Android File Read and Write

Question

I am new to Android programming and so kingly pardon me if this question sounds stupid. I want to read and write from a file in an Android Program. I am aware of how to do that in Java.

Having read the documentation I wrote the following code. However I am unable to locate where this file is. According to the documentation it should be in folder data/data/package_name.

I have Samsung Galaxy S2. I launched the application, then closed it. When I went looking for the file I could not find it. I looked in My Files/data. But there is no data folder inside this data folder. What am I doing wrong?

Thank you for the help.

Sources: 1. http://developer.android.com/training/basics/data-storage/files.html 2. http://www.vogella.com/articles/AndroidFileBasedPersistence/article.html#overview

public class MainActivity extends Activity {

private void writeFileToInternalStorage() {
      String eol = System.getProperty("line.separator");
      BufferedWriter writer = null;
      try {
        writer = new BufferedWriter(new OutputStreamWriter(openFileOutput("myfile.txt", MODE_WORLD_WRITEABLE)));
        writer.write("This is a test1." + eol);
        writer.write("This is a test2." + eol);
      } catch (Exception e) {
          e.printStackTrace();
      } finally {
        if (writer != null) {
        try {
          writer.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
        }
      }
}   
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    writeFileToInternalStorage();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}

}

it doesnt crash. I am unable to locate the file where data is written to. — Manas Paldhe, Dec 16 '12 at 10:37
to access (outside of the app) the data/data/package_name folder your device must be rooted — Kirill Kulakov, Dec 16 '12 at 10:49
@ManasPaldhe : see this post http://stackoverflow.com/questions/5766609/save-internal-file-in-my-own-internal-folder-in-android CommonsWare answer i hope this will solve your issue — ρяσѕρєя K, Dec 16 '12 at 10:58
@ManasPaldhe To Read and write in external memory so that you can view your files. Read this tutorial here. — Ajay S, Dec 16 '12 at 11:08

score 2 · Answer 1 · answered Dec 16 '12 at 10:43

2

You can use getExternalFilesDir to get the directory on the SDCard where you can write your files. Use null as paramater for general files.

Path will be /mnt/sdcard/Android/data/[package]/files

answered Dec 16 '12 at 10:43

alexghr

96
2

score 1 · Accepted Answer · answered Dec 16 '12 at 10:46

1

Unless and until your phone is rooted or you are using an emulator, I don't think you will able to see private files. Anyways, on the emulator you can always do an "adb shell" and do a "cd /data/data/package_name/" to have a look at the files.

One deprecated option is to set the flags as MODE_WORLD_READABLE or MODE_WORLD_WRITEABLE in the mode section of the openFileOutput(String name, int mode) function.

Else if you want to access it through your file manager, you always have the option of storing non-private data on your phone's external storage. Have a look at the Save a File on External Storage section to know how to do that.

answered Dec 16 '12 at 10:46

sultan.of.swing

1,090
1
12
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I have set the MODE_WORLD_WRITABLE – Manas Paldhe Dec 16 '12 at 10:51
Are you doing an "adb shell" and then looking at the package data directory? – sultan.of.swing Dec 16 '12 at 10:52
I have not tried it on emulator. I am trying it on the real device. – Manas Paldhe Dec 16 '12 at 10:54
how do I choose adb shell? – Manas Paldhe Dec 16 '12 at 10:55
just connect your device to your machine and open a terminal on Windows/Mac/Linux and type "path/to/adb shell" – sultan.of.swing Dec 16 '12 at 10:57
I get the error: mpaldhe@mpaldhe-Latitude-E4300:~$ path/to/adb shell bash: path/to/adb: No such file or directory – Manas Paldhe Dec 16 '12 at 10:59
I meant the path to your adb script, it'll be somewhere in "android-sdk/platform-tools/adb" – sultan.of.swing Dec 16 '12 at 11:02
FYI, I ran the code you posted on an emulator and I am able to see the contents of myfile.txt in the /data/data/package_name folder. – sultan.of.swing Dec 16 '12 at 11:13
how do I access that folder? – Manas Paldhe Dec 16 '12 at 11:20
Are you talking about your app folder? Look at your code, the first line will give u ur package name "package ......" e.g. de.vogella.android.socialapp in the example link u posted, do a "cd de.vogella.android.socialapp" and the do a "cd files", you'll see your mytext.txt file there. – sultan.of.swing Dec 16 '12 at 11:29
ok! Now I am able to reach that folder through sdb, but how do I check the contents? gedit or vim doesnt work as it is not installed app in my phone. So what do I use to "see" that file? – Manas Paldhe Dec 16 '12 at 11:38
Do a "cat myfile.txt", u will be able to see its contents. – sultan.of.swing Dec 16 '12 at 11:40
I get error Permission denied. " cat myfile.txt myfile.txt: Permission denied" – Manas Paldhe Dec 16 '12 at 11:44
You'll need root access on your phone to look at the private data of apps. You can try the example on emulator or root the phone. MODE_WORLD_WRITABLE enables an app to read/write data into files of other apps and does not allow you to read/write the files from your terminal until u have root access. – sultan.of.swing Dec 16 '12 at 11:52
it worked on emulator. I dont have root access on phone. So did not work there. Thanks a lot – Manas Paldhe Dec 16 '12 at 11:56

score 0 · Answer 3 · answered Dec 16 '12 at 10:37

0

openFileOutput() func creates private file accesible by your application. Same as SharedPreferences file (private files). I means like the preference files are hidden but accessible by application in the same way your file is hidden and stored in private memory.. you can access from your code but not with file viewer..

answered Dec 16 '12 at 10:37

kadhirvel

470
1
4
17

so if I want to see the file, how to I change the preferences? – Manas Paldhe Dec 16 '12 at 10:38
in only rooted phones these files can be reterieved from outside your app. – kadhirvel Dec 16 '12 at 10:41
so where do I store the files so that the user can see in non-rooted phones? – Manas Paldhe Dec 16 '12 at 10:42

Ajay S · Answer 4 · 2012-12-16T10:59:01.400

0

You can Read/ Write your File in data/data/package_name/files Folder by,

To Write

BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(new 
                        File(getFilesDir()+File.separator+"MyFile.txt")));
bufferedWriter.write("lalit poptani");
bufferedWriter.close();

To Read

BufferedReader bufferedReader = new BufferedReader(new FileReader(new 
File(getFilesDir()+File.separator+"MyFile.txt")));
String read;
StringBuilder builder = new StringBuilder("");

while((read = bufferedReader.readLine()) != null){
    builder.append(read);
}
Log.d("Output", builder.toString());
bufferedReader.close();

To Read and write in external memory so that you can view your files visually. Read this tutorial here.

edited Dec 16 '12 at 10:59

answered Dec 16 '12 at 10:52

Ajay S

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how can I see this "MyFile.txt"? I mean I want to visually see this file using text editor or something. – Manas Paldhe Dec 16 '12 at 10:54
1

@Manas Paldhe as i know you can not see internal memory files. If you want to see the files then save the files in sdcard and read from sdcard. – Ajay S Dec 16 '12 at 10:55
@Manas Paldhe Read this tutorial http://www.java-samples.com/showtutorial.php?tutorialid=1523 – Ajay S Dec 16 '12 at 10:58
yeah looking through it. Thanks. – Manas Paldhe Dec 16 '12 at 11:13
@ManasPaldhe use this in AndroidManifest.xml ..its must if you write data in external storage... – Ajay S Dec 16 '12 at 11:16

Android File Read and Write

4 Answers4