Kotlin Android Read and Write Internal Storage

Android Internal Storage is the device memory in which we store the files. The file stored in the internal storage is private in default, and only the same application accesses it. They cannot be accessed from outside the application.

To read and write the data from (into) the file, Android provides openFileInput() and openFileOutput() methods respectively.

When the users uninstall its application from the device, its internal storage file will also be removed.

Write to File in Internal Storage

To write the file in internal storage of device, java.io package offers openFileOutput() method which returns the instance of FileOutputStream class. To write the data into the file call the FileOutputStream .write() method.

val file:String = fileName.text.toString()
val data:String = fileData.text.toString()
val fileOutputStream:FileOutputStream
try {
    fileOutputStream = openFileOutput(file, Context.MODE_PRIVATE)
    fileOutputStream.write(data.toByteArray())
}catch (e: Exception){
    e.printStackTrace()
}

Read File content from Internal Storage

To read the file from the internal storage of device, java.io package offers openFileInput() method which returns the instance of FileInputStream class. To read the data from file call the BufferedReader().readLine()

var fileInputStream: FileInputStream? = null
fileInputStream = openFileInput(filename)
var inputStreamReader: InputStreamReader = InputStreamReader(fileInputStream)
val bufferedReader: BufferedReader = BufferedReader(inputStreamReader)
val stringBuilder: StringBuilder = StringBuilder()
var text: String? = null
while ({ text = bufferedReader.readLine(); text }() != null) {
    stringBuilder.append(text)
}
//Displaying data on EditText
fileData.setText(stringBuilder.toString()).toString()

Kotlin Android Read and Write Internal Storage Example

In this example, we will write the data to file inside the internal storage and read the same file content from internal storage.

activity_main.xml

Add the following code in the activity_main.xml file. In this file, add two EditText for input file name, file content and two Button for saving and view file content.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 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="example.javatpoint.com.kotlininternalstoragereadwrite.MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="31dp"
        android:layout_marginStart="31dp"
        android:layout_marginTop="117dp"
        android:text="File Name"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>

    <EditText
        android:id="@+id/editFile"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView"
        android:layout_alignBottom="@+id/textView"
        android:layout_alignLeft="@+id/btnSave"
        android:layout_alignStart="@+id/btnSave"
        android:layout_marginLeft="31dp"
        android:layout_marginStart="31dp"
        android:ems="10"
        android:paddingLeft="10dp"
        android:inputType="textPersonName"
        android:hint="file name" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/textView"
        android:layout_alignRight="@+id/textView"
        android:layout_below="@+id/textView"
        android:layout_marginTop="67dp"
        android:text="File Data"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Medium"/>

    <EditText
        android:id="@+id/editData"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/textView2"
        android:layout_alignBottom="@+id/textView2"
        android:layout_alignLeft="@+id/editFile"
        android:layout_alignStart="@+id/editFile"
        android:ems="10"
        android:lines="5"
        android:hint="data" />

    <Button
        android:id="@+id/btnSave"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/textView2"
        android:layout_alignParentBottom="true"
        android:layout_alignStart="@+id/textView2"
        android:layout_marginBottom="53dp"
        android:layout_marginLeft="49dp"
        android:layout_marginStart="49dp"
        android:text="Save" />

    <Button
        android:id="@+id/btnView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignEnd="@+id/editData"
        android:layout_alignRight="@+id/editData"
        android:layout_alignTop="@+id/btnSave"
        android:layout_marginEnd="33dp"
        android:layout_marginRight="33dp"
        android:text="View" />
</RelativeLayout>

MainActivity.kt

Add the following code in the MainActivity.kt class. In this class, we are saving the file name and data inside internal storage by clicking the save button and retrieving the file content by clicking view button.

package example.javatpoint.com.kotlininternalstoragereadwrite

import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.view.View
import android.widget.Button
import android.widget.EditText
import android.widget.Toast
import java.io.*


class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val fileName = findViewById<EditText>(R.id.editFile)
        val fileData = findViewById<EditText>(R.id.editData)

        val btnSave = findViewById<Button>(R.id.btnSave)
        val btnView = findViewById<Button>(R.id.btnView)

        btnSave.setOnClickListener(View.OnClickListener {
            val file:String = fileName.text.toString()
            val data:String = fileData.text.toString()
            val fileOutputStream:FileOutputStream
            try {
                fileOutputStream = openFileOutput(file, Context.MODE_PRIVATE)
                fileOutputStream.write(data.toByteArray())
            } catch (e: FileNotFoundException){
                e.printStackTrace()
            }catch (e: NumberFormatException){
                e.printStackTrace()
            }catch (e: IOException){
                e.printStackTrace()
            }catch (e: Exception){
                e.printStackTrace()
            }
            Toast.makeText(applicationContext,"data save",Toast.LENGTH_LONG).show()
            fileName.text.clear()
            fileData.text.clear()
        })

        btnView.setOnClickListener(View.OnClickListener {
                val filename = fileName.text.toString()
                if(filename.toString()!=null && filename.toString().trim()!=""){
                   var fileInputStream: FileInputStream? = null
                   fileInputStream = openFileInput(filename)
                   var inputStreamReader: InputStreamReader = InputStreamReader(fileInputStream)
                   val bufferedReader: BufferedReader = BufferedReader(inputStreamReader)
                   val stringBuilder: StringBuilder = StringBuilder()
                   var text: String? = null
                   while ({ text = bufferedReader.readLine(); text }() != null) {
                       stringBuilder.append(text)
                   }
                   //Displaying data on EditText
                   fileData.setText(stringBuilder.toString()).toString()
               }else{
                   Toast.makeText(applicationContext,"file name cannot be blank",Toast.LENGTH_LONG).show()
               }
        })

    }
}

Output: