How can i make the first screen of my flutter show up before executing native based java code that will fetch data using a java library

i was working on some project with flutter that has to fetch data from the internet i tried to get it done using dart but it was not possible so i decided to do it in java and it works the problem the native java code started executing before the loading screen shows up on the screen and it shows some white screen and after that it just goes to the homepage is there anyway that i can make my loading screen appear first and then load the data from the internet as the loading screen is showing while the user waits and push the screen to the home screen after the loading is over.
i have tried putting sleep Duration for one second so that it can render the loading screen first but it didn't work.

Here is my java code

public class MainActivity extends FlutterActivity {
private static final String CHANNEL = "samples.flutter.dev/battery";
@Override
public  void configureFlutterEngine( FlutterEngine flutterEngine) {
super.configureFlutterEngine(flutterEngine);
new MethodChannel(flutterEngine.getDartExecutor().getBinaryMessenger(), CHANNEL)
.setMethodCallHandler(
(call, result) -> {
if (call.method.equals("getDate")) {
try {
result.success(getReal2());
} catch (InterruptedException e) {
e.printStackTrace();
} catch (ExecutionException e) {
e.printStackTrace();
}
}
else {
result.notImplemented();
}
}
);
}
public static List getCoffee() throws IOException {
ArrayList coffee = new ArrayList();
Document doc;
doc= Jsoup.connect("https://www.bankofabyssinia.com").timeout(6000).get();
for(int i=0;i<=8;i++) {
for (int j=2;j<=3;j++){
coffee.add(doc.select(" #myTable > tbody > tr:nth-child("+i+") > td:nth-child("+j+")").text());
}
}
return coffee;
}
@TargetApi(Build.VERSION_CODES.N)
public List getReal2() throws ExecutionException, InterruptedException {
CompletableFuture<List > completableFuture = CompletableFuture.supplyAsync(() -> {
try {
return getCoffee();
} catch (IOException e) {
e.printStackTrace();
}
return null;
});
while (!completableFuture.isDone()) {
}
List result = completableFuture.get();
return  result;
}
}

and here is my flutter code

import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'Home.dart';
class Load extends StatefulWidget {
@override
_LoadState createState() => _LoadState();
}
class _LoadState extends State<Load> {
static const platform = const MethodChannel('samples.flutter.dev/battery');
void getWholeJava() async {
try {
final List result = await platform.invokeMethod('getDate');
Navigator.of(context).pushReplacement(MaterialPageRoute(
builder: (BuildContext context) => Home(
whole: result,
)));
} on PlatformException catch (e) {
print(e);
}
}
@override
void initState() {
// TODO: implement initState
super.initState();
getWholeJava();
}
@override
Widget build(BuildContext context) {
return Scaffold(body: Builder(builder: (BuildContext context) {
return Container(
child: Center(
child: Column(
children: <Widget>[
Text(
'The app is loading',
style: TextStyle(
fontSize: 40.0,
fontWeight: FontWeight.w900,
color: Colors.green[900]),
),
],
)),
);
}));
}
}

First, android will default to its launch screen, which is managed by launch_background.xml inside the template flutter android project. This means that you will need to use a background color for the splash screen, that will work with the android native launch screen drawable.

Next, to implement a splash screen, that will then navigate to a page, where you can run and load your data, you can look at this:

import 'package:async/async.dart';
class SampleSplashScreenPage extends StatefulWidget {
@override
_SampleSplashScreenPageState createState() => new _SampleSplashScreenPageState();
}
class _SampleSplashScreenPageState extends State<SampleSplashScreenPage> {
@override
void initState() {
super.initState();
new RestartableTimer(new Duration(seconds: 3), () async {
await Navigator.push(context, MaterialPageRoute(builder: (_) {
return FlutterDataLoadingPage();
}));
});
}
@override
Widget build(BuildContext context) {
return new Text("Your splash screen");
}

RestartableTimer is a class that will begin a stopwatch, and will count up to the designated duration. Once this duration is reached, it will then invoke the handler you pass to it, which in this case is the navigation logic to the page responsible for reading the remote data. This counter by the way does not restart, and will automatically be disposed by the garbage collector.

Take a look at the documentation to learn more:
https://api.flutter.dev/flutter/package-async_async/RestartableTimer-class.html