Android : How to add spinner loader (NOT PROGRESS BAR) before webview loads a webpage in Android?

I have a webview inside Alert Dialog. How can i show loader spinner (NOT PROGRESS BAR) before webview loads and then hide once webpage is loaded ? Below is my code. Here i am not using any xml for webview, its dynamically generated simple webview :

WebView wv = new WebView(activity);
            wv.loadUrl("https://www.yahoo.com");
            wv.getSettings().setJavaScriptEnabled(true);
            wv.getSettings().setBuiltInZoomControls(true);
            wv.getSettings().setSupportZoom(true);
            wv.getSettings().setUseWideViewPort(true);
            wv.setClickable(true);
            wv.setInitialScale(1);
            wv.setWebViewClient(new WebViewClient() {

                @Override
                public boolean shouldOverrideUrlLoading(WebView view, String url) {
                    //view.loadUrl(url);
                    //return true;
                    String cleanUrl = url;
                    if (url.contains("?")) {
                        // remove the query string
                        cleanUrl = url.substring(0,url.indexOf("?"));
                    }

                    if (cleanUrl.endsWith("pdf")) {
                        Intent intent = new Intent(Intent.ACTION_VIEW);
                        intent.setDataAndType(Uri.parse(url), "application/pdf");
                        try {
                            Uri uriUrl = Uri.parse(cleanUrl);
                            Intent intentUrl = new Intent(Intent.ACTION_VIEW, uriUrl);
                            view.getContext().startActivity(intentUrl);
                            return true;

                        } catch (Exception e) {
                            System.out.println(e);
                            Toast.makeText(context,"No PDF Viewer Installed", Toast.LENGTH_LONG).show();
                        }
                    } else {
                        view.loadUrl(url);
                    }
                    return true;
                }

            });

            builder.setView(wv);
            builder.show();