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Java 连接 WebSocket 入门教程

news 2025/7/18 12:43:38

Java 连接 WebSocket 入门教程

1. WebSocket 简介

WebSocket 是一种全双工通信协议，它允许客户端和服务器之间建立持久连接，实现低延迟、实时交互。相比于传统的 HTTP 轮询，WebSocket 具有更高的效率和更低的带宽消耗。

2. Java WebSocket 依赖

在 Java 中，我们可以使用 javax.websocket 或 Spring WebSocket 来实现 WebSocket 连接。

2.1 添加 Maven 依赖

对于 Java EE WebSocket：

<dependency>
    <groupId>javax.websocket</groupId>
    <artifactId>javax.websocket-api</artifactId>
    <version>1.1</version>
</dependency>

对于 Spring WebSocket：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-websocket</artifactId>
</dependency>

3. Java WebSocket 服务器端实现

3.1 使用 Java EE 实现 WebSocket 服务器

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

@ServerEndpoint("/websocket")
public class WebSocketServer {
    private static final CopyOnWriteArraySet<Session> sessions = new CopyOnWriteArraySet<>();
    
    @OnOpen
    public void onOpen(Session session) {
        sessions.add(session);
        System.out.println("新连接建立: " + session.getId());
    }
    
    @OnMessage
    public void onMessage(String message, Session session) throws IOException {
        System.out.println("收到消息: " + message);
        for (Session s : sessions) {
            s.getBasicRemote().sendText("服务器响应: " + message);
        }
    }
    
    @OnClose
    public void onClose(Session session) {
        sessions.remove(session);
        System.out.println("连接关闭: " + session.getId());
    }
    
    @OnError
    public void onError(Session session, Throwable error) {
        error.printStackTrace();
    }
}

3.2 配置 WebSocket 服务器

如果使用的是 Spring Boot，需要创建 WebSocket 配置类：

import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.config.annotation.EnableWebSocket;
import org.springframework.web.socket.config.annotation.WebSocketConfigurer;
import org.springframework.web.socket.config.annotation.WebSocketHandlerRegistry;

@Configuration
@EnableWebSocket
public class WebSocketConfig implements WebSocketConfigurer {
    @Override
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
        registry.addHandler(new MyWebSocketHandler(), "/ws").setAllowedOrigins("*");
    }
}

4. Java WebSocket 客户端实现

使用 java.net.http.WebSocket 进行客户端连接：

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.WebSocket;
import java.util.concurrent.CompletionStage;

public class WebSocketClient {
    public static void main(String[] args) {
        HttpClient client = HttpClient.newHttpClient();
        WebSocket webSocket = client.newWebSocketBuilder()
            .buildAsync(URI.create("ws://localhost:8080/websocket"), new WebSocketListener())
            .join();
        webSocket.sendText("Hello WebSocket!", true);
    }
}

class WebSocketListener implements WebSocket.Listener {
    @Override
    public void onOpen(WebSocket webSocket) {
        System.out.println("WebSocket 连接成功");
        webSocket.request(1);
    }

    @Override
    public CompletionStage<?> onText(WebSocket webSocket, CharSequence data, boolean last) {
        System.out.println("收到消息: " + data);
        webSocket.request(1);
        return null;
    }
}