Read, Write and Delete File in Internal Storage

Create Project

Create new project in Android Studio with steps as below:

Step 1: Input Project Name and Select Project Location

Step 2: Select SDK for Android App

Step 3: Select Default Activity for App

Step 4: Finish create project

Add Strings

Open res\values\strings.xml file and add new string as below:

<resources>
    <string name="app_name">Learn Android with Real Apps</string>
    <string name="folder_name">Folder Name</string>
    <string name="file_name">File Name</string>
    <string name="content">Content</string>
    <string name="write_file">Write File</string>
    <string name="read_file">Read File</string>
    <string name="delete_file">Delete File</string>
    <string name="done">Done</string>
</resources>

Main Activity Layout

Open res\layout\activity_main.xml file and create layout as below:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="#ffffff"
    android:orientation="vertical"
    tools:ignore="HardcodedText">

    <EditText
        android:id="@+id/editTextFolderName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/folder_name"
        android:inputType="textPersonName" />

    <EditText
        android:id="@+id/editTextFileName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/file_name"
        android:inputType="textPersonName" />

    <EditText
        android:id="@+id/editTextContent"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:hint="@string/content"
        android:inputType="textMultiLine" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal">

        <Button
            android:id="@+id/buttonWriteFile"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/write_file" />

        <Button
            android:id="@+id/buttonReadFile"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/read_file" />

        <Button
            android:id="@+id/buttonDeleteFile"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="@string/delete_file" />
    </LinearLayout>

</LinearLayout>

Main Activity Class

Add code to MainActivity.java file in android.demo.learnandroidwithrealapps package as below:

package android.demo.learnandroidwithrealapps;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileReader;

public class MainActivity extends AppCompatActivity {

    private EditText editTextFileName, editTextFolderName, editTextContent;
    private Button buttonDeleteFile, buttonWriteFile, buttonReadFile;

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

    private void initView() {
        editTextFileName = findViewById(R.id.editTextFileName);
        editTextFolderName = findViewById(R.id.editTextFolderName);
        editTextContent = findViewById(R.id.editTextContent);
        buttonReadFile = findViewById(R.id.buttonReadFile);
        buttonReadFile.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                buttonReadFile_onClick(view);
            }
        });
        buttonWriteFile = findViewById(R.id.buttonWriteFile);
        buttonWriteFile.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                buttonWriteFile_onClick(view);
            }
        });
        buttonDeleteFile = findViewById(R.id.buttonDeleteFile);
        buttonDeleteFile.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                buttonDeleteFile_onClick(view);
            }
        });
    }

    private void buttonReadFile_onClick(View view) {
        try {
            StringBuilder result = new StringBuilder();
            String line;
            String folder = getApplication().getFilesDir().getAbsolutePath() + File.separator + editTextFolderName.getText().toString();
            File subFolder = new File(folder);
            BufferedReader bufferedReader = new BufferedReader(new FileReader(new File(folder, editTextFileName.getText().toString())));
            while ((line = bufferedReader.readLine()) != null) {
                result.append(line);
            }
            editTextContent.setText(result.toString());
        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();
        }
    }

    private void buttonWriteFile_onClick(View view) {
        try {
            String folder = getApplication().getFilesDir().getAbsolutePath() + File.separator + editTextFolderName.getText().toString();
            File subFolder = new File(folder);
            if (!subFolder.exists()) {
                subFolder.mkdirs();
            }
            FileOutputStream outputStream = new FileOutputStream(new File(subFolder, editTextFileName.getText().toString()));
            outputStream.write(editTextContent.getText().toString().getBytes());
            outputStream.close();
            Toast.makeText(getApplicationContext(), getString(R.string.done), Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();
        }
    }

    private void buttonDeleteFile_onClick(View view) {
        try {
            String folder = getApplication().getFilesDir().getAbsolutePath() + File.separator + editTextFolderName.getText().toString();
            File subFolder = new File(folder);
            File file = new File(folder, editTextFileName.getText().toString());
            if(file.exists()) {
                file.delete();
            }
            Toast.makeText(getApplicationContext(), getString(R.string.done), Toast.LENGTH_LONG).show();
        } catch (Exception e) {
            Toast.makeText(getApplicationContext(), e.getMessage(), Toast.LENGTH_LONG).show();
        }
    }
}

Structure of Project

Run App

Write A File To A Folder

File and Folder in Emulator

Read A File To A Folder

Delete A File To A Folder

Folder After Delete in Emulator