How to add numbers to the end of a file?

Question

I am trying to write a text file to the external storage, I am wondering how to append to the filename so that I can store unique files and not overwrite the past ones.

As well, I see the file in the file explorer on android studio, but can't find it on my phone, the same thing happens when I use an emulator, I don't see it in the file explorer but can verify it exists when using the device explorer.

My code:

import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    Button btnSave, btnLoad;
    EditText etInput;
    TextView tvLoad;
    String fileName = "";
    String filePath = "";
    String fileContent = "";

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

        btnSave = findViewById(R.id.buttonSave);
        btnLoad = findViewById(R.id.buttonLoad);
        etInput = findViewById(R.id.etInput);
        tvLoad = findViewById(R.id.tvLoad);

        fileName = "myFile.txt";
        filePath = "myFileDir";

        if(!isExternalStorageAvailableForRW()){
            btnSave.setEnabled(false);
        }
        btnSave.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                tvLoad.setText("");
                fileContent = etInput.getText().toString().trim();
                if(!fileContent.equals("")){
                    File myExternalFile = new File(getExternalFilesDir(filePath), fileName);
                    FileOutputStream fos = null;
                    try {
                        fos = new FileOutputStream(myExternalFile);
                        fos.write(fileContent.getBytes());
                    } catch (FileNotFoundException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                    etInput.setText("");
                    Toast.makeText(MainActivity.this,"File Saved, check dir", Toast.LENGTH_SHORT).show();
                }
                else{
                    Toast.makeText(MainActivity.this,"Textfield empty", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }

    private boolean isExternalStorageAvailableForRW() {
        String extStorageState = Environment.getExternalStorageState();
        if(extStorageState.equals(Environment.MEDIA_MOUNTED)){
            return true;
        }
        return false;
    }
}

Answer 1

For

Java 7+

For a one-time task, the Files class makes this easy:

try {
    Files.write(Paths.get("filePath"), "the text".getBytes(), StandardOpenOption.APPEND);
}catch (IOException e) {
    //exception handling left as an exercise for the reader
}

The above approach will throw a

NoSuchFileException

if the file does not already exist. It also does not append a newline automatically (which you often want when appending to a text file). Another approach is to pass both CREATE and APPEND options, which will create the file first if it doesn't already exist:

private void write(final String s) throws IOException {
    Files.writeString(
        Path.of(System.getProperty("java.io.tmpdir"), "filePath"),
        s + System.lineSeparator(),
        CREATE, APPEND
    );
}

The Source