How do you write to a folder on an SD card in Android?

I am using the following code to download a file from my server then write it to the root directory of the SD card, it all works fine:

package com.downloader;

import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.os.Environment;
import android.util.Log;

public class Downloader {

    public void DownloadFile(String fileURL, String fileName) {
        try {
            File root = Environment.getExternalStorageDirectory();
            URL u = new URL(fileURL);
            HttpURLConnection c = (HttpURLConnection) u.openConnection();
            c.setRequestMethod("GET");
            c.setDoOutput(true);
            c.connect();
            FileOutputStream f = new FileOutputStream(new File(root, fileName));

            InputStream in = c.getInputStream();

            byte[] buffer = new byte[1024];
            int len1 = 0;
            while ((len1 = in.read(buffer)) > 0) {
                f.write(buffer, 0, len1);
            }
            f.close();
        } catch (Exception e) {
            Log.d("Downloader", e.getMessage());
        }

    }
}

However, using Environment.getExternalStorageDirectory(); means that the file will always write to the root /mnt/sdcard. Is it possible to specify a certain folder to write the file to?

For example: /mnt/sdcard/myapp/downloads

Solution 1:

File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdCard.getAbsolutePath() + "/dir1/dir2");
dir.mkdirs();
File file = new File(dir, "filename");

FileOutputStream f = new FileOutputStream(file);
...

Solution 2:

Add Permission to Android Manifest

Add this WRITE_EXTERNAL_STORAGE permission to your applications manifest.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="your.company.package"
    android:versionCode="1"
    android:versionName="0.1">
    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <!-- ... -->
    </application>
    <uses-sdk android:minSdkVersion="7" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
</manifest> 

Check availability of external storage

You should always check for availability first. A snippet from the official android documentation on external storage.

boolean mExternalStorageAvailable = false;
boolean mExternalStorageWriteable = false;
String state = Environment.getExternalStorageState();

if (Environment.MEDIA_MOUNTED.equals(state)) {
    // We can read and write the media
    mExternalStorageAvailable = mExternalStorageWriteable = true;
} else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
    // We can only read the media
    mExternalStorageAvailable = true;
    mExternalStorageWriteable = false;
} else {
    // Something else is wrong. It may be one of many other states, but all we need
    //  to know is we can neither read nor write
    mExternalStorageAvailable = mExternalStorageWriteable = false;
}

Use a Filewriter

At last but not least forget about the FileOutputStream and use a FileWriter instead. More information on that class form the FileWriter javadoc. You'll might want to add some more error handling here to inform the user.

// get external storage file reference
FileWriter writer = new FileWriter(getExternalStorageDirectory()); 
// Writes the content to the file
writer.write("This\n is\n an\n example\n"); 
writer.flush();
writer.close();