Read/Write String from/to a File in Android

233

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.

This question is tagged with java android string file-io

~ Asked on 2013-01-17 10:20:02

The Best Answer is


355

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("\n").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;
}

~ Answered on 2013-01-17 10:39:53


200

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.

~ Answered on 2014-02-28 10:48:30


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