[Java] File encrypt/decrypt with AES 128

Main.java

package ru.psqq;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;
import java.security.Key;
import java.security.MessageDigest;
import java.util.Base64;

public class Main {

    private static final String ALGORITHM = "AES";
    private static final String TRANSFORMATION = "AES";

    private static final String KEY = "ZZHHYYTTUUHHGGRR";
    private static final String IV = "AAACCCDDDYYUURRS";

    public static void main(String[] args) {
        try {
            test_encrypt_decrypt();
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
            System.exit(1);
        }
    }

    public static void test_encrypt_decrypt() throws Exception {
        // encrypt "in.txt" -> "out.txt"
        String s = readFile("in.txt");
        String res = encrypt("mykey", IV, s);
        PrintWriter writer = new PrintWriter("out.txt", "UTF-8");
        writer.print(res);
        writer.close();
        // decrypt "out.txt" -> "out2.txt"
        s = readFile("out.txt");
        res = decrypt("mykey", IV, s);
        writer = new PrintWriter("out2.txt", "UTF-8");
        writer.print(res);
        writer.close();
    }

    public static String encrypt(String key, String iv, String msg) throws Exception {
        byte[] bytesOfKey = key.getBytes("UTF-8");
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] keyBytes = md.digest(bytesOfKey);

        final byte[] ivBytes = iv.getBytes();

        SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, new IvParameterSpec(ivBytes));

        final byte[] resultBytes = cipher.doFinal(msg.getBytes());
        return Base64.getMimeEncoder().encodeToString(resultBytes);
    }

    public static void test_decrypt() throws Exception {
        String s = readFile("in.txt");
        String res = decrypt(KEY, IV, s);
        System.out.println("res:\n" + res);
    }

    public static String decrypt(String key, String iv, String encrypted) throws Exception {
        byte[] bytesOfKey = key.getBytes("UTF-8");
        MessageDigest md = MessageDigest.getInstance("MD5");
        byte[] keyBytes = md.digest(bytesOfKey);

        final byte[] ivBytes = iv.getBytes();

        final byte[] encryptedBytes = Base64.getMimeDecoder().decode(encrypted);

        SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");
        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec, new IvParameterSpec(ivBytes));

        final byte[] resultBytes = cipher.doFinal(encryptedBytes);
        return new String(resultBytes);
    }

    public static String readFile(String filename) throws Exception {
        BufferedReader br = new BufferedReader(new FileReader(filename));
        try {
            StringBuilder sb = new StringBuilder();
            String line = br.readLine();
            while (line != null) {
                sb.append(line);
                sb.append(System.lineSeparator());
                line = br.readLine();
            }
            String everything = sb.toString();
            return everything;
        } finally {
            br.close();
        }
    }

    public static void test_read_file() throws Exception {
        String s = readFile("in.txt");
        System.out.println("in.txt:\n" + s);
    }

    public static void encrypt(String key, File inputFile, File outputFile) throws Exception {
        doCrypto(Cipher.ENCRYPT_MODE, key, inputFile, outputFile);
    }

    public static void decrypt(String key, File inputFile, File outputFile) throws Exception {
        doCrypto(Cipher.DECRYPT_MODE, key, inputFile, outputFile);
    }

    static void doCrypto(int cipherMode, String key, File inputFile,
                          File outputFile) throws Exception {
        Key secretKey = new SecretKeySpec(key.getBytes(), ALGORITHM);
        Cipher cipher = Cipher.getInstance(TRANSFORMATION);
        cipher.init(cipherMode, secretKey);

        FileInputStream inputStream = new FileInputStream(inputFile);
        byte[] inputBytes = new byte[(int) inputFile.length()];
        inputStream.read(inputBytes);

        byte[] outputBytes = cipher.doFinal(inputBytes);

        FileOutputStream outputStream = new FileOutputStream(outputFile);
        outputStream.write(outputBytes);

        inputStream.close();
        outputStream.close();
    }

    public static void test_doCrypto(String filename) throws Exception {
        String key = "Mary has one cat";
        File inputFile = new File("document.txt");
        File encryptedFile = new File("document.encrypted");
        File decryptedFile = new File("document.decrypted");

        encrypt(key, inputFile, encryptedFile);
        decrypt(key, encryptedFile, decryptedFile);
    }

    public static void test_write_to_file(String filename) throws Exception {
        PrintWriter writer = new PrintWriter(filename, "UTF-8");
        writer.println("The first line");
        writer.println("The second line");
        writer.close();
    }
}