Read/Write String from/to a File in Android

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.

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;
}

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.

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();
}

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;
}

check the below code.

Reading from a file in the filesystem.

FileInputStream fis = null;
	try {
		
		fis = context.openFileInput(fileName);
		InputStreamReader isr = new InputStreamReader(fis);
		// READ STRING OF UNKNOWN LENGTH
		StringBuilder sb = new StringBuilder();
		char[] inputBuffer = new char[2048];
		int l;
		// FILL BUFFER WITH DATA
		while ((l = isr.read(inputBuffer)) != -1) {
			sb.append(inputBuffer, 0, l);
		}
		// CONVERT BYTES TO STRING
		String readString = sb.toString();
		fis.close();
	
	catch (Exception e) {
		
	} finally {
		if (fis != null) {
			fis = null;
		}
	}

below code is to write the file in to internal filesystem.

FileOutputStream fos = null;
	try {
		
		fos = context.openFileOutput(fileName, Context.MODE_PRIVATE);
		fos.write(stringdatatobestoredinfile.getBytes());
		fos.flush();
		fos.close();
				
	} catch (Exception e) {
		
	} finally {
		if (fos != null) {
			fos = null;
		}
	}

I think this will help you.

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();
        }
    }
}

The Kotlin way by using builtin Extension function on File

Write: yourFile.writeText(textFromEditText)
Read: yourFile.readText()

the first thing we need is the permissions in AndroidManifest.xml

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

so in an asyncTask Kotlin class, we treat the creation of the file

	import android.os.AsyncTask
	import android.os.Environment
	import android.util.Log
	import java.io.*
	class WriteFile: AsyncTask<String, Int, String>() {
		private val mFolder = "/MainFolder"
		lateinit var folder: File
		internal var writeThis = "string to cacheApp.txt"
		internal var cacheApptxt = "cacheApp.txt"
		override fun doInBackground(vararg writethis: String): String? {
			val received = writethis[0]
			if(received.isNotEmpty()){
				writeThis = received
			}
			folder = File(Environment.getExternalStorageDirectory(),"$mFolder/")
			if(!folder.exists()){
				folder.mkdir()
				val readME = File(folder, cacheApptxt)
				val file = File(readME.path)
				val out: BufferedWriter
				try {
					out = BufferedWriter(FileWriter(file, true), 1024)
					out.write(writeThis)
					out.newLine()
					out.close()
					Log.d("Output_Success", folder.path)
				} catch (e: Exception) {
					Log.d("Output_Exception", "$e")
				}
			}
			return folder.path

	}

		override fun onPostExecute(result: String) {
			super.onPostExecute(result)

			if(result.isNotEmpty()){
				//implement an interface or do something
				Log.d("onPostExecuteSuccess", result)
			}else{
				Log.d("onPostExecuteFailure", result)
			}
		}

	}

Of course if you are using Android above Api 23, you must handle the request to allow writing to device memory. Something like this

 	import android.Manifest
	import android.content.Context
	import android.content.pm.PackageManager
	import android.os.Build
	import androidx.appcompat.app.AppCompatActivity
	import androidx.core.app.ActivityCompat
	import androidx.core.content.ContextCompat

	class ReadandWrite {
		private val mREAD = 9
		private val mWRITE = 10
		private var readAndWrite: Boolean = false
		fun readAndwriteStorage(ctx: Context, atividade: AppCompatActivity): Boolean {
			if (Build.VERSION.SDK_INT < 23) {
				readAndWrite = true
			} else {
				val mRead = ContextCompat.checkSelfPermission(ctx, Manifest.permission.READ_EXTERNAL_STORAGE)
				val mWrite = ContextCompat.checkSelfPermission(ctx, Manifest.permission.WRITE_EXTERNAL_STORAGE)

				if (mRead != PackageManager.PERMISSION_GRANTED) {
					ActivityCompat.requestPermissions(atividade, arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE), mREAD)
				} else {
					readAndWrite = true
				}

				if (mWrite != PackageManager.PERMISSION_GRANTED) {
					ActivityCompat.requestPermissions(atividade, arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), mWRITE)
				} else {
					readAndWrite = true
				}
			}
			return readAndWrite
		}
	}

then in an activity, execute the call.

  var pathToFileCreated = ""
    val anRW = ReadandWrite().readAndwriteStorage(this,this)
    if(anRW){
        pathToFileCreated =  WriteFile().execute("onTaskComplete").get()
        Log.d("pathToFileCreated",pathToFileCreated)
    }

Kotlin

class FileReadWriteService {

    private var context:Context? = ContextHolder.instance.appContext

    fun writeFileOnInternalStorage(fileKey: String, sBody: String) {
        val file = File(context?.filesDir, "files")
        try {
            if (!file.exists()) {
                file.mkdir()
            }
            val fileToWrite = File(file, fileKey)
            val writer = FileWriter(fileToWrite)
            writer.append(sBody)
            writer.flush()
            writer.close()
        } catch (e: Exception) {
            Logger.e(classTag, e)
        }
    }

    fun readFileOnInternalStorage(fileKey: String): String {
        val file = File(context?.filesDir, "files")
        var ret = ""
        try {
            if (!file.exists()) {
                return ret
            }
            val fileToRead = File(file, fileKey)
            val reader = FileReader(fileToRead)
            ret = reader.readText()
            reader.close()
        } catch (e: Exception) {
            Logger.e(classTag, e)
        }
        return ret
    }
}

We can use this code to write String to a file

public static void writeTextToFile(final String filename, final String data) {
    File file = new File(filename);
    try {
        FileOutputStream stream = new FileOutputStream(file);
        stream.write(data.getBytes());
        stream.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Then in the Main code, we use this, for example

writeTextToFile(getExternalFilesDir("/").getAbsolutePath() + "/output.txt", "my-example-text");

After that, check the file at Android/data/<package-name>/files.

The easiest way to append to a text file in kotlin:

val directory = File(context.filesDir, "LogsToSendToNextMunich").apply { 
    mkdirs() 
}
val file = File(directory,"Logs.txt")
file.appendText("You new text")

If you want to just write to the file:

yourFile.writeText("You new text")

writing anything to the files, using bytes:

FileOutputStream(file).use {
    it.write("Some text for example".encodeToByteArray()) 
}