Java WebSocket

WebSocket是基于HTTP升级的全双工通信协议，适用于实时推送场景。

WebSocket特点

WebSocket vs HTTP

协议握手流程

客户端                              服务端
   |                                  |
   |── HTTP请求（Upgrade）──────────→|
   |  GET /chat HTTP/1.1              |
   |  Upgrade: websocket              |
   |  Connection: Upgrade             |
   |  Sec-WebSocket-Key: xxx          |
   |                                  |
   |←── HTTP响应（101 Switching）────|
   |  HTTP/1.1 101 Switching Protocols|
   |  Upgrade: websocket              |
   |  Sec-WebSocket-Accept: xxx       |
   |                                  |
   ========== WebSocket连接建立 ==========
   |                                  |
   |←────── 数据帧 ───────────────────|  双向通信
   |────── 数据帧 ──────────────────→|

Java WebSocket服务端（JSR-356）

注解方式

@ServerEndpoint("/chat")
public class ChatEndpoint {

    private Session session;

    @OnOpen
    public void onOpen(Session session) {
        this.session = session;
        System.out.println("连接打开: " + session.getId());
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        System.out.println("收到消息: " + message);
        // 回送消息
        session.getAsyncRemote().sendText("Echo: " + message);
    }

    @OnClose
    public void onClose(Session session, CloseReason reason) {
        System.out.println("连接关闭: " + reason.getReasonPhrase());
    }

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

    // 发送消息到所有客户端
    public static void broadcast(String message) {
        for (Session session : sessionSet) {
            session.getAsyncRemote().sendText(message);
        }
    }
}

配置发布

public class WebSocketServer {
    public static void main(String[] args) throws Exception {
        Server server = new Server("localhost", 8080, "/ws", ChatEndpoint.class);
        server.start();
        System.out.println("WebSocket服务端启动: ws://localhost:8080/ws/chat");
    }
}

Java WebSocket客户端

注解方式

@ClientEndpoint
public class ChatClient {

    private Session session;

    @OnOpen
    public void onOpen(Session session) {
        this.session = session;
        System.out.println("已连接服务端");
    }

    @OnMessage
    public void onMessage(String message) {
        System.out.println("收到: " + message);
    }

    @OnClose
    public void onClose(Session session, CloseReason reason) {
        System.out.println("连接关闭");
    }

    public void send(String message) {
        session.getAsyncRemote().sendText(message);
    }

    public static void main(String[] args) throws Exception {
        WebSocketContainer container = ContainerProvider.getWebSocketContainer();
        ChatClient client = new ChatClient();

        Session session = container.connectToServer(client,
            URI.create("ws://localhost:8080/ws/chat"));

        // 发送消息
        client.send("Hello WebSocket");

        Thread.sleep(5000);
        session.close();
    }
}

Session常用方法

Session session = ...;

// 基本信息
String id = session.getId();
URI uri = session.getRequestURI();
boolean open = session.isOpen();

// 发送消息
session.getBasicRemote().sendText("文本消息");      // 同步发送
session.getAsyncRemote().sendText("文本消息");       // 异步发送
session.getBasicRemote().sendBinary(ByteBuffer.wrap(bytes));  // 二进制

// 发送对象（需配置编码器）
session.getBasicRemote().sendObject(userObject);

// 关闭连接
session.close(new CloseReason(CloseReason.CloseCodes.NORMAL_CLOSURE, "正常关闭"));

// 用户属性
session.getUserProperties().put("username", "张三");
String username = (String) session.getUserProperties().get("username");

// 最大空闲超时
session.setMaxIdleTimeout(30000);  // 30秒无活动则关闭

// 最大消息大小
session.setMaxBinaryMessageBufferSize(64 * 1024);
session.setMaxTextMessageBufferSize(64 * 1024);

Spring Boot WebSocket

配置

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {

    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(new ChatHandler(), "/chat")
                 .setAllowedOrigins("*");
    }
}

Handler实现

public class ChatHandler extends TextWebSocketHandler {

    private final List<WebSocketSession> sessions = new CopyOnWriteArrayList<>();

    @Override
    public void afterConnectionEstablished(WebSocketSession session) {
        sessions.add(session);
        System.out.println("新连接: " + session.getId());
    }

    @Override
    protected void handleTextMessage(WebSocketSession session, TextMessage message) {
        String payload = message.getPayload();
        System.out.println("收到: " + payload);

        // 广播给所有客户端
        for (WebSocketSession s : sessions) {
            if (s.isOpen()) {
                s.sendMessage(new TextMessage(payload));
            }
        }
    }

    @Override
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) {
        sessions.remove(session);
        System.out.println("连接关闭: " + session.getId());
    }

    @Override
    public void handleTransportError(WebSocketSession session, Throwable exception) {
        System.out.println("传输错误: " + exception.getMessage());
    }
}

适用场景

注意事项

WebSocket基于HTTP升级，握手阶段使用HTTP

wss:// 是安全WebSocket，类似HTTPS

连断后需实现重连机制

大量连接时注意资源管理

心跳机制检测连接状态

要点总结

1. WebSocket全双工通信，一次握手持久连接
2. 通过HTTP Upgrade升级建立连接
3. Java使用 @ServerEndpoint/@ClientEndpoint 注解开发
4. Session 提供发送消息和管理连接的方法
5. 适用于聊天、监控、游戏等实时场景