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EchoServer.java
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EchoServer.java
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package echo;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.nio.charset.StandardCharsets;
public class EchoServer {
// whether we can handle only one client at a time (single-threaded server)
// or multiple clients (multi-threaded server)
private static boolean ONE_CLIENT_AT_A_TIME = true;
/**
* Listen for a connection from an EchoClient and then echo back each line of its input
* until it disconnects, then wait for another client.
* @param args unused
*/
public static void main(String[] args) {
final int port = 4589;
try ( // try-with-resources: automatically closes the socket declared here
// open the server socket
final ServerSocket serverSocket = new ServerSocket(port);
) {
while (true) {
// get the next client connection
final Socket socket = serverSocket.accept();
if (ONE_CLIENT_AT_A_TIME) {
// handle the client in the main thread
handleClient(socket);
} else {
// handle the client in a new thread, so that the main thread
// can resume waiting for another client
new Thread(new Runnable() {
public void run() {
handleClient(socket);
}
}).start();
}
}
} catch (IOException ioe) {
ioe.printStackTrace();
} // serverSocket is automatically closed here
}
private static void handleClient(final Socket socket) {
try ( // try-with-resources: automatically closes the stream variables declared here
// get an output stream for the client connection,
// and wrap it in a PrintWriter so we can use print()/println() operations
final PrintWriter writeToClient = new PrintWriter(new OutputStreamWriter(socket.getOutputStream(), StandardCharsets.UTF_8));
// get an input stream for the client connection,
// and wrap it into a BufferedReader for the readLine() operation
final BufferedReader readFromClient = new BufferedReader(new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8));
) {
while (true) {
// read a message from the client
final String message = readFromClient.readLine();
if (message == null) break; // client closed its side of the connection
if (message.equals("quit")) break; // client sent a quit message
// prepare a reply, in this case just echoing the message
final String reply = "echo: " + message;
// write the reply to the client
writeToClient.println(reply);
writeToClient.flush(); // important! otherwise the reply may just sit in a buffer, unsent
}
} catch (IOException ioe) {
ioe.printStackTrace();
} // outToClient, inFromClient are automatically closed here by the try-with-resources
try {
socket.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
}