Useful IO functions

import java.io.*;

public class Useful {

    public static void listFolderRec(File folder, String prefix) {
        File [] files = folder.listFiles();
        for(File f : files) {
            System.out.println(prefix + f.getName());
                if(f.isDirectory()) {
                    listFolderRec(f, prefix + "\t");
                }
            f
        }
    }

    public static void emptyDirectory(File folder){
        File [] files = folder.listFiles();
        for(File f : files) {
            if(f.isFile()) {
                System.out.println("Deleting file: " + f.getName());
                f.delete();
            }
            else if(f.isDirectory()) {
                emptyDirectory(f);
                System.out.println("Deleting folder: " + f.getName());
                f.delete();
            }
        }
    }

    public static void deleteDirectory(File folder) {
        File [] files = folder.listFiles();
        for(File f : files) {
            if(f.isFile()) {
                System.out.println("Deleting file: " + f.getName());
                f.delete();
            }
            else if(f.isDirectory()) {
                System.out.println("Entering folder: " + folder.getName());
                deleteDirectory(f);
            }
        }
        System.out.println("Deleting folder: " + folder.getName());
        folder.delete();
    }

    public static void readFromSourceAppendToDestination(File source, File destination) throws IOException {
        RandomAccessFile reader = null;
        RandomAccessFile writer = null;
        try {
            reader = new RandomAccessFile(source, "r");
            writer = new RandomAccessFile(destination, "rw");

            writer.seek(writer.length());
            int n;
            while ((n = reader.read()) != -1) {
                writer.write(n);
            }
        }
        catch (Exception e) {}
        finally {
            if (reader != null) {
                reader.close();
            }
            if (writer != null) {
                writer.close();
            }
        }
    }

    public static void recursivelyCopyFilesBiggerThan(String source, String destination, long size) throws IOException {
        File from = new File(source);
        File to = new File(destination);

        if(!from.exists()) {
            System.out.println("Input file does not exist");
            return;
        }
        if(!from.isDirectory()) {
            System.out.println("Input file is not a directory");
            return;
        }
        if(!to.exists()) {
            to.mkdirs();
        }
        if(!to.isDirectory()) {
            System.out.println("Output file is not a directory");
            return;
        }

        File [] files = from.listFiles();
        for(File file : files) {
            if(file.isDirectory()) {
                recursivelyCopyFilesBiggerThan(file.getAbsolutePath(), destination, size);
            }
            else {
                if(file.length() <= size) {
                    continue;
                }
                File destinationFile = new File(destination, file.getName());
                if(!destinationFile.exists()) {
                    destinationFile.createNewFile();
                }

                RandomAccessFile reader = null;
                RandomAccessFile writer = null;

                try {
                    reader = new RandomAccessFile(file, "r");
                    writer = new RandomAccessFile(destinationFile, "rw");

                    int n;
                    while ((n = reader.read()) != -1) {
                        writer.write(n);
                    }
                }
                catch (Exception e) {}
                finally {
                    if (reader != null) {
                        reader.close();
                    }
                    if (writer != null) {
                        writer.close();
                    }
                }
            }
        }
    }

    public static void copyFileToFolder(String sourceFilePath, String destinationFolderPath) throws IOException {
        File from = new File(sourceFilePath);
        File to = new File(destinationFolderPath, sourceFilePath);

        if(!from.exists()) {
            System.out.println("Input file does not exist");
            return;
        }
        if(!from.isFile()) {
            System.out.println("Input file is not a file");
            return;
        }

        RandomAccessFile reader = null;
        RandomAccessFile writer = null;

        try {
            reader = new RandomAccessFile(from, "r");
            writer = new RandomAccessFile(to, "rw");

            int n;
            while ((n = reader.read()) != -1) {
                writer.write(n);
            }
        }
        catch (Exception e) {}
        finally {
            if (reader != null) {
                reader.close();
            }
            if (writer != null) {
                writer.close();
            }
        }
    }

    public static void readAndWriteBackwards(File from, File to) throws IOException {
        RandomAccessFile reader = null;
        RandomAccessFile writer = null;

        try {
            reader = new RandomAccessFile(from, "r");
            writer = new RandomAccessFile(to, "rw");
            int i = 1;
            while(i <= reader.length()) {
                int position = (int)reader.length() - i;
                reader.seek(position);
                writer.write(reader.read());
                i++;
            }
        }
        catch (Exception e) {}
        finally {
            if (reader != null) {
                reader.close();
            }
            if (writer != null) {
                writer.close();
            }
        }
    }

    public static void main(String[] args) throws IOException {
        readAndWriteBackwards(new File("from.txt"), new File("to.txt"));
    }

}