SetAsWallpaper/app/src/main/java/net/crystalyx/setaswallpaper/SetWallpaperActivity.java

package net.crystalyx.setaswallpaper;

import android.app.Activity;
import android.app.WallpaperManager;
import android.content.Intent;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.net.Uri;
import android.os.Bundle;
import android.widget.Toast;

import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SetWallpaperActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        Intent intent = getIntent();
        String type = intent.getType();

        if (Intent.ACTION_SEND.equals(intent.getAction()) && type != null) {
            if ("text/plain".equals(type)) {
                handleUrl(intent.getStringExtra(Intent.EXTRA_TEXT));
            } else if (type.startsWith("image/")) {
                handleStream(intent.getParcelableExtra(Intent.EXTRA_STREAM));
            }
        }
    }

    private void handleUrl(String textUrl) {
        URL url;

        try {
            url = new URL(textUrl);
        } catch (MalformedURLException e) {
            Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
            return;
        }

        ExecutorService executor = Executors.newSingleThreadExecutor();

        executor.execute(() -> {
            try {
                URLConnection connection = url.openConnection();
                connection.connect();
                InputStream inputStream = connection.getInputStream();
                launchWallpaperActivity(inputStream);
            } catch (IOException e) {
                Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void handleStream(Uri uri) {
        try {
            InputStream inputStream = getContentResolver().openInputStream(uri);
            launchWallpaperActivity(inputStream);
        } catch (IOException e) {
            Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
        }
    }

    private void launchWallpaperActivity(InputStream stream) {
        WallpaperManager manager = WallpaperManager.getInstance(getApplicationContext());
        Bitmap bitmap = BitmapFactory.decodeStream(stream);

        try {
            manager.setBitmap(bitmap);
        } catch (IOException e) {
            Toast.makeText(this, e.getMessage(), Toast.LENGTH_SHORT).show();
        }

        Toast.makeText(this, "Wallpaper set!", Toast.LENGTH_SHORT).show();
    }

}