[网络协议]springboot整合WebSocket：后台服务主动发送信息给前端客户端

1.前端websocket开启方法

    // WebSocket接收消息推送
    openSocket() {
      if (typeof WebSocket == "undefined") {
        console.log("您的浏览器不支持WebSocket");
      } else {
        var socketUrl = `http://localhost:8080/ws/` + this.user.id;
        socketUrl = socketUrl.replace("https","wss")
            .replace("http","ws");
        if (this.socket != null) {
          this.socket.close();
          this.socket = null;
        }
        this.socket = new WebSocket(socketUrl);
        // 打开事件
        this.socket.onopen = function () {
          // console.log("websocket已打开");
        };
        // 获得消息事件
        const _this = this
        this.socket.onmessage = function (msg) {
          console.log(msg.data);//输出从后台接收的信息：“发送测试信息”
          _this.todoSomeThing(_this.user.id)//接收后台发送的请求，主动调用相应的业务接口
        };
        // 关闭事件
        this.socket.onclose = function (e) {
          // console.log("websocket已关闭");
        };
        // 发生了错误事件
        this.socket.onerror = function (e) {
          console.log('websocket发生了错误，错误: ')
          console.log(e)
        };
      }
    }

2.后台()

pom.xml

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

配置类WebSocketConfig.java

package com.test.websocket.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;

/**
 * @Description 启用WebSocket配置类
 */
@Configuration
public class WebSocketConfig {
    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}

服务类WebSocketServer.java

package com.test.websocket.service;

import com.test.common.copycat.utils.StringUtils;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;

import javax.websocket.OnClose;
import javax.websocket.OnError;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;

/**
 * @Description WebSocketServer服务类
 */
@ServerEndpoint("/ws/{userId}")
@Component
@Slf4j
public class WebSocketServer {

    /**静态变量，用来记录当前在线连接数。应该把它设计成线程安全的。*/
    private static int onlineCount = 0;
    /**concurrent包的线程安全Set，用来存放每个客户端对应的MyWebSocket对象。*/
    private static ConcurrentHashMap<String,WebSocketServer> webSocketMap = new ConcurrentHashMap<>();
    /**与某个客户端的连接会话，需要通过它来给客户端发送数据*/
    private Session session;
    /**接收userId*/
    private String userId="";

    /**
     * 连接建立成功调用的方法
     *
     */
    @OnOpen
    public void onOpen(Session session, @PathParam("userId") String userId) {
        this.session = session;
        this.userId = userId;
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);
            webSocketMap.put(userId,this);
        }else{
            webSocketMap.put(userId,this);
            addOnlineCount();
        }
        log.info("用户连接:"+userId+",当前在线人数为:" + getOnlineCount());
//        try {
//            sendMessage("连接成功");
//        } catch (IOException e) {
//            log.error("用户:"+userId+",网络异常!");
//        }
    }

    /**
     * 连接关闭调用的方法
     *
     */
    @OnClose
    public void onClose() {
        if(webSocketMap.containsKey(userId)){
            webSocketMap.remove(userId);

            subOnlineCount();
        }
        log.info("用户退出:"+userId+",当前在线人数为:" + getOnlineCount());
    }

    /**
     * 收到客户端消息后调用的方法
     *
     * @param message 客户端发送过来的消息
     */
    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("用户消息:"+userId+",报文:"+message);
        if(StringUtils.isNotBlank(message)){
            try {
                //解析发送的报文
                JSONObject jsonObject = JSON.parseObject(message);
                //追加发送人(防止串改)
                jsonObject.put("fromUserId",this.userId);
                String toUserId=jsonObject.getString("toUserId");
                //传送给对应toUserId用户的websocket
                if(StringUtils.isNotBlank(toUserId) && webSocketMap.containsKey(toUserId)){
                    webSocketMap.get(toUserId).sendMessage(jsonObject.toJSONString());
                }else{
                    log.error("请求的userId:"+toUserId+"不在该服务器上");
                }
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    }

    /**
     * 连接错误调用的方法
     *
     * @param session
     * @param error
     */
    @OnError
    public void onError(Session session, Throwable error) {
        log.error("用户错误:"+this.userId+",原因:"+error.getMessage());
        error.printStackTrace();
    }

    /**
     * 服务器主动推送消息
     *
     */
    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }

    /**
     * 发送自定义消息
     *
     */
    public static void sendInfo(String message, @PathParam("userId") Long userId) throws IOException {
        log.info("发送消息到:"+userId+"，报文:"+message);
        if(userId!= null &&webSocketMap.containsKey(userId+"")){
            webSocketMap.get(userId+"").sendMessage(message);
        }else{
            log.error("用户"+userId+",不在线！");
        }
    }

    /**
     * 获取在线人数
     *
     */
    public static synchronized int getOnlineCount() {
        return onlineCount;
    }

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

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

其他业务类调用：

 try {
     WebSocketServer.sendInfo("发送测试信息", param.getUserId());
 } catch (IOException e) {
     e.printStackTrace();
 }