java，springboot实现websocket消息推送

加入依赖

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

新建一个WebSocketConfig.java文件

package com.example.demo.config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;
@Configuration
public class WebSocketConfig {
    @Bean
    public ServerEndpointExporter serverEndpointExporter(){
        return new ServerEndpointExporter();
    }
}

新建一个 WebSocketController.java文件

package com.example.demo.controller;
import org.springframework.stereotype.Component;
import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.CopyOnWriteArraySet;
@ServerEndpoint("/websocket")
@Component
public class WebsocketController {
    private static int onlineCount = 0;
    private static CopyOnWriteArraySet<WebsocketController> webSocketSet = new CopyOnWriteArraySet<WebsocketController>();
    private Session session;
    /**
     * 成功建立连接调用
     */
    @OnOpen
    public void onOpen(Session session){
        this.session = session;
        webSocketSet.add(this);     
        addOnlineCount();           
        System.out.println("有用户加入直播间，当前在线人数为" + getOnlineCount());
    }
    /**
     * 连接关闭调用的方法
     */
    @OnClose
    public void onClose(){
        webSocketSet.remove(this);  //删除连接
        subOnlineCount();           //在线人数减1
        System.out.println("有人退出直播，当前在线人数为" + getOnlineCount());
    }
    /**
     * 收到客户端消息后调用的方法
     */
    @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(WebsocketTest item: webSocketSet){
            try {
                item.sendMessage(message);
            } catch (IOException e) {
                e.printStackTrace();
                continue;
            }
        }
    }
    /**
     * 发生错误时调用
     */
    @OnError
    public void onError(Session session, Throwable error){
        System.out.println("发生错误");
        error.printStackTrace();
    }
    public static synchronized int getOnlineCount() {
        return onlineCount;
    }
    public static synchronized void addOnlineCount() {
        WebsocketTest.onlineCount++;
    }
    public static synchronized void subOnlineCount() {
        WebsocketTest.onlineCount--;
    }
}