encryption & decryption of a specific folder and subfolder.java

import javax.crypto.*;
import javax.crypto.spec.SecretKeySpec;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import java.util.List;
import java.util.stream.Collectors;

import static javax.crypto.Cipher.DECRYPT_MODE;
import static javax.crypto.Cipher.ENCRYPT_MODE;

public class Main {
    private static String ALGORITHM = "AES";
    private static SecretKey secretKey;
    private static Cipher encrypter;
    private static KeyGenerator keyGenerator;


    private static SecretKey generateKey() throws NoSuchAlgorithmException {
        return KeyGenerator.getInstance(ALGORITHM).generateKey();
    }

    private static String encodeKey(SecretKey key){
        return Base64.getEncoder().encodeToString(key.getEncoded());
    }

    private static byte[] decodeKey(String encodeKey){
        return Base64.getDecoder().decode(encodeKey);
    }

    private static SecretKey reconstructKey(byte[] decodedKey){
        SecretKey originalKey = new SecretKeySpec(decodedKey, 0, decodedKey.length, ALGORITHM);
        return originalKey;
    }

    public static String encrypt(Path mainFolder) throws NoSuchAlgorithmException, InvalidKeyException, IOException, BadPaddingException, IllegalBlockSizeException{
        SecretKey generatedKey = generateKey();
        String encodedKey = encodeKey(generatedKey);

        System.out.println("ENCODED KEY: " + encodedKey);

        keyGenerator = KeyGenerator.getInstance(ALGORITHM);
        try {
            encrypter = Cipher.getInstance(ALGORITHM);
        } catch (NoSuchPaddingException e) {
            e.printStackTrace();
        }

        encrypter.init(ENCRYPT_MODE, generatedKey);

        List<File> filesInFolder = Files.walk(mainFolder)
                .filter(Files::isRegularFile)
                .map(Path::toFile)
                .collect(Collectors.toList());

        for (int i = 0; i<filesInFolder.size(); i++){
            FileInputStream inputStream = new FileInputStream(filesInFolder.get(i));
            byte[] inputBytes = new byte[(int) filesInFolder.get(i).length()];
            inputStream.read(inputBytes);


            byte[] outputBytes = encrypter.doFinal(inputBytes);
            FileOutputStream outputStream = new FileOutputStream(filesInFolder.get(i));
            outputStream.write(outputBytes);
        }
        return encodedKey;
    }

    public static void decrypt(Path mainFolder, String key) throws NoSuchAlgorithmException, InvalidKeyException, IOException, BadPaddingException, IllegalBlockSizeException{
        byte[] decodedKey = decodeKey(key);
        SecretKey reconstructKey = reconstructKey(decodedKey);

        keyGenerator = KeyGenerator.getInstance(ALGORITHM);
        try {
            encrypter = Cipher.getInstance(ALGORITHM);
        } catch (NoSuchPaddingException e) {
            e.printStackTrace();
        }
        ;
        encrypter.init(DECRYPT_MODE, reconstructKey);

        List<File> filesInFolder = Files.walk(mainFolder)
                .filter(Files::isRegularFile)
                .map(Path::toFile)
                .collect(Collectors.toList());

        for (int i = 0; i<filesInFolder.size(); i++){
            FileInputStream inputStream = new FileInputStream(filesInFolder.get(i));
            byte[] inputBytes = new byte[(int) filesInFolder.get(i).length()];
            inputStream.read(inputBytes);


            byte[] outputBytes = encrypter.doFinal(inputBytes);
            FileOutputStream outputStream = new FileOutputStream(filesInFolder.get(i));
            outputStream.write(outputBytes);
        }
    }

    public static void main(String args[]){

        try {
            decrypt(Paths.get(System.getProperty("user.home") + "\\Documents\\test"), "iU87ZezdF0IZla+beBNpzg==");
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (InvalidKeyException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (BadPaddingException e) {
            e.printStackTrace();
        } catch (IllegalBlockSizeException e) {
            e.printStackTrace();
        }

    }



}