如何在 Java 中实现基于线程的 UDP 服务器?

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How can I implement a threaded UDP based server in Java ?

Basically what I want, is to connect multiple clients to the server, and let each client have his own thread. The only problem is, that I don't know how to check if a client is trying to connect to the server and spawn a new thread for it.

boolean listening = true; System.out.println("Server started."); while (listening) new ServerThread().start();

In this case the server will spawn new threads until it runs out of memory. Here's the code for the ServerThread ( I think I need here a mechanism that stalls the creation of the ServerThread until a client tries to connect.

public ServerThread(String name) throws IOException { super(name); socket = new DatagramSocket(); }

So fathers of Java programming please help.

解决方案

The design for this to a certain extent depends on whether each complete UDP "dialog" just requires a single request and immediate response, whether it's a single request or response with retransmissions, or whether there'll be a need to process lots of packets for each client.

The RADIUS server I wrote had the single request + retransmit model and spawned a thread for each incoming packet.

As each DatagramPacket was received it was passed to a new thread, and then that thread was responsible for sending back the response. This was because the computation and database accesses involved in generating each response could take a relatively long time and it's easier to spawn a thread than to have some other mechanism to handle new packets that arrive whilst old packets are still being processed.

public class Server implements Runnable { public void run() { while (true) { DatagramPacket packet = socket.receive(); new Thread(new Responder(socket, packet)).start(); } } } public class Responder implements Runnable { Socket socket = null; DatagramPacket packet = null; public Responder(Socket socket, DatagramPacket packet) { this.socket = socket; this.packet = packet; } public void run() { byte[] data = makeResponse(); // code not shown DatagramPacket response = new DatagramPacket(data, data.length, packet.getAddress(), packet.getPort()); socket.send(response); } }