How to Build QR Code Login with WebSocket in Spring Boot

1. Database Table

We need a User_Token table to record who scanned the QR code and who logged in. The fields are:

uuid – unique identifier

userId – the logged‑in user

loginTime – time of login

createTime – record creation time (used to check expiration)

state – QR code status (0 = valid, 1 = invalid)

2. Roles

The login process involves three roles:

Android or WeChat web client – scans the QR code

PC client – receives the scan and performs the login

Server – provides APIs and coordinates the flow

3. Required APIs

Two REST endpoints are needed:

Generate QR code – creates a QR image that contains a UUID.

Confirm identity – validates the token, checks expiration, and completes the login.

4. Process Steps

PC calls the generate‑QR API, receives a UUID in the response header, and displays the QR image.

The web client scans the QR, extracts the UUID, and calls the confirm‑identity API.

If validation succeeds, the server pushes a success message to the PC via WebSocket.

The PC receives the message, stores session data, and redirects to the target page.

5. Backend Code – Generate QR

<code>//获取登录二维码、放入Token
@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 {
        // Generate a UUID and store it in the database
        String uuid = userService.createQrImg();
        response.setHeader("uuid", uuid);
        // Use Hutool's QrCodeUtil to generate the image
        QrCodeUtil.generate(uuid, 300, 300, "jpg", response.getOutputStream());
    } catch (Exception e) {
        e.printStackTrace();
    }
}
</code>

6. Frontend Code – Load QR and Open WebSocket

<code>$(document).ready(function(){
    initQrImg();
});

function initQrImg(){
    $("#qrImgDiv").empty();
    var xmlhttp = new XMLHttpRequest();
    xmlhttp.open("GET", getQrPath, true);
    xmlhttp.responseType = "blob";
    xmlhttp.onload = function(){
        console.log(this);
        uuid = this.getResponseHeader("uuid");
        if(this.status == 200) {
            var blob = this.response;
            var img = document.createElement("img");
            img.className = 'qrCodeBox-img';
            img.onload = function(e) { window.URL.revokeObjectURL(img.src); };
            img.src = window.URL.createObjectURL(blob);
            document.getElementById("qrImgDiv").appendChild(img);
            initWebSocket();
        }
    };
    xmlhttp.send();
}

var path = "://localhost:8085";
var getQrPath = "http" + path + "/user/getLoginQr";
var wsPath = "ws" + path + "/websocket/";

function initWebSocket(){
    if(typeof(WebSocket) == "undefined") {
        console.log("Your browser does not support WebSocket");
    } else {
        console.log("Your browser supports WebSocket");
        var wsPathStr = wsPath + uuid;
        socket = new WebSocket(wsPathStr);
        socket.onopen = function() { console.log("Socket opened"); };
        socket.onmessage = function(msg) {
            console.log(msg.data);
            var data = JSON.parse(msg.data);
            if(data.code == 200){
                alert("Login successful!");
                window.sessionStorage.uuid = uuid;
                window.sessionStorage.userId = data.userId;
                window.sessionStorage.projId = data.projId;
                window.location.href = "pages/upload.html";
            } else {
                socket.close();
                initQrImg();
            }
        };
        socket.onclose = function() { console.log("Socket closed"); };
        socket.onerror = function() { alert("Socket error"); };
    }
}
</code>

7. Spring Boot WebSocket Configuration

<code>&lt;dependency&gt;
    &lt;groupId&gt;org.springframework.boot&lt;/groupId&gt;
    &lt;artifactId&gt;spring-boot-starter-websocket&lt;/artifactId&gt;
&lt;/dependency&gt;
</code>

<code>@Bean
public ServerEndpointExporter serverEndpointExporter() {
    return new ServerEndpointExporter();
}
</code>

<code>@ServerEndpoint("/websocket/{sid}")
@Component
public class WebSocketServer {
    private static Log log = LogFactory.get(WebSocketServer.class);
    private static int onlineCount = 0;
    private static CopyOnWriteArraySet&lt;WebSocketServer&gt; webSocketSet = new CopyOnWriteArraySet&lt;&gt;();
    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("Received from " + sid + ": " + message);
        for (WebSocketServer item : webSocketSet) {
            try { item.sendMessage(message); } catch (IOException e) { e.printStackTrace(); }
        }
    }

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

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

    public static void sendInfo(String message, @PathParam("sid") String sid) throws IOException {
        for (WebSocketServer item : webSocketSet) {
            if (sid == null || item.sid.equals(sid)) {
                try { item.sendMessage(message); } catch (IOException e) { continue; }
            }
        }
    }

    public static synchronized int getOnlineCount() { return onlineCount; }
    public static synchronized void addOnlineCount() { onlineCount++; }
    public static synchronized void subOnlineCount() { onlineCount--; }
}
</code>

8. Confirm‑Identity API

<code>@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());
    }
}
</code>

<code>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 i = 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 (i > 0) { return null; } else { throw new Exception("Server error!"); }
}
</code>

The overall logic is: the PC obtains a UUID via the QR‑generation API, the mobile/web client scans the QR and calls the confirm‑identity API with the UUID and user ID, the server validates the token and expiration, updates the database, and pushes a success message to the PC through WebSocket, completing the login flow.