How to Read/Write String from a File in Android

Question

I want to save a file to the internal storage by getting the text inputted from EditText. Then I want the same file to return the inputted text in String form and save it to another String which is to be used later.

Here's the code:

package com.omm.easybalancerecharge;


import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.telephony.TelephonyManager;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        final EditText num = (EditText) findViewById(R.id.sNum);
        Button ch = (Button) findViewById(R.id.rButton);
        TelephonyManager operator = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
        String opname = operator.getNetworkOperatorName();
        TextView status = (TextView) findViewById(R.id.setStatus);
        final EditText ID = (EditText) findViewById(R.id.IQID);
        Button save = (Button) findViewById(R.id.sButton);

        final String myID = ""; //When Reading The File Back, I Need To Store It In This String For Later Use

        save.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                //Get Text From EditText "ID" And Save It To Internal Memory
            }
        });
        if (opname.contentEquals("zain SA")) {
            status.setText("Your Network Is: " + opname);
        } else {
            status.setText("No Network");
        }
        ch.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub

                //Read From The Saved File Here And Append It To String "myID"


                String hash = Uri.encode("#");
                Intent intent = new Intent(Intent.ACTION_CALL);
                intent.setData(Uri.parse("tel:*141*" + /*Use The String With Data Retrieved Here*/ num.getText()
                        + hash));
                startActivity(intent);
            }
        });
    }

I have included comments to help you further analyze my points as to where I want the operations to be done/variables to be used.

Answer 1

To append an existing file.

  File file = new File(persistPath);
  BufferedWriter out = new BufferedWriter(new FileWriter(file, true), 1024);
  out.write(str);
  out.newLine();
  out.close(); 

Answer 2

Just a a bit modifications on reading string from a file method for more performance

private String readFromFile(Context context, String fileName) {
    if (context == null) {
        return null;
    }

    String ret = "";

    try {
        InputStream inputStream = context.openFileInput(fileName);

        if ( inputStream != null ) {
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);               

            int size = inputStream.available();
            char[] buffer = new char[size];

            inputStreamReader.read(buffer);

            inputStream.close();
            ret = new String(buffer);
        }
    }catch (Exception e) {
        e.printStackTrace();
    }

    return ret;
}

Answer 3

I'm a bit of a beginner and struggled getting this to work today.

Below is the class that I ended up with. It works but I was wondering how imperfect my solution is. Anyway, I was hoping some of you more experienced folk might be willing to have a look at my IO class and give me some tips. Cheers!

public class HighScore {
    File data = new File(Environment.getExternalStorageDirectory().getAbsolutePath() + File.separator);
    File file = new File(data, "highscore.txt");
    private int highScore = 0;

    public int readHighScore() {
        try {
            BufferedReader br = new BufferedReader(new FileReader(file));
            try {
                highScore = Integer.parseInt(br.readLine());
                br.close();
            } catch (NumberFormatException | IOException e) {
                e.printStackTrace();
            }
        } catch (FileNotFoundException e) {
            try {
                file.createNewFile();
            } catch (IOException ioe) {
                ioe.printStackTrace();
            }
            e.printStackTrace();
        }
        return highScore;
    }

    public void writeHighScore(int highestScore) {
        try {
            BufferedWriter bw = new BufferedWriter(new FileWriter(file));
            bw.write(String.valueOf(highestScore));
            bw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Answer 4

Hope this might be useful to you.

Write File:

private void writeToFile(String data,Context context) {
    try {
        OutputStreamWriter outputStreamWriter = new OutputStreamWriter(context.openFileOutput("config.txt", Context.MODE_PRIVATE));
        outputStreamWriter.write(data);
        outputStreamWriter.close();
    }
    catch (IOException e) {
        Log.e("Exception", "File write failed: " + e.toString());
    } 
}

Read File:

private String readFromFile(Context context) {

    String ret = "";

    try {
        InputStream inputStream = context.openFileInput("config.txt");

        if ( inputStream != null ) {
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream);
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String receiveString = "";
            StringBuilder stringBuilder = new StringBuilder();

            while ( (receiveString = bufferedReader.readLine()) != null ) {
                stringBuilder.append(receiveString);
            }

            inputStream.close();
            ret = stringBuilder.toString();
        }
    }
    catch (FileNotFoundException e) {
        Log.e("login activity", "File not found: " + e.toString());
    } catch (IOException e) {
        Log.e("login activity", "Can not read file: " + e.toString());
    }

    return ret;
}

Answer 5

public static void writeStringAsFile(final String fileContents, String fileName) {
    Context context = App.instance.getApplicationContext();
    try {
        FileWriter out = new FileWriter(new File(context.getFilesDir(), fileName));
        out.write(fileContents);
        out.close();
    } catch (IOException e) {
        Logger.logError(TAG, e);
    }
}

public static String readFileAsString(String fileName) {
    Context context = App.instance.getApplicationContext();
    StringBuilder stringBuilder = new StringBuilder();
    String line;
    BufferedReader in = null;

    try {
        in = new BufferedReader(new FileReader(new File(context.getFilesDir(), fileName)));
        while ((line = in.readLine()) != null) stringBuilder.append(line);

    } catch (FileNotFoundException e) {
        Logger.logError(TAG, e);
    } catch (IOException e) {
        Logger.logError(TAG, e);
    } 

    return stringBuilder.toString();
}

Answer 6

For those looking for a general strategy for reading and writing a string to file:

First, get a file object

You'll need the storage path. For the internal storage, use:

File path = context.getFilesDir();

For the external storage (SD card), use:

File path = context.getExternalFilesDir(null);

Then create your file object:

File file = new File(path, "my-file-name.txt");

Write a string to the file

FileOutputStream stream = new FileOutputStream(file);
try {
    stream.write("text-to-write".getBytes());
} finally {
    stream.close();
}

Or with Google Guava

String contents = Files.toString(file, StandardCharsets.UTF_8);

Read the file to a string

int length = (int) file.length();

byte[] bytes = new byte[length];

FileInputStream in = new FileInputStream(file);
try {
    in.read(bytes);
} finally {
    in.close();
}

String contents = new String(bytes);   

Or if you are using Google Guava

String contents = Files.toString(file,"UTF-8");

For completeness I'll mention

String contents = new Scanner(file).useDelimiter("\\A").next();

which requires no libraries, but benchmarks 50% - 400% slower than the other options (in various tests on my Nexus 5).

Notes

For each of these strategies, you'll be asked to catch an IOException.

The default character encoding on Android is UTF-8.

If you are using external storage, you'll need to add to your manifest either:

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

or

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

Write permission implies read permission, so you don't need both.