FileUtil.java

import android.os.Environment;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;


public class FileUtil {

    private final static String SAVE_DIRECTORY = "MyAppSaveDirectory";

    public static boolean writeToFile(String str, String fileName) {

        File saveDirectory = getSaveDirectory();
        File file = new File(saveDirectory, fileName);

        BufferedWriter bw = null;
        try{
            bw = new BufferedWriter(new FileWriter(file));

            bw.write(str);
            bw.newLine();

            bw.flush();
            bw.close();
            return true;
        }catch (IOException e) {
            return false;
        }
    }

    public static String readFromFile(String fileName) {
        File saveDirectory = getSaveDirectory();
        File file = new File(saveDirectory, fileName);

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

            String tmp = null;
            while((tmp = br.readLine()) != null) {
                readData += tmp + "\n";
            }

            return readData;
        } catch (IOException e) {
            return null;
        }
    }

    public static File getSaveDirectory() {
        String root = Environment.getExternalStorageDirectory().toString();
        File directory = new File(root, SAVE_DIRECTORY);
        if(!directory.exists()) {
            directory.mkdirs();
        }
        return directory;
    }

}