Unable to Save Download Facebook Image from WebView on Long Press Image

Help me to download facebook image like Post story

how i can download facebook image by press on click on facebook post and story into them.

Advance modern mobile application web browsers can give the facility to its users to Download Image instantly on Image Long Press event in WebView. i sould going to make a android application in android studio to Download-Save image in mobile phone gallery on Image Long Press.

Code for MainActivity.java file.

package com.android_examples.saveimagefromwebview_android_examplescom;
import android.app.DownloadManager;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.ContextMenu;
import android.view.MenuItem;
import android.view.View;
import android.webkit.URLUtil;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    WebView webView;
    String HTTP_URL = "https://m.facebook.com/" ;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        webView = (WebView)findViewById(R.id.WebView1);

        webView.getSettings().setJavaScriptEnabled(true);

        webView.setWebViewClient(new WebViewClient());

        registerForContextMenu(webView);

        webView.loadUrl(HTTP_URL);
    }

    @Override
    public void onCreateContextMenu(ContextMenu contextMenu, View view, ContextMenu.ContextMenuInfo contextMenuInfo){
        super.onCreateContextMenu(contextMenu, view, contextMenuInfo);

        final WebView.HitTestResult webViewHitTestResult = webView.getHitTestResult();

        if (webViewHitTestResult.getType() == WebView.HitTestResult.IMAGE_TYPE ||
                webViewHitTestResult.getType() == WebView.HitTestResult.SRC_IMAGE_ANCHOR_TYPE) {

            contextMenu.setHeaderTitle("Download Image From Below");

            contextMenu.add(0, 1, 0, "Save - Download Image")
                    .setOnMenuItemClickListener(new MenuItem.OnMenuItemClickListener() {
                        @Override
                        public boolean onMenuItemClick(MenuItem menuItem) {

                            String DownloadImageURL = webViewHitTestResult.getExtra();

                            if(URLUtil.isValidUrl(DownloadImageURL)){

                                DownloadManager.Request request = new DownloadManager.Request(Uri.parse(DownloadImageURL));
                                request.allowScanningByMediaScanner();
                                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                                DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                                downloadManager.enqueue(request);

                                Toast.makeText(MainActivity.this,"Image Downloaded Successfully.",Toast.LENGTH_LONG).show();
                            }
                            else {
                                Toast.makeText(MainActivity.this,"Sorry.. Something Went Wrong.",Toast.LENGTH_LONG).show();
                            }
                            return false;
                        }
                    });
        }
    }
}

Code for activity_main.xml layout file.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.android_examples.saveimagefromwebview_android_examplescom.MainActivity">


    <WebView
        android:id="@+id/WebView1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        />

</RelativeLayout>

Code for AndroidManifest.xml file.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.android_examples.saveimagefromwebview_android_examplescom">

    <uses-permission android:name="android.permission.INTERNET"/>

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>