Access the http response headers in a WebView?

inspired by Cristian answer I needed to intercept AJAX calls webview is doing, where I needed to intercept response headers to get some information (cart item count in e-commerce app), which I needed to leverage in app. As the app is using okhttp I've ended up doing this and it's working:

        @TargetApi(Build.VERSION_CODES.LOLLIPOP)
        @Override
        public WebResourceResponse shouldInterceptRequest(WebView view, WebResourceRequest request) {
            Log.i(TAG,"shouldInterceptRequest path:"+request.getUrl().getPath());
            WebResourceResponse returnResponse = null;
            if (request.getUrl().getPath().startsWith("/cart")) { // only interested in /cart requests
                returnResponse = super.shouldInterceptRequest(view, request);
                Log.i(TAG,"cart AJAX call - doing okRequest");
                Request okRequest = new Request.Builder()
                        .url(request.getUrl().toString())
                        .post(null)
                        .build();
                try {
                    Response okResponse = app.getOkHttpClient().newCall(okRequest).execute();
                    if (okResponse!=null) {
                        int statusCode = okResponse.code();
                        String encoding = "UTF-8";
                        String mimeType = "application/json";
                        String reasonPhrase = "OK";
                        Map<String,String> responseHeaders = new HashMap<String,String>();
                        if (okResponse.headers()!=null) {
                            if (okResponse.headers().size()>0) {
                                for (int i = 0; i < okResponse.headers().size(); i++) {
                                    String key = okResponse.headers().name(i);
                                    String value = okResponse.headers().value(i);
                                    responseHeaders.put(key, value);
                                    if (key.toLowerCase().contains("x-cart-itemcount")) {
                                        Log.i(TAG,"setting cart item count");
                                        app.setCartItemsCount(Integer.parseInt(value));
                                    }
                                }
                            }
                        }
                        InputStream data = new ByteArrayInputStream(okResponse.body().string().getBytes(StandardCharsets.UTF_8));
                        Log.i(TAG, "okResponse code:" + okResponse.code());
                        returnResponse = new WebResourceResponse(mimeType,encoding,statusCode,reasonPhrase,responseHeaders,data);
                    } else {
                        Log.w(TAG,"okResponse fail");
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return returnResponse;
        }

I hope this may be helpful to others and if somebody has a suggestions for improvement I would be grateful. Unfortunately it's compatible only with LOLLIPOP and higher as from this version you can access/return headers using WebResourceRequest, which was needed for my case.

Neither WebView nor WebViewClient provide methods to do that, Though, you can try to implement that manually. You can do something like this:

private WebView webview;
public void onCreate(Bundle icicle){
    // bla bla bla

    // here you initialize your webview
    webview = new WebView(this);
    webview.setWebViewClient(new YourWebClient());
}

// this will be the webclient that will manage the webview
private class YourWebClient extends WebViewClient{

    // you want to catch when an URL is going to be loaded
    public boolean  shouldOverrideUrlLoading  (WebView  view, String  urlConection){
        // here you will use the url to access the headers.
        // in this case, the Content-Length one
        URL url;
        URLConnection conexion;
        try {
            url = new URL(urlConection);
            conexion = url.openConnection();
            conexion.setConnectTimeout(3000);
            conexion.connect();
            // get the size of the file which is in the header of the request
            int size = conexion.getContentLength();
        }


        // and here, if you want, you can load the page normally
        String htmlContent = "";
        HttpGet httpGet = new HttpGet(urlConection);
        // this receives the response
        HttpResponse response;
        try {
            response = httpClient.execute(httpGet);
            if (response.getStatusLine().getStatusCode() == 200) {
                // la conexion fue establecida, obtener el contenido
                HttpEntity entity = response.getEntity();
                if (entity != null) {
                    InputStream inputStream = entity.getContent();
                    htmlContent = convertToString(inputStream);
                }
            }
         } catch (Exception e) {}

         webview.loadData(htmlContent, "text/html", "utf-8");
         return true;
    }

    public String convertToString(InputStream inputStream){
        StringBuffer string = new StringBuffer();
        BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream));
        String line;
        try {
            while ((line = reader.readLine()) != null) {
                string.append(linea + "\n");
            }
        } catch (IOException e) {}
        return string.toString();
    }
}

I can't test it right now, but that's basically what you could do (it's very crazy though :).