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Android Internal Storage Tutorial

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1- Android Internal Storage

Android Internal Storage: A place to store private data of each application, this data is stored and used for own application. Other applications can not access it. Normally when the application is removed from Android devices, the associated data file is also removed.
Another feature when you work with files in Internal Storage, you can only work with a simple file name, can not work with a file name has the path.

Open file to write:

// Is a simple file name.
// Note!! Do not allow the path.
String simpleFileName ="note.txt";


// Open Stream to write file.
FileOutputStream out = openFileOutput(simpleFileName, MODE_PRIVATE);
You have four option for creating mode:
Mode Description
MODE_PRIVATE File creation mode: the default mode, where the created file can only be accessed by the calling application (or all applications sharing the same user ID).
MODE_APPEND Mode data appended to the file if it already exists.
MODE_ENABLE_WRITE_AHEAD_LOGGING  
MODE_WORLD_READABLE These modes are very dangerous, it's like a security hole in Android, best not to use, you can use alternative techniques such as:
  • ContentProvider
  • BroadcastReceiver
  • Service
MODE_WORLD_WRITEABLE
MODE_MULTI_PROCESS This mode allows multiple processes can be writen to the file. However, it is recommended that you should not use this mode because it does not work on some versions of Android. You can use other techniques:
  • ContentProvider

Open file to read data:

// Is a simple file name.
// Note!! Do not allow the path.
String simpleFileName = "note.txt";

// Open stream to read file.
FileInputStream in = this.openFileInput(simpleFileName);

2- Reading and writing data to Internal Storage example

Now you can make an example of writing data to files stored in Internal Storage, and read data from this file.
Create a project named InternalStorageDemo.
  • File > New > New Project > Empty Activity
    • Name: InternalStorageDemo
    • Package name: org.o7planning.internalstoragedemo
    • Language: Java
The application interface:
The interface of this application is very simple, if you are interested in the steps to create it, see the appendix at the end of the article.
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editText"
        android:layout_width="0dp"
        android:layout_height="122dp"
        android:layout_marginStart="21dp"
        android:layout_marginLeft="21dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:ems="10"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button_save"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="44dp"
        android:text="Save to File"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editText" />

    <TextView
        android:id="@+id/textView"
        android:layout_width="0dp"
        android:layout_height="91dp"
        android:layout_marginStart="29dp"
        android:layout_marginLeft="29dp"
        android:layout_marginTop="29dp"
        android:layout_marginEnd="21dp"
        android:layout_marginRight="21dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button_save" />

    <Button
        android:id="@+id/button_read"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="38dp"
        android:text="Read File"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView" />
</androidx.constraintlayout.widget.ConstraintLayout>
MainActivity.java
package org.o7planning.internalstoragedemo;

import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;

public class MainActivity extends AppCompatActivity {

    private Button saveButton;
    private Button readButton;

    private TextView textView;
    private EditText editText;

    // Is a simple file name.
    // Note!! Do not allow the path.
    private String simpleFileName = "note.txt";

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

        this.saveButton = (Button) this.findViewById(R.id.button_save);
        this.readButton = (Button) this.findViewById(R.id.button_read);
        this.textView = (TextView) this.findViewById(R.id.textView);
        this.editText = (EditText) this.findViewById(R.id.editText);

        this.saveButton.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                saveData();
            }
        });

        this.readButton.setOnClickListener(new Button.OnClickListener() {

            @Override
            public void onClick(View v) {
                readData();
            }
        });
    }


    private void saveData() {
        String data = this.editText.getText().toString();
        try {
            // Open Stream to write file.
            FileOutputStream out = this.openFileOutput(simpleFileName, MODE_PRIVATE);
            // Ghi dữ liệu.
            out.write(data.getBytes());
            out.close();
            Toast.makeText(this,"File saved!",Toast.LENGTH_SHORT).show();
        } catch (Exception e) {
            Toast.makeText(this,"Error:"+ e.getMessage(),Toast.LENGTH_SHORT).show();
        }
    }

    private void readData() {
        try {
            // Open stream to read file.
            FileInputStream in = this.openFileInput(simpleFileName);

            BufferedReader br= new BufferedReader(new InputStreamReader(in));

            StringBuilder sb= new StringBuilder();
            String s= null;
            while((s= br.readLine())!= null)  {
                sb.append(s).append("\n");
            }
            this.textView.setText(sb.toString());

        } catch (Exception e) {
            Toast.makeText(this,"Error:"+ e.getMessage(),Toast.LENGTH_SHORT).show();
        }
    }

}
Use the "Android Device Manager" you can see the file is created.
See more about "Device File Explorer":

3- Appendix: Interface design

Steps to design the interface of the application in this article:
Add Button "Save to File":
Add a TextView:
Add Button "Read File":
Set ID, Text for components on the interface:

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