@Configuration
public class WebSocketConfig {
    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }
}

@Component
@ServerEndpoint("/server/{uid}")
@Slf4j
public class WebSocketServer {

    /**
     * 記錄當前在線連接數(shù)
     */
    private static int onlineCount = 0;

    /**
     * 使用線程安全的ConcurrentHashMap來存放每個客戶端對應(yīng)的WebSocket對象
     */
    private static ConcurrentHashMap<String, WebSocketServer> webSocketMap = new ConcurrentHashMap<>();

    /**
     * 與某個客戶端的連接會話，需要通過它來給客戶端發(fā)送數(shù)據(jù)
     */
    private Session session;

    /**
     * 接收客戶端消息的uid
     */
    private String uid = "";

    /**
     * 連接建立成功調(diào)用的方法
     * @param session
     * @param uid
     */
    @OnOpen
    public void onOpen(Session session, @PathParam("uid") String uid) {
        this.session = session;
        this.uid = uid;
        if (webSocketMap.containsKey(uid)) {
            webSocketMap.remove(uid);
            //加入到set中
            webSocketMap.put(uid, this);
        } else {
            //加入set中
            webSocketMap.put(uid, this);
            //在線數(shù)加1
            addOnlineCount();
        }

        log.info("用戶【" + uid + "】連接成功，當前在線人數(shù)為:" + getOnlineCount());
        try {
            sendMsg("連接成功");
        } catch (IOException e) {
            log.error("用戶【" + uid + "】網(wǎng)絡(luò)異常!", e);
        }
    }

    /**
     * 連接關(guān)閉調(diào)用的方法
     */
    @OnClose
    public void onClose() {
        if (webSocketMap.containsKey(uid)) {
            webSocketMap.remove(uid);
            //從set中刪除
            subOnlineCount();
        }
        log.info("用戶【" + uid + "】退出，當前在線人數(shù)為:" + getOnlineCount());
    }

    /**
     * 收到客戶端消息后調(diào)用的方法
     * @param message 客戶端發(fā)送過來的消息
     * @param session 會話
     */
    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("用戶【" + uid + "】發(fā)送報文:" + message);
        //群發(fā)消息
        //消息保存到數(shù)據(jù)庫或者redis
        if (StringUtils.isNotBlank(message)) {
            try {
                //解析發(fā)送的報文
                ObjectMapper objectMapper = new ObjectMapper();
                Map<String, String> map = objectMapper.readValue(message, new TypeReference<Map<String, String>>(){});
                //追加發(fā)送人(防止串改)
                map.put("fromUID", this.uid);
                String toUID = map.get("toUID");
                //傳送給對應(yīng)的toUserId用戶的WebSocket
                if (StringUtils.isNotBlank(toUID) && webSocketMap.containsKey(toUID)) {
                    webSocketMap.get(toUID).sendMsg(objectMapper.writeValueAsString(map));
                } else {
                    //若果不在這個服務(wù)器上，可以考慮發(fā)送到mysql或者redis
                    log.error("請求目標用戶【" + toUID + "】不在該服務(wù)器上");
                }
            } catch (Exception e) {
                log.error("用戶【" + uid + "】發(fā)送消息異常！", e);
            }
        }
    }

    /**
     * 處理錯誤
     * @param session
     * @param error
     */
    @OnError
    public void onError(Session session, Throwable error) {
        log.error("用戶【" + this.uid + "】處理消息錯誤，原因:" + error.getMessage());
        error.printStackTrace();
    }

    /**
     * 實現(xiàn)服務(wù)器主動推送
     * @param msg
     * @throws IOException
     */
    private void sendMsg(String msg) throws IOException {
        this.session.getBasicRemote().sendText(msg);
    }

    /**
     * 發(fā)送自定義消息
     * @param message
     * @param uid
     * @throws IOException
     */
    public static void sendInfo(String message, @PathParam("uid") String uid) throws IOException {
        log.info("發(fā)送消息到用戶【" + uid + "】發(fā)送的報文:" + message);
        if (!StringUtils.isEmpty(uid) && webSocketMap.containsKey(uid)) {
            webSocketMap.get(uid).sendMsg(message);
        } else {
            log.error("用戶【" + uid + "】不在線！");
        }
    }

    private static synchronized int getOnlineCount() {
        return onlineCount;
    }

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

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

}

@RestController
public class WebSocketController {

    @GetMapping("/page")
    public ModelAndView page() {
        return new ModelAndView("webSocket");
    }

    @RequestMapping("/push/{toUID}")
    public ResponseEntity<String> pushToClient(String message, @PathVariable String toUID) throws Exception {
        WebSocketServer.sendInfo(message, toUID);
        return ResponseEntity.ok("Send Success!");
    }
}

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>WebSocket消息通知</title>
</head>
<script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.js"></script>
<script>
    var socket;

    //打開WebSocket
    function openSocket() {
        if (typeof (WebSocket) === "undefined") {
            console.log("您的瀏覽器不支持WebSocket");
        } else {
            console.log("您的瀏覽器支持WebSocket");
            //實現(xiàn)化WebSocket對象，指定要連接的服務(wù)器地址與端口,建立連接.
            var socketUrl = "http://localhost:8080/socket/server/" + $("#uid").val();
            //將https與http協(xié)議替換為ws協(xié)議
            socketUrl = socketUrl.replace("https", "ws").replace("http", "ws");
            console.log(socketUrl);
            if (socket != null) {
                socket.close();
                socket = null;
            }
            socket = new WebSocket(socketUrl);
            //打開事件
            socket.onopen = function () {
                console.log("WebSocket已打開");
                //socket.send("這是來自客戶端的消息" + location.href + new Date());
            };
            //獲得消息事件
            socket.onmessage = function (msg) {
                console.log(msg.data);
                //發(fā)現(xiàn)消息進入,開始處理前端觸發(fā)邏輯
            };
            //關(guān)閉事件
            socket.onclose = function () {
                console.log("WebSocket已關(guān)閉");
            };
            //發(fā)生了錯誤事件
            socket.onerror = function () {
                console.log("WebSocket發(fā)生了錯誤");
            }
        }
    }

    //發(fā)送消息
    function sendMessage() {
        if (typeof (WebSocket) === "undefined") {
            console.log("您的瀏覽器不支持WebSocket");
        } else {
            console.log("您的瀏覽器支持WebSocket");
            console.log('{"toUID":"' + $("#toUID").val() + '","Msg":"' + $("#msg").val() + '"}');
            socket.send('{"toUID":"' + $("#toUID").val() + '","Msg":"' + $("#msg").val() + '"}');
        }
    }
</script>
<body>
<p>【uid】：
<div><input id="uid" name="uid" type="text" value="1"></div>
<p>【toUID】：
<div><input id="toUID" name="toUID" type="text" value="2"></div>
<p>【Msg】：
<div><input id="msg" name="msg" type="text" value="hello WebSocket2"></div>
<p>【第一步操作:】：
<div>
    <button onclick="openSocket()">開啟socket</button>
</div>
<p>【第二步操作:】：
<div>
    <button onclick="sendMessage()">發(fā)送消息</button>
</div>
</body>

</html>