Implementing QR Code Login with WebSocket in Spring Boot

In a new Java project the author demonstrates a QR‑code login flow that replaces traditional Ajax polling with a WebSocket‑based solution.

A User_Token table is defined to store uuid , userId , loginTime , createTime , and state (0 = valid, 1 = invalid).

The system involves three roles: the Android/WeChat web client that scans the QR code, the PC client that receives the login request, and the backend server that orchestrates the process.

Two REST APIs are required: one to generate the QR code (embedding a UUID) and another to confirm the identity and check expiration.

The implementation steps are:

PC client calls the QR‑generation API and opens a WebSocket connection using the returned UUID.

The mobile/web client scans the QR code, extracts the UUID, and displays a confirmation page.

After user confirmation, the mobile/web client calls the identity‑confirmation API.

The server validates the token, updates the database, and pushes a success message to the PC client via WebSocket, then closes the connection.

Below are the essential code snippets.

// QR code generation endpoint (Spring MVC)
@RequestMapping(value = "/getLoginQr", method = RequestMethod.GET)
public void createCodeImg(HttpServletRequest request, HttpServletResponse response) {
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);
    response.setContentType("image/jpeg");
    try {
        String uuid = userService.createQrImg();
        response.setHeader("uuid", uuid);
        // Using Hutool's QrCodeUtil to generate the image
        QrCodeUtil.generate(uuid, 300, 300, "jpg", response.getOutputStream());
    } catch (Exception e) {
        e.printStackTrace();
    }
}

// Front‑end JavaScript to fetch QR image and open WebSocket
$(document).ready(function(){ initQrImg(); });
function initQrImg(){
    $("#qrImgDiv").empty();
    var xmlhttp = new XMLHttpRequest();
    xmlhttp.open("GET", getQrPath, true);
    xmlhttp.responseType = "blob";
    xmlhttp.onload = function(){
        var uuid = this.getResponseHeader("uuid");
        if (this.status == 200) {
            var blob = this.response;
            var img = document.createElement("img");
            img.className = 'qrCodeBox-img';
            img.onload = function(){ window.URL.revokeObjectURL(img.src); };
            img.src = window.URL.createObjectURL(blob);
            document.getElementById("qrImgDiv").appendChild(img);
            initWebSocket(uuid);
        }
    };
    xmlhttp.send();
}
function initWebSocket(uuid){
    if (typeof(WebSocket) == "undefined") { console.log("Browser does not support WebSocket"); return; }
    var ws = new WebSocket("ws://localhost:8085/websocket/" + uuid);
    ws.onopen = function(){ console.log("Socket opened"); };
    ws.onmessage = function(msg){
        var data = JSON.parse(msg.data);
        if (data.code == 200){
            alert("Login successful!");
            sessionStorage.uuid = uuid;
            sessionStorage.userId = data.userId;
            sessionStorage.projId = data.projId;
            location.href = "pages/upload.html";
        } else {
            ws.close();
            initQrImg();
        }
    };
    ws.onclose = function(){ console.log("Socket closed"); };
    ws.onerror = function(){ alert("Socket error"); };
}

// WebSocket server implementation (Spring Boot)
@ServerEndpoint("/websocket/{sid}")
@Component
public class WebSocketServer {
    private static Log log = LogFactory.get(WebSocketServer.class);
    private static int onlineCount = 0;
    private static CopyOnWriteArraySet
webSocketSet = new CopyOnWriteArraySet<>();
    private Session session;
    private String sid = "";

    @OnOpen
    public void onOpen(Session session, @PathParam("sid") String sid) {
        this.session = session;
        webSocketSet.add(this);
        addOnlineCount();
        log.info("New connection: " + sid + ", online: " + getOnlineCount());
        this.sid = sid;
    }

    @OnClose
    public void onClose() {
        webSocketSet.remove(this);
        subOnlineCount();
        log.info("Connection closed, online: " + getOnlineCount());
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("Message from " + sid + ": " + message);
        for (WebSocketServer client : webSocketSet) {
            try { client.sendMessage(message); } catch (IOException e) { e.printStackTrace(); }
        }
    }

    @OnError
    public void onError(Session session, Throwable error) {
        log.error("Error: ");
        error.printStackTrace();
    }

    public void sendMessage(String message) throws IOException {
        this.session.getBasicRemote().sendText(message);
    }

    public static void sendInfo(String message, String sid) throws IOException {
        for (WebSocketServer client : webSocketSet) {
            if (sid == null || client.sid.equals(sid)) {
                client.sendMessage(message);
            }
        }
    }

    // Synchronized counters
    public static synchronized int getOnlineCount() { return onlineCount; }
    public static synchronized void addOnlineCount() { onlineCount++; }
    public static synchronized void subOnlineCount() { onlineCount--; }
}

// Controller for confirming identity
@RequestMapping(value = "/bindUserIdAndToken", method = RequestMethod.GET)
@ResponseBody
public Object bindUserIdAndToken(@RequestParam("token") String token,
                                 @RequestParam("userId") Integer userId,
                                 @RequestParam(required = false, value = "projId") Integer projId) {
    try {
        return new SuccessTip(userService.bindUserIdAndToken(userId, token, projId));
    } catch (Exception e) {
        e.printStackTrace();
        return new ErrorTip(500, e.getMessage());
    }
}

// Service method handling token validation and login
@Override
public String bindUserIdAndToken(Integer userId, String token, Integer projId) throws Exception {
    QrLoginToken qrLoginToken = new QrLoginToken();
    qrLoginToken.setToken(token);
    qrLoginToken = qrLoginTokenMapper.selectOne(qrLoginToken);
    if (qrLoginToken == null) {
        throw new Exception("Invalid request!");
    }
    Date expireTime = new Date(qrLoginToken.getCreateTime().getTime() + 1000 * 60 * Constant.LOGIN_VALIDATION_TIME);
    if (new Date().after(expireTime)) {
        JSONObject json = new JSONObject();
        json.put("code", 500);
        json.put("msg", "QR code expired!");
        WebSocketServer.sendInfo(json.toJSONString(), token);
        throw new Exception("QR code expired!");
    }
    qrLoginToken.setLoginTime(new Date());
    qrLoginToken.setUserId(userId);
    int updated = qrLoginTokenMapper.updateById(qrLoginToken);
    JSONObject json = new JSONObject();
    json.put("code", 200);
    json.put("msg", "ok");
    json.put("userId", userId);
    if (ToolUtil.isNotEmpty(projId)) { json.put("projId", projId); }
    WebSocketServer.sendInfo(json.toJSONString(), token);
    if (updated > 0) return null;
    else throw new Exception("Server error!");
}

The overall flow validates the token, checks expiration, updates the login record, and pushes a success message to the PC client via WebSocket, after which the front‑end proceeds with its business logic.