I am working on a program where I have a Server and Client class, but at the moment it only handles only one client at a time. I need the server to be able to handle multiple clients concurrently (simultaneously), using multithreading.
Here is my Server code; how can I change it to handle multiple clients concurrently?
public static void main(String[] args) throws IOException {
ServerSocket socket = new ServerSocket(8945);
Server serverInstance = new Server();
System.out.println("Server is running. Waiting for client.");
while(true) {
server.socket = s.accept();
System.out.println("Client connected");
serverInstance.run();
System.out.println("Client disconnected. Waiting for new client.");
}
}
public void run() {
try {
try {
in = new Scanner(socket.getInputStream());
out = new PrintWriter(socket.getOutputStream());
RequestHandlingMethod();
} finally {
socket.close();
}
} catch (IOException e) {
System.err.println(e);
}
}
Create a separate class that handles the client. Make it implement Runnable
so that you can just start a separate Thread
with it.
public class ClientHandler implements Runnable {
private final Socket socket;
public ClientHandler(Socket socket) {
this.socket = socket;
}
public void run() {
try (Socket socket = this.socket;
Scanner in = new Scanner(socket.getInputStream();
PrintWriter out = new PrintWriter(socket.getOutputStream()) {
//todo: do whatever you need to do
} catch (IOException ex) {
ex.printStackTrace();
}
System.out.println("Client disconnected.");
}
}
Then in your server you do:
System.out.println("Waiting for new client connection");
Socket clientSocket = s.accept();
System.out.println("Client connected");
new Thread(new ClientHandler(clientSocket)).start();
If you don't want to create a lot of disposable Threads, you might want to consider using an ExecutorService
with a cached thread pool (or another thread pool of your choice if you prefer).
You would just create a new ExecutorService
with ExecutorService executor = ExecutorService.newCachedThreadPool()
and then inside your loop you do:
System.out.println("Waiting for new client connection");
Socket clientSocket = s.accept();
System.out.println("Client connected");
executor.submit(new ClientHandler(clientSocket));
If you think you are going to have a lot of concurrent clients, you might want to look at using a non-blocking server with NIO instead. It will have 1 single event loop thread instead (doesn't block on the accept
) and handles all I/O events in there, and you can have a pool of worker threads that do the client handling logic.
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