Android File Writing to Internal Storage

 

A special Note about where the file is located and other apps reading your file

Note: Your app's internal storage directory is specified by your app's package name in a special location of the Android file system. Technically, another app can read your internal files if you set the file mode to be readable. However, the other app would also need to know your app package name and file names. Other apps cannot browse your internal directories and do not have read or write access unless you explicitly set the files to be readable or writable. So as long as you use MODE_PRIVATE for your files on the internal storage, they are never accessible to other apps.

REGARDING MODE_WORLD_* = suggestion is to NOT use

int	MODE_PRIVATE	File creation mode: the default mode, where the created file can only be accessed by the calling application (or all applications sharing the same user ID).
int	MODE_WORLD_READABLE	This constant was deprecated in API level 17. Creating world-readable files is very dangerous, and likely to cause security holes in applications. It is strongly discouraged; instead, applications should use more formal mechanism for interactions such asContentProvider, BroadcastReceiver, and Service. There are no guarantees that this access mode will remain on a file, such as when it goes through a backup and restore. File creation mode: allow all other applications to have read access to the created file.
int	MODE_WORLD_WRITEABLE	This constant was deprecated in API level 17. Creating world-writable files is very dangerous, and likely to cause security holes in applications. It is strongly discouraged; instead, applications should use more formal mechanism for interactions such asContentProvider, BroadcastReceiver, and Service. There are no guarantees that this access mode will remain on a file, such as when it goes through a backup and restore. File creation mode: allow all other applications to have write access to the created file.

 

Step 1: Use java.io.FileOutputStream class to open file, use Activities openFileOutput(*,*) method from Activity class

 

//Inside your Activity class

FileOutputStream fOut = openFileOutput("myFile.txt", MODE_WORLD_READABLE);

 

Other Modes:           MODE_APPEND, MODE_WORLD_WRITEABLE

Step 2: OPTIONAL convert your FileOutputStream instance of step 1 to a easier to use java.io class

OutputStreamWriter osw = new OutputSteramWriter (fOut);

 

Step 3: Write , Flush and Close when done

osw.write("string");

osw.flush();

osw.close();

 

 

 

Android File Reading from Internal Storage

Step 1: Use java.io.FileInputStream class to open file using openFileInput(*) method from Activity class

//inside Activity class

FileInputStream fIn = openFileInput("myFile.txt");

 

 

Step 2: OPTIONAL convert your FileOutputStream instance of step 1 to a easier to use java.io class

InputStreamReader isw = new InputStreamReader (fIn);

 

Step 3: Read and Close when done

int charRead = isw.read();

iws.close();

 

 

 

EXAMPLE: writing and reading to file in Internal Storage

main.xml App's Activity layout   

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 android:orientation="vertical" >
  <TextView
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:text="Please enter some text" />
  <EditText
     android:id="@+id/txtText1" 
     android:layout_width="fill_parent"
     android:layout_height="wrap_content" />
  <Button 
     android:id="@+id/btnSave"
     android:text="Save"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:onClick="onClickSave" />
  <Button 
     android:id="@+id/btnLoad"
     android:text="Load"
     android:layout_width="fill_parent"
     android:layout_height="wrap_content" 
     android:onClick="onClickLoad" />
</LinearLayout>

 

App's Activity    

public class FilesActivity extends Activity {
 EditText textBox;
 static final int READ_BLOCK_SIZE = 100;
 /** Called when the activity is first created. */
   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);

      textBox = (EditText) findViewById(R.id.txtText1);
  
   }


 //CALLED when button asking to Save text user types into textBox is hit
  public void onClickSave(View view) {
      String str = textBox.getText().toString();
      try {
         //---SD Card Storage---   STEP 1: Open up OutputStream to File textfile.txt 
            FileOutputStream fOut = openFileOutput("textfile.txt", MODE_WORLD_READABLE);
         
   
          //STEP 2: Create OutputStreamWriter from FileOutputStream
         OutputStreamWriter osw = new OutputStreamWriter(fOut);

          //---write the string to the file---  STEP 3 write, flush, close
         osw.write(str);
         osw.flush(); 
         osw.close();

          //---display file saved message---
         Toast.makeText(getBaseContext(), "File saved successfully!",Toast.LENGTH_SHORT).show();

         //---clears the EditText---
         textBox.setText("");
      }
      catch (IOException ioe)
      {
         ioe.printStackTrace();
      }
   }



 //CALLED when button asking to Load text user types into textBox is hit
 public void onClickLoad(View view) {
   try {
      //---SD Storage---   //STEP 1 Opening to Read from textfile.txt
      
         FileInputStream fIn =  openFileInput("textfile.txt");
         InputStreamReader isr = new 
         InputStreamReader(fIn);
      
   
      char[] inputBuffer = new char[READ_BLOCK_SIZE];
      String s = "";
      int charRead;
      while ((charRead = isr.read(inputBuffer))>0)     //STEP 3: read from file until eof, -1 returned
         {
            //---convert the chars to a String---
            String readString =  String.copyValueOf(inputBuffer, 0,charRead);
            s += readString;
            inputBuffer = new char[READ_BLOCK_SIZE];
         }
   
      //---set the EditText to the text that has been 
      // read---
      textBox.setText(s);
      Toast.makeText(getBaseContext(), "File loaded successfully!", Toast.LENGTH_SHORT).show();
   }
   catch (IOException ioe) {
      ioe.printStackTrace();
   }
 }

}