websocket 实现后端主动前端推送数据、及时通讯(vue3 + springboot)

实现WebSocket后端主动向前端推送数据以及即时通讯，可以使用Vue 3作为前端框架，Spring Boot作为后端框架。以下是一个基本的实现步骤和示例代码。

后端（Spring Boot）

添加依赖：
在Spring Boot项目的pom.xml中添加WebSocket相关的依赖。

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

配置WebSocket：
创建一个配置类来注册WebSocket端点。

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 {  

    private final MyWebSocketHandler webSocketHandler;  

    public WebSocketConfig(MyWebSocketHandler webSocketHandler) {  
        this.webSocketHandler = webSocketHandler;  
    }  

    @Override  
    public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {  
        registry.addHandler(webSocketHandler, "/ws").setAllowedOrigins("*");  
    }  
}

创建WebSocket处理器：
处理WebSocket连接、消息和错误。

import org.springframework.stereotype.Component;  
import org.springframework.web.socket.*;  
import org.springframework.web.socket.handler.TextWebSocketHandler;  

import java.util.concurrent.CopyOnWriteArraySet;  

@Component  
public class MyWebSocketHandler extends TextWebSocketHandler {  

    private final CopyOnWriteArraySet<WebSocketSession> sessions = new CopyOnWriteArraySet<>();  

    @Override  
    public void afterConnectionEstablished(WebSocketSession session) throws Exception {  
        sessions.add(session);  
        System.out.println("New connection established: " + session.getId());  
    }  

    @Override  
    protected void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {  
        // 处理来自客户端的消息  
        System.out.println("Received message: " + message.getPayload());  
    }  

    @Override  
    public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {  
        sessions.remove(session);  
        System.out.println("Connection closed: " + session.getId());  
    }  

    @Override  
    public void handleTransportError(WebSocketSession session, Throwable exception) throws Exception {  
        System.err.println("Transport error: " + exception.getMessage());  
    }  

    public void sendMessageToAll(String message) {  
        for (WebSocketSession session : sessions) {  
            if (session.isOpen()) {  
                try {  
                    session.sendMessage(new TextMessage(message));  
                } catch (Exception e) {  
                    e.printStackTrace();  
                }  
            }  
        }  
    }  
}

在控制器中使用WebSocket处理器：
你可以通过注入MyWebSocketHandler来在其他地方（如控制器）发送消息。

import org.springframework.beans.factory.annotation.Autowired;  
import org.springframework.web.bind.annotation.GetMapping;  
import org.springframework.web.bind.annotation.RequestParam;  
import org.springframework.web.bind.annotation.RestController;  

@RestController  
public class WebSocketController {  

    private final MyWebSocketHandler webSocketHandler;  

    @Autowired  
    public WebSocketController(MyWebSocketHandler webSocketHandler) {  
        this.webSocketHandler = webSocketHandler;  
    }  

    @GetMapping("/send")  
    public String sendMessage(@RequestParam String message) {  
        webSocketHandler.sendMessageToAll(message);  
        return "Message sent!";  
    }  
}

前端（Vue 3）

安装WebSocket库（可选）：
虽然Vue 3本身不需要额外的库来使用WebSocket，但你可以使用如reconnecting-websocket这样的库来处理重连等复杂情况。

创建WebSocket连接：
在Vue组件中创建WebSocket连接，并处理消息和连接事件。

<template>  
  <div>  
    <h1>WebSocket Demo</h1>  
    <ul>  
      <li v-for="message in messages" :key="message">{{ message }}</li>  
    </ul>  
  </div>  
</template>  

<script>  
export default {  
  data() {  
    return {  
      socket: null,  
      messages: []  
    };  
  },  
  mounted() {  
    this.connectWebSocket();  
  },  
  methods: {  
    connectWebSocket() {  
      this.socket = new WebSocket('ws://localhost:8080/ws');  

      this.socket.onopen = () => {  
        console.log('WebSocket connection opened');  
      };  

      this.socket.onmessage = (event) => {  
        this.messages.push(event.data);  
      };  

      this.socket.onclose = () => {  
        console.log('WebSocket connection closed');  
        // Optionally, try to reconnect here  
      };  

      this.socket.onerror = (error) => {  
        console.error('WebSocket error:', error);  
      };  
    }  
  },  
  beforeUnmount() {  
    if (this.socket) {  
      this.socket.close();  
    }  
  }  
};  
</script>  

<style scoped>  
/* Add your styles here */  
</style>

发送消息（可选）：
你可以添加一个表单来发送消息到后端，后端再通过WebSocket广播给所有连接的客户端。

<!-- 在模板中添加表单 -->  
<template>  
  <div>  
    <h1>WebSocket Demo</h1>  
    <form @submit.prevent="sendMessage">  
      <input v-model="newMessage" placeholder="Type a message" />  
      <button type="submit">Send</button>  
    </form>  
    <ul>  
      <li v-for="message in messages" :key="message">{{ message }}</li>  
    </ul>  
  </div>  
</template>  

<script>  
export default {  
  data() {  
    return {  
      socket: null,  
      messages: [],  
      newMessage: ''  
    };  
  },  
  mounted() {  
    this.connectWebSocket();  
  },  
  methods: {  
    connectWebSocket() {  
      // ...（与之前相同）  
    },  
    sendMessage() {  
      if (this.socket && this.socket.readyState === WebSocket.OPEN) {  
        this.socket.send(this.newMessage);  
        this.newMessage = ''; // Clear the input field  
      } else {  
        console.error('WebSocket is not open');  
      }  
    }  
  },  
  beforeUnmount() {  
    // ...（与之前相同）  
  }  
};  
</script>