Writing and reading from a file in Android.

openFileOutput() is the method defined in ContextWrapper class used for creating a FileOutputStream for writing to a file.
openFileInput() is the method defined in ContextWrapper class used for creating a FileInputStream for readinf reading from a file.
ContextWrapper is the parent class of ContextThemeWrapper which is the parent of the Activity class.

Write to a file.
[code language=”java”]
private void writeFile(String stringToSave) throws IOException {
FileOutputStream outStream = null;
try {
outStream = openFileOutput(fileName, Context.MODE_PRIVATE);
outStream.write(stringToSave.getBytes());
if (fileExists()) {
displayText("File saved.");
} else {
displayText("File not saved.");
}
} catch (Exception e) {
errorNotification(e.getMessage());
} finally {
outStream.close();
}
}
[/code]

Read from a file.
[code language=”java”]
private String readFile() throws IOException {
FileInputStream inStream = null;
InputStreamReader myInputStreamReader = null;
BufferedReader myBufferedReader = null;
String retrievedString = "";
try {
inStream = openFileInput(fileName);
myInputStreamReader = new InputStreamReader(inStream);
myBufferedReader = new BufferedReader(myInputStreamReader);
String readLineString = myBufferedReader.readLine();
while (readLineString != null) {
retrievedString = retrievedString + readLineString;
readLineString = myBufferedReader.readLine();
}
} catch (IOException ioe) {
errorNotification(ioe.getMessage());
} finally {
myBufferedReader.close();
myInputStreamReader.close();
inStream.close();
}
return retrievedString;
}
[/code]

Delete a file.
[code language=”java”]
private void deleteMyFile(String fileName) {
File dir = getFilesDir();
File file = new File(dir, fileName);
boolean deleted = file.delete();
if (deleted) {
displayText("File deleted.");
} else {
displayText("File not deleted.");
}
}
[/code]

Check if a file exist.
[code language=”java”]
private boolean fileExists() {
File dir = getFilesDir();
File file = new File(dir, fileName);
return file.exists();
}
[/code]

A complete demo Activity class for writing and reading from a file in Android
[code language=”java”]
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class FileStorageActivity extends Activity {
private static final String fileName = "my_note.txt";
private EditText etInputString;
private Button btnWrite;
private Button btnRead;
private Button btnDelete;
private TextView tvDisplay;

@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
getApplicationContext();
etInputString = (EditText) findViewById(R.id.et_input_string);
btnWrite = (Button) findViewById(R.id.btn_write);
btnRead = (Button) findViewById(R.id.btn_read);
btnDelete = (Button) findViewById(R.id.btn_delete);
tvDisplay = (TextView) findViewById(R.id.tv_display);

initButtonListeners();
}

private void initButtonListeners() {
btnWrite.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
if (!fileExists()) {
try {
String inputString = etInputString.getText().toString();
writeFile(inputString);
} catch (IOException e) {
errorNotification(e.getMessage());
}
} else {
displayText(fileName + " already exists!");
}
}
});

btnRead.setOnClickListener(new View.OnClickListener() {

public void onClick(View v) {
if (fileExists()) {
try {
String myString = readFile();
displayText(myString);
} catch (IOException e) {
errorNotification(e.getMessage());
}
} else {
displayText(fileName + " does not exist!");
}
}
});

btnDelete.setOnClickListener(new View.OnClickListener() {

public void onClick(View v) {
if (fileExists()) {
deleteMyFile(fileName);
} else {
displayText(fileName + " does not exist");
}
}
});
}

private void writeFile(String stringToSave) throws IOException {
FileOutputStream outStream = null;
try {
outStream = openFileOutput(fileName, Context.MODE_PRIVATE);
outStream.write(stringToSave.getBytes());
if (fileExists()) {
displayText("File saved.");
} else {
displayText("File not saved.");
}
} catch (Exception e) {
errorNotification(e.getMessage());
} finally {
outStream.close();
}
}

private String readFile() throws IOException {
FileInputStream inStream = null;
InputStreamReader myInputStreamReader = null;
BufferedReader myBufferedReader = null;
String retrievedString = "";
try {
inStream = openFileInput(fileName);
myInputStreamReader = new InputStreamReader(inStream);
myBufferedReader = new BufferedReader(myInputStreamReader);
String readLineString = myBufferedReader.readLine();
while (readLineString != null) {
retrievedString = retrievedString + readLineString;
readLineString = myBufferedReader.readLine();
}
} catch (IOException ioe) {
errorNotification(ioe.getMessage());
} finally {
myBufferedReader.close();
myInputStreamReader.close();
inStream.close();
}
return retrievedString;
}

private void deleteMyFile(String fileName) {
File dir = getFilesDir();
File file = new File(dir, fileName);
boolean deleted = file.delete();
if (deleted) {
displayText("File deleted.");
} else {
displayText("File not deleted.");
}
}

private boolean fileExists() {
File dir = getFilesDir();
File file = new File(dir, fileName);
return file.exists();
}

private void displayText(String stringName) {
tvDisplay = (TextView) findViewById(R.id.tv_display);
tvDisplay.setText(stringName);
}

private void errorNotification(String message) {
tvDisplay = (TextView) findViewById(R.id.tv_display);
tvDisplay.setTextColor(getResources().getColor(R.color.red));
tvDisplay.setText("ERROR: " + message);
}
}
[/code]

The layout file main.xml for the demo activity.
[code language=”xml”]
<?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" >

<EditText
android:id="@+id/et_input_string"
android:layout_width="fill_parent"
android:layout_height="200dp"
android:hint="Wite something here…"/>

<Button
android:id="@+id/btn_write"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Write" />

<Button
android:id="@+id/btn_read"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Read" />

<Button
android:id="@+id/btn_delete"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Delete" />

<TextView
android:id="@+id/tv_display"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textColor="@android:color/white"/>

</LinearLayout>
[/code]

Complete example in Github