var myExternalFile:File = File(getExternalFilesDir(filepath),fileName)
 try {
     val fileOutPutStream = FileOutputStream(myExternalFile)
     fileOutPutStream.write(fileContent.toByteArray())
     fileOutPutStream.close()
 } catch (e: IOException) {
     e.printStackTrace()
 }

var myExternalFile:File = File(getExternalFilesDir(filepath), fileName)
val filename = fileName.text.toString()
myExternalFile = File(getExternalFilesDir(filepath),filename) 
    var fileInputStream =FileInputStream(myExternalFile)
    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)
    }
    fileInputStream.close()

package example.javatpoint.com.kotlinexternalstoragereadwrite

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 android.os.Environment
import java.io.*

class MainActivity : AppCompatActivity() {
    private val filepath = "MyFileStorage"
    internal var myExternalFile: File?=null
    private val isExternalStorageReadOnly: Boolean get() {
        val extStorageState = Environment.getExternalStorageState()
        return if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(extStorageState)) {
                true
        } else {
                false
        }
    }
    private val isExternalStorageAvailable: Boolean get() {
        val extStorageState = Environment.getExternalStorageState()
        return if (Environment.MEDIA_MOUNTED.equals(extStorageState)) {
            true
        } else{
            false
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val fileName = findViewById(R.id.editTextFile) as EditText
        val fileData = findViewById(R.id.editTextData) as EditText
        val saveButton = findViewById(R.id.button_save) as Button
        val viewButton = findViewById(R.id.button_view) as Button

        saveButton.setOnClickListener(View.OnClickListener {
           myExternalFile = File(getExternalFilesDir(filepath), fileName.text.toString())
            try {
                val fileOutPutStream = FileOutputStream(myExternalFile)
                fileOutPutStream.write(fileData.text.toString().toByteArray())
                fileOutPutStream.close()
            } catch (e: IOException) {
                e.printStackTrace()
            }
            Toast.makeText(applicationContext,"data save",Toast.LENGTH_SHORT).show()
        })
        viewButton.setOnClickListener(View.OnClickListener {
           myExternalFile = File(getExternalFilesDir(filepath), fileName.text.toString())

           val filename = fileName.text.toString()
           myExternalFile = File(getExternalFilesDir(filepath),filename)
           if(filename.toString()!=null && filename.toString().trim()!=""){
               var fileInputStream =FileInputStream(myExternalFile)
               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)
               }
               fileInputStream.close()
               //Displaying data on EditText
               Toast.makeText(applicationContext,stringBuilder.toString(),Toast.LENGTH_SHORT).show()
           }
        })

        if (!isExternalStorageAvailable || isExternalStorageReadOnly) {
            saveButton.isEnabled = false
        }
    }
}