Retrieve contents of file on SD card. Android

public void getFile(){
//Get the text file
        File file = new File(newFolder,"MyTest.txt");

//Read text from file
        StringBuilder text = new StringBuilder();

        try {
            BufferedReader br = new BufferedReader(new FileReader(file));
            String line;

            while ((line = br.readLine()) != null) {
                text.append(line);
                text.append('\n');
            }
            br.close();
        }
        catch (IOException e) {
            Log.i("TAG","ERROR." + e);
        }

//Find the view by its id
        TextView tv = (TextView)findViewById(R.id.showFile);

//Set the text
        tv.setText(text.toString());
    }

Android. Create folder on SD card and write data

This will create a folder called TestFolder in /storage/emulated/0/ and write
to a text file called MyTest.txt in that folder.

File newFolder;//path to folder
File file;//path to file

public void writeData() {
createFolderIfNoneExists();

FileWriter writer = null;
try {
writer = new FileWriter(file);
// Writes the content to the file
writer.write("This\n is\n an\n example\n");
writer.flush();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}

public void createFolderIfNoneExists(){
try {
newFolder = new File(Environment.getExternalStorageDirectory(), "TestFolder");
if (!newFolder.exists()) {
newFolder.mkdir();
}
try {
file = new File(newFolder, "MyTest" + ".txt");
file.createNewFile();
} catch (Exception ex) {
Log.i("TAG", "Exception: " + ex);
}
} catch (Exception e) {
Log.i("TAG", "Exception 2: " + e);
}
}

To view the contents of the file you will need a reference to the folders path (The ‘folder’ variable in the above code) and the name of the file.
then use this code:
Retrieve file from SD card

Check if you can Read or write to SD Card android

The following method will check and see what read and write options are available
before writing to the SD card.

public void writeTocard(){
    Log.i("TAG", "writeTocard started");
    if (Environment.MEDIA_MOUNTED.equals(state)) {
        // We can read and write the media
        Log.i("TAG", "We can read and write to card");
        mExternalStorageAvailable = mExternalStorageWriteable = true;
    } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {
        // We can only read the media
        Log.i("TAG", "We can only read to card");
        mExternalStorageAvailable = true;
        mExternalStorageWriteable = false;
    } else {
        // Something else is wrong. It may be one of many other states, but all we need
        //  to know is we can neither read nor write
        Log.i("TAG", "We can NOT read or write to card");
        mExternalStorageAvailable = mExternalStorageWriteable = false;
    }
}

Install Stetho to view SQLite and local files on android device.

Create java file MyApplication

import android.app.Application;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;

import com.facebook.stetho.Stetho;

public class MyApplication extends Application {

public void onCreate() {
//Log.i("TAG","MyApplication started");

super.onCreate();
//Stetho.initializeWithDefaults(this);

// Create an InitializerBuilder
Stetho.InitializerBuilder initializerBuilder =
Stetho.newInitializerBuilder(this);

// Enable Chrome DevTools
initializerBuilder.enableWebKitInspector(
Stetho.defaultInspectorModulesProvider(this)
);

// Enable command line interface
initializerBuilder.enableDumpapp(
Stetho.defaultDumperPluginsProvider(this)
);

// Use the InitializerBuilder to generate an Initializer
Stetho.Initializer initializer = initializerBuilder.build();

// Initialize Stetho with the Initializer
Stetho.initialize(initializer);

}
}

In the androidManifest file add:

<application
    android:name=".MyApplication">

In the build.gradle(Module.app) add the following to the dependencies:

//Stetho is used to see SQLite database in Chrome. Go to Chrome://inspect
// Stetho core
compile 'com.facebook.stetho:stetho:1.3.1'
//Optional network helper
compile 'com.facebook.stetho:stetho-okhttp:1.3.1'
compile 'com.facebook.stetho:stetho-js-rhino:1.4.2'