<WebView
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:id="@+id/webView"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"
    android:layout_alignParentBottom="true"
    android:layout_alignParentRight="true"
    android:layout_alignParentEnd="true"
    tools:ignore="MissingConstraints" />

import android.os.Bundle;
import android.webkit.WebView;
import android.webkit.WebViewClient;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    String websiteURL = "https://www.jcserver.in/"; // sets web url
    private WebView webview;

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

        //Webview stuff
        webview = findViewById(R.id.webView);
        webview.getSettings().setJavaScriptEnabled(true);
        webview.getSettings().setDomStorageEnabled(true);
        webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
        webview.loadUrl(websiteURL);
        webview.setWebViewClient(new WebViewClientDemo());

    }

    private class WebViewClientDemo extends WebViewClient {
        @Override
        //Keep webview in app when clicking links
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }
    }

}

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

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

import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.util.Log;
import android.webkit.WebView;
import android.webkit.WebViewClient;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    String websiteURL = "https://www.jcserver.in/"; // sets web url
    private WebView webview;

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

        if( ! CheckNetwork.isInternetAvailable(this)) //returns true if internet available
        {
            //if there is no internet do this
            setContentView(R.layout.activity_main);
            //Toast.makeText(this,"No Internet Connection, Chris",Toast.LENGTH_LONG).show();

            new AlertDialog.Builder(this) //alert the person knowing they are about to close
                    .setTitle("No internet connection available")
                    .setMessage("Please Check you're Mobile data or Wifi network.")
                    .setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                        @Override
                        public void onClick(DialogInterface dialog, int which) {
                            finish();
                        }
                    })
                    //.setNegativeButton("No", null)
                    .show();

        }
        else
        {
            //Webview stuff
            webview = findViewById(R.id.webView);
            webview.getSettings().setJavaScriptEnabled(true);
            webview.getSettings().setDomStorageEnabled(true);
            webview.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
            webview.loadUrl(websiteURL);
            webview.setWebViewClient(new WebViewClientDemo());

        }
    }

    private class WebViewClientDemo extends WebViewClient {
        @Override
        //Keep webview in app when clicking links
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }
    }

}

class CheckNetwork {

    private static final String TAG = CheckNetwork.class.getSimpleName();

    public static boolean isInternetAvailable(Context context)
    {
        NetworkInfo info = (NetworkInfo) ((ConnectivityManager)
                context.getSystemService(Context.CONNECTIVITY_SERVICE)).getActiveNetworkInfo();

        if (info == null)
        {
            Log.d(TAG,"no internet connection");
            return false;
        }
        else
        {
            if(info.isConnected())
            {
                Log.d(TAG," internet connection available...");
                return true;
            }
            else
            {
                Log.d(TAG," internet connection");
                return true;
            }

        }
    }
}

//set back button functionality
@Override
public void onBackPressed() { //if user presses the back button do this
    if (webview.isFocused() && webview.canGoBack()) { //check if in webview and the user can go back
        webview.goBack(); //go back in webview
    } else { //do this if the webview cannot go back any further

        new AlertDialog.Builder(this) //alert the person knowing they are about to close
                .setTitle("EXIT")
                .setMessage("Are you sure. You want to close this app?")
                .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        finish();
                    }
                })
                .setNegativeButton("No", null)
                .show();
    }
}

<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
    android:id="@+id/swipeContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <WebView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:id="@+id/webView"
        android:layout_alignParentTop="true"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_alignParentEnd="true"
        tools:ignore="MissingConstraints" />

</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>

SwipeRefreshLayout mySwipeRefreshLayout;

//Swipe to refresh functionality
mySwipeRefreshLayout = (SwipeRefreshLayout)this.findViewById(R.id.swipeContainer);

mySwipeRefreshLayout.setOnRefreshListener(
        new SwipeRefreshLayout.OnRefreshListener() {
            @Override
            public void onRefresh() {
                webview.reload();
            }
        }
);

private class WebViewClientDemo extends WebViewClient {
    @Override
    //Keep webview in app when clicking links
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
    @Override
    public void onPageFinished(WebView view, String url) {
        super.onPageFinished(view, url);
        mySwipeRefreshLayout.setRefreshing(false);
    }
}

android:screenOrientation="portrait">

import androidx.appcompat.app.AppCompatActivity;

    import android.content.Intent;

    import android.os.Bundle;

    import android.view.Window;

    import android.view.WindowManager;

    public class SplashActivity extends AppCompatActivity {

        @Override

        protected void onCreate(Bundle savedInstanceState) {

            super.onCreate(savedInstanceState);

            Window window = getWindow() ;

            window.addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);

            setContentView(R.layout.activity_splash);

            Thread splashTread = new Thread(){

                @Override

                public void run() {

                    try {

                        sleep(3000);

                        startActivity(new Intent(getApplicationContext(),MainActivity.class));

                        finish();

                    } catch (InterruptedException e) {

                        e.printStackTrace();

                    }

                    super.run();

                }

            };

            splashTread.start();

        }

    }

<?xml version="1.0" encoding="utf-8"?>

    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

        xmlns:app="http://schemas.android.com/apk/res-auto"

        xmlns:tools="http://schemas.android.com/tools"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:orientation="vertical"

        tools:context=".SplashActivity">

        <ImageView

            android:layout_width="match_parent"

            android:layout_height="300dp"

            android:src="@drawable/logo"

            android:scaleType="centerCrop"

            android:padding="50dp"

            android:layout_marginTop="220dp"/>

        <ProgressBar

            android:layout_width="220dp"

            android:layout_height="10dp"

            android:layout_gravity="center_horizontal"

            style="?android:attr/progressBarStyleHorizontal"

            android:max="100"

            android:indeterminate="true"

            android:progress="0"

            android:layout_marginTop="100dp"

            />

    </LinearLayout>

<activity
            android:name=".MainActivity"
            android:exported="false" />
        <activity
            android:name=".SplashActivity"
            android:exported="true"
            android:screenOrientation="portrait">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

if(Build.VERSION.SDK_INT>= Build.VERSION_CODES.M){
            if(checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_DENIED){

                Log.d("permission","permission denied to WRITE_EXTERNAL_STORAGE - requesting it");
                String[] permissions = {Manifest.permission.WRITE_EXTERNAL_STORAGE};
                requestPermissions(permissions,1);
            }

        }

//handle downloading

webview.setDownloadListener(new DownloadListener() {
            @Override
            public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimeType, long contentLength) {

                DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
                request.setMimeType(mimeType);
                String cookies = CookieManager.getInstance().getCookie(url);
                request.addRequestHeader("cookie",cookies);
                request.addRequestHeader("User-Agent",userAgent);
                request.setDescription("Downloading file....");
                request.setTitle(URLUtil.guessFileName(url,contentDisposition,mimeType));
                request.allowScanningByMediaScanner();
                request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
                request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS,URLUtil.guessFileName(url, contentDisposition, mimeType));
                DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
                dm.enqueue(request);
                Toast.makeText(getApplicationContext(),"Downloading File",Toast.LENGTH_SHORT).show();

            }
        });

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