Zack Tutorials

Android 9 (API level 28) introduces great new features and capabilities for users and developers. Some of the changes impacts File Write and Read. The following is a solution to the File Write / Read problem for pdf files

Code Structure

GenericFileProvider.java

package com.zackdawood;

import android.support.v4.content.FileProvider;

public class GenericFileProvider extends FileProvider {
}


FileDownloader.java
package com.zackdawood;

import android.util.Log;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

public class FileDownloader {

    private static final String TAG = "FileDownloader";

    private static final int MEGABYTE = 1024 * 1024;

    public static void downloadFile(String fileUrl, File directory) {
        try {
            Log.v(TAG, "downloadFile() invoked ");
            Log.v(TAG, "downloadFile() fileUrl " + fileUrl);
            Log.v(TAG, "downloadFile() directory " + directory);

            URL url = new URL(fileUrl);
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.connect();

            InputStream inputStream = urlConnection.getInputStream();
            FileOutputStream fileOutputStream = new FileOutputStream(directory);
            int totalSize = urlConnection.getContentLength();

            byte[] buffer = new byte[MEGABYTE];
            int bufferLength = 0;
            while ((bufferLength = inputStream.read(buffer)) > 0) {
                fileOutputStream.write(buffer, 0, bufferLength);
            }
            fileOutputStream.close();
            Log.v(TAG, "downloadFile() completed ");

        } catch (FileNotFoundException e) {
            e.printStackTrace();
            Log.e(TAG, "downloadFile() error" + e.getMessage());
            Log.e(TAG, "downloadFile() error" + e.getStackTrace());
        } catch (MalformedURLException e) {
            e.printStackTrace();
            Log.e(TAG, "downloadFile() error" + e.getMessage());
            Log.e(TAG, "downloadFile() error" + e.getStackTrace());
        } catch (IOException e) {
            e.printStackTrace();
            Log.e(TAG, "downloadFile() error" + e.getMessage());
            Log.e(TAG, "downloadFile() error" + e.getStackTrace());
        }
    }
}

MainActivity.java
package com.zackdawood;

import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Build;
import android.os.Bundle;
import android.os.Environment;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.FileProvider;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Toast;

import java.io.File;
import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    private static final String[] PERMISSIONS = {android.Manifest.permission.READ_EXTERNAL_STORAGE, android.Manifest.permission.WRITE_EXTERNAL_STORAGE};


    private static boolean hasPermissions(Context context, String... permissions) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && context != null && permissions != null) {
            for (String permission : permissions) {
                if (ActivityCompat.checkSelfPermission(context, permission) != PackageManager.PERMISSION_GRANTED) {
                    return false;
                }
            }
        }
        return true;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Log.v(TAG, "onCreate() Method invoked ");

        ActivityCompat.requestPermissions(MainActivity.this, PERMISSIONS, 112);

    }

    public void request(View view) {

        ActivityCompat.requestPermissions(MainActivity.this, PERMISSIONS, 112);

    }

    public void view(View view) {
        Log.v(TAG, "view() Method invoked ");

        if (!hasPermissions(MainActivity.this, PERMISSIONS)) {

            Log.v(TAG, "download() Method DON'T HAVE PERMISSIONS ");

            Toast t = Toast.makeText(getApplicationContext(), "You don't have read access !", Toast.LENGTH_LONG);
            t.show();

        } else {
            File d = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);  // -> filename = maven.pdf
            File pdfFile = new File(d, "maven.pdf");

            Log.v(TAG, "view() Method pdfFile " + pdfFile.getAbsolutePath());

            Uri path = FileProvider.getUriForFile(this, BuildConfig.APPLICATION_ID + ".fileprovider", pdfFile);


            Log.v(TAG, "view() Method path " + path);

            Intent pdfIntent = new Intent(Intent.ACTION_VIEW);
            pdfIntent.setDataAndType(path, "application/pdf");
            pdfIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
            pdfIntent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);

            try {
                startActivity(pdfIntent);
            } catch (ActivityNotFoundException e) {
                Toast.makeText(MainActivity.this, "No Application available to view PDF", Toast.LENGTH_SHORT).show();
            }
        }
        Log.v(TAG, "view() Method completed ");

    }

    public void download(View view) {
        Log.v(TAG, "download() Method invoked ");

        if (!hasPermissions(MainActivity.this, PERMISSIONS)) {

            Log.v(TAG, "download() Method DON'T HAVE PERMISSIONS ");

            Toast t = Toast.makeText(getApplicationContext(), "You don't have write access !", Toast.LENGTH_LONG);
            t.show();

        } else {
            Log.v(TAG, "download() Method HAVE PERMISSIONS ");

            //new DownloadFile().execute("http://maven.apache.org/maven-1.x/maven.pdf", "maven.pdf");
            new DownloadFile().execute("http://www.axmag.com/download/pdfurl-guide.pdf", "maven.pdf");

        }

        Log.v(TAG, "download() Method completed ");

    }

    private class DownloadFile extends AsyncTask<String, Void, Void> {

        @Override
        protected Void doInBackground(String... strings) {
            Log.v(TAG, "doInBackground() Method invoked ");

            String fileUrl = strings[0];   // -> http://maven.apache.org/maven-1.x/maven.pdf
            String fileName = strings[1];  // -> maven.pdf
            String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
            File folder = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);

            File pdfFile = new File(folder, fileName);
            Log.v(TAG, "doInBackground() pdfFile invoked " + pdfFile.getAbsolutePath());
            Log.v(TAG, "doInBackground() pdfFile invoked " + pdfFile.getAbsoluteFile());

            try {
                pdfFile.createNewFile();
                Log.v(TAG, "doInBackground() file created" + pdfFile);

            } catch (IOException e) {
                e.printStackTrace();
                Log.e(TAG, "doInBackground() error" + e.getMessage());
                Log.e(TAG, "doInBackground() error" + e.getStackTrace());


            }
            FileDownloader.downloadFile(fileUrl, pdfFile);
            Log.v(TAG, "doInBackground() file download completed");

            return null;
        }
    }
}

AndroidManifest.xml

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

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


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

    <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"
        android:networkSecurityConfig="@xml/network_security_config">
        <provider
            android:name=".GenericFileProvider"
            android:authorities="${applicationId}.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/external_files"/>
        </provider>
        <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>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <Button
            android:id="@+id/button3"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="200px"
            android:onClick="download"
            android:text="@string/file_download" />


        <Button
            android:id="@+id/button4"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="200px"
            android:onClick="view"
            android:text="@string/file_view" />

        <Button
            android:id="@+id/button5"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="200px"
            android:onClick="request"
            android:text="@string/file_request" />
    </LinearLayout>


</android.support.design.widget.CoordinatorLayout>
strings.xml
<resources>
    <string name="app_name">DemoInternalDownload</string>
    <string name="action_settings">Settings</string>
    <string name="file_view">File View</string>
    <string name="file_download">File Download</string>
    <string name="file_request">Request Access Again</string>

</resources>

external_files.xml
<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="external_files" path="."/>
</paths>

network_security_config.xml
<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <domain-config cleartextTrafficPermitted="true">
        <domain includeSubdomains="true">maven.apache.org</domain>
        <domain includeSubdomains="true">www.axmag.com</domain>
    </domain-config>
</network-security-config>

build.gradle
apply plugin: 'com.android.application'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.zackdawood"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'com.android.support.test:runner:1.0.2'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
}

Prompt Screen


Output Screen