Java WebSocket实现简易聊天室

Java WebSocket可以用于实现简易聊天室。下面是一个简单的示例代码：

1. 首先，创建一个WebSocketServer类，继承自javax.websocket.Endpoint，实现onOpen、onMessage、onClose和onError方法。

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.CopyOnWriteArraySet;

@ServerEndpoint("/chatRoom")
public class WebSocketServer {

    //在线人数
    private static int onlineCount = 0;

    //存储每个客户端对应的WebSocketServer对象
    private static CopyOnWriteArraySet<WebSocketServer> webSocketSet = new CopyOnWriteArraySet<>();

    //与某个客户端的会话，需要通过它来给客户端发送数据
    private Session session;

    @OnOpen
    public void onOpen(Session session) {
        this.session = session;
        //将WebSocketServer对象加入到webSocketSet中
        webSocketSet.add(this);
        //在线人数加1
        addOnlineCount();
        System.out.println("有新连接加入！当前在线人数为" + getOnlineCount());
    }

    @OnClose
    public void onClose() {
        //将WebSocketServer对象从webSocketSet中移除
        webSocketSet.remove(this);
        //在线人数减1
        subOnlineCount();
        System.out.println("有一连接关闭！当前在线人数为" + getOnlineCount());
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        System.out.println("来自客户端的消息：" + message);
        //群发消息
        for (WebSocketServer webSocketServer : webSocketSet) {
            try {
                webSocketServer.sendMessage(message);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    @OnError
    public void onError(Session session, Throwable error) {
        System.out.println("发生错误：" + error.getMessage());
        error.printStackTrace();
    }

    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }

    public static synchronized int getOnlineCount() {
        return onlineCount;
    }

    public static synchronized void addOnlineCount() {
        WebSocketServer.onlineCount++;
    }

    public static synchronized void subOnlineCount() {
        WebSocketServer.onlineCount--;
    }
}

2. 在web.xml中配置WebSocketServlet。

<servlet>
    <servlet-name>WebSocketServlet</servlet-name>
    <servlet-class>org.apache.tomcat.websocket.server.WsSci</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

3. 在jsp页面中添加WebSocket连接。

var websocket = new WebSocket("ws://" + window.location.host + "/chatRoom");
websocket.onopen = function () {
    console.log("WebSocket连接成功！");
};
websocket.onmessage = function (event) {
    console.log("接收到服务器发送的消息：" + event.data);
};
websocket.onclose = function () {
    console.log("WebSocket连接关闭！");
};
websocket.onerror = function () {
    console.log("WebSocket连接发生错误！");
};

4. 发送消息。

<button onclick="send()">发送</button>

<script>
    function send() {
        var message = document.getElementById("message").value;
        websocket.send(message);
    }
</script>

这样，一个简易聊天室就实现了。多个用户可以在同一页面中实时聊天。