Android External Storage

Like internal storage, we are able to save or read data from the device external memory such as sdcard. FileInputStream and FileOutputStream classes are used to read and write data into the file.
activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"  
    xmlns:tools="http://schemas.android.com/tools"  
    android:layout_width="match_parent"  
    android:layout_height="match_parent"  
    tools:context=".MainActivity" >  
  
    <EditText  
        android:id="@+id/editText1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignParentRight="true"  
        android:layout_alignParentTop="true"  
        android:layout_marginRight="20dp"  
        android:layout_marginTop="24dp"  
        android:ems="10" >  
  
        <requestFocus />  
    </EditText>  
  
    <EditText  
        android:id="@+id/editText2"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignRight="@+id/editText1"  
        android:layout_below="@+id/editText1"  
        android:layout_marginTop="24dp"  
        android:ems="10" />  
  
    <TextView  
        android:id="@+id/textView1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignBaseline="@+id/editText1"  
        android:layout_alignBottom="@+id/editText1"  
        android:layout_alignParentLeft="true"  
        android:text="File Name:" />  
  
    <TextView  
        android:id="@+id/textView2"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignBaseline="@+id/editText2"  
        android:layout_alignBottom="@+id/editText2"  
        android:layout_alignParentLeft="true"  
        android:text="Data:" />  
  
    <Button  
        android:id="@+id/button1"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignLeft="@+id/editText2"  
        android:layout_below="@+id/editText2"  
        android:layout_marginLeft="70dp"  
        android:layout_marginTop="16dp"  
        android:text="save" />  
  
    <Button  
        android:id="@+id/button2"  
        android:layout_width="wrap_content"  
        android:layout_height="wrap_content"  
        android:layout_alignBaseline="@+id/button1"  
        android:layout_alignBottom="@+id/button1"  
        android:layout_toRightOf="@+id/button1"  
        android:text="read" />  
  
</RelativeLayout> 

Provide permission for the external storage
You need to provide the WRITE_EXTERNAL_STORAGE permission.
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
Activity_Manifest.xml

<?xml version="1.0" encoding="utf-8"?>  
<manifest   
  
xmlns:android="http://schemas.android.com/apk/res/android"  
    package="com.example.externalstorage"  
    android:versionCode="1"  
    android:versionName="1.0" >  
  
    <uses-sdk  
        android:minSdkVersion="8"  
        android:targetSdkVersion="16" />  
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>  
  
    <application  
        android:allowBackup="true"  
        android:icon="@drawable/ic_launcher"  
        android:label="@string/app_name"  
        android:theme="@style/AppTheme" >  
        <activity  
            android:name="com.example.externalstorage.MainActivity"  
            android:label="@string/app_name" >  
            <intent-filter>  
                <action android:name="android.intent.action.MAIN" />  
  
                <category android:name="android.intent.category.LAUNCHER" />  
            </intent-filter>  
        </activity>  
    </application>  
  
</manifest>    

MainActivity.java

import java.io.BufferedReader;  
import java.io.File;  
import java.io.FileInputStream;  
import java.io.FileNotFoundException;  
import java.io.FileOutputStream;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.io.OutputStreamWriter;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.content.Context;  
import android.view.Menu;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Button;  
import android.widget.EditText;  
import android.widget.Toast;  
  
public class MainActivity extends Activity {  
    EditText editTextFileName,editTextData;  
    Button saveButton,readButton;  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
          
        editTextFileName=(EditText)findViewById(R.id.editText1);  
        editTextData=(EditText)findViewById(R.id.editText2);  
        saveButton=(Button)findViewById(R.id.button1);  
        readButton=(Button)findViewById(R.id.button2);  
          
        //Performing action on save button  
        saveButton.setOnClickListener(new OnClickListener(){  
  
            @Override  
            public void onClick(View arg0) {  
                String filename=editTextFileName.getText().toString();  
                String data=editTextData.getText().toString();  
                  
                FileOutputStream fos;  
                   try {  
                       File myFile = new File("/sdcard/"+filename);  
                        myFile.createNewFile();  
                        FileOutputStream fOut = new   
  
FileOutputStream(myFile);  
                        OutputStreamWriter myOutWriter = new   
  
OutputStreamWriter(fOut);  
                        myOutWriter.append(data);  
                        myOutWriter.close();  
                        fOut.close();  
                     
            Toast.makeText(getApplicationContext(),filename + "   
  
saved",Toast.LENGTH_LONG).show();  
                      
                     
                   } catch (FileNotFoundException e) {e.printStackTrace();}  
                   catch (IOException e) {e.printStackTrace();}  
                  
            }  
              
        });  
  
        //Performing action on Read Button  
        readButton.setOnClickListener(new OnClickListener(){  
  
            @Override  
            public void onClick(View arg0) {  
                String filename=editTextFileName.getText().toString();  
                StringBuffer stringBuffer = new StringBuffer();    
                String aDataRow = "";  
                String aBuffer = "";  
                try {  
                    File myFile = new File("/sdcard/"+filename);  
                    FileInputStream fIn = new FileInputStream(myFile);  
                    BufferedReader myReader = new BufferedReader(  
                            new InputStreamReader(fIn));  
                      
                    while ((aDataRow = myReader.readLine()) != null) {  
                        aBuffer += aDataRow + "\n";  
                    }  
                    myReader.close();  
                      
                } catch (IOException e) {  
                    e.printStackTrace();  
                }  
                Toast.makeText(getApplicationContext  
  
(),aBuffer,Toast.LENGTH_LONG).show();  
                  
            }  
              
        });  
    }  
  
    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        // Inflate the menu; this adds items to the action bar if it is present.  
        getMenuInflater().inflate(R.menu.activity_main, menu);  
        return true;  
    }  
  
}