.
//-------------------------------------------------------------------------------------
String dataFromClient, dataFromUser;
int numberFromUser;
JOptionPane.showMessageDialog(null,
"This Server is running on "
+ InetAddress.getLocalHost().getCanonicalHostName() + "\n"
+ "which is IP address "
+ InetAddress.getLocalHost().getHostAddress() + "\n\n");
while (true) {
//-----------------------------------------------------------------------------
// KEY #5: Read from the Client.
dataFromClient = this.in.readLine();
//-----------------------------------------------------------------------------
if (dataFromClient.equals("STOP")) { // Client says to stop.
JOptionPane.showMessageDialog(null,
"Server ended because the Client asked it to do so.\n\n");
break;
}
dataFromUser = JOptionPane.showInputDialog(
"The number from the Client is " + dataFromClient + ".\n\n"
+ "What do you want to add to it?\n\n"
+ "(Or press Cancel to quit this program.)\n\n");
if (dataFromUser == null) { // User selected Cancel in input dialog.
JOptionPane.showMessageDialog(null,
"Server ended because the user asked it to do so.\n\n"
+ "Tell the Client to stop too.\n\n");
this.out.println("STOP"); // Tell the Client to stop
break; // and stop this Server.
}
try {
numberFromUser = Integer.parseInt(dataFromUser);
} catch (NumberFormatException exception) {
JOptionPane.showMessageDialog(null,
"You entered " + dataFromUser + "\n"
+ "which is not a number! I will use 0 instead.\n\n");
numberFromUser = 0;
}
//-----------------------------------------------------------------------------
// KEY #6: Write to the Client.
this.out.println(Integer.parseInt(dataFromClient) + numberFromUser);
//-----------------------------------------------------------------------------
}
} catch (IOException exception) {
System.out.println(exception);
JOptionPane.showMessageDialog(null,
"Server ended, probably because the user closed the Client.\n\n");
} catch (Throwable exception) {
System.out.println(exception);
JOptionPane.showMessageDialog(null, "Server ended abnormally.\n\n");
JOptionPane.showMessageDialog(null, exception.getStackTrace());
}
this.close();
}
/**
* Closes all resources that this Server uses: writer, reader, socket.
*/
void close() {
Closeable[] resourcesToClose = {this.out, this.in};
JOptionPane.showMessageDialog(null, "Closing the Server's resources.");
for (Closeable resource : resourcesToClose) {
try {
resource.close();
} catch (Exception exception) {
// Ignore; we made our best effort at closing the resource.
}
}
try {
this.socketToCommunicateWithClient.close();
} catch (Exception exception) {
// Ignore; we made our best effort at closing the resource.
}
}
}