websocket基于java实现在线多人聊天

实现在线多人聊天可以使用Java中的WebSocket协议，以下是一个简单的示例代码：

服务端代码：

import java.io.IOException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.server.ServerEndpoint;

@ServerEndpoint("/chat")
public class ChatServer {
    private static final Set<Session> sessions = Collections.synchronizedSet(new HashSet<Session>());

    @OnOpen
    public void onOpen(Session session) {
        sessions.add(session);
    }

    @OnMessage
    public void onMessage(String message, Session session) throws IOException {
        synchronized (sessions) {
            for (Session s : sessions) {
                s.getBasicRemote().sendText(message);
            }
        }
    }

    @OnClose
    public void onClose(Session session) {
        sessions.remove(session);
    }
}

客户端代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URI;
import java.net.URISyntaxException;

import javax.websocket.ClientEndpoint;
import javax.websocket.CloseReason;
import javax.websocket.ContainerProvider;
import javax.websocket.DeploymentException;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;

@ClientEndpoint
public class ChatClient {
    private static Object waitLock = new Object();

    @OnOpen
    public void onOpen(Session session) {
        System.out.println("Connected to server");
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        System.out.println(message);
    }

    @OnClose
    public void onClose(Session session, CloseReason closeReason) {
        System.out.println(String.format("Session %s close because of %s", session.getId(), closeReason));
        synchronized (waitLock) {
            waitLock.notify();
        }
    }

    public static void main(String[] args) {
        WebSocketContainer container = ContainerProvider.getWebSocketContainer();
        String uri = "ws://localhost:8080/chat";
        try {
            Session session = container.connectToServer(ChatClient.class, new URI(uri));
            BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
            String line = "";
            while (!line.equals("exit")) {
                line = reader.readLine();
                session.getBasicRemote().sendText(line);
            }
            session.close();
        } catch (DeploymentException | URISyntaxException | IOException e) {
            e.printStackTrace();
        }
    }
}

在本地运行服务端（如Tomcat），然后运行客户端即可进行在线多人聊天。注意修改服务端代码中的端口号和路径。