Java バックエンド テクノロジを使用してデータの暗号化と復号化を実装するにはどうすればよいですか?

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;
import java.util.Base64;

public class SymmetricEncryptionExample {
    public static String encrypt(String plainText, String key) throws Exception {
        SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        byte[] encryptedBytes = cipher.doFinal(plainText.getBytes());
        return Base64.getEncoder().encodeToString(encryptedBytes);
    }

    public static String decrypt(String encryptedText, String key) throws Exception {
        SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES/ECB/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);
        byte[] encryptedBytes = Base64.getDecoder().decode(encryptedText);
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        return new String(decryptedBytes);
    }

    public static void main(String[] args) {
        try {
            String plainText = "Hello, encryption!";
            String key = "Thisisa128bitKey";
            String encryptedText = encrypt(plainText, key);
            System.out.println("Encrypted text: " + encryptedText);
            String decryptedText = decrypt(encryptedText, key);
            System.out.println("Decrypted text: " + decryptedText);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

import javax.crypto.Cipher;
import java.security.*;

public class AsymmetricEncryptionExample {
    public static byte[] encrypt(byte[] plainText, PublicKey publicKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(plainText);
    }

    public static byte[] decrypt(byte[] encryptedText, PrivateKey privateKey) throws Exception {
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(encryptedText);
    }

    public static void main(String[] args) {
        try {
            String plainText = "Hello, encryption!";
            KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
            KeyPair keyPair = keyPairGenerator.generateKeyPair();
            PublicKey publicKey = keyPair.getPublic();
            PrivateKey privateKey = keyPair.getPrivate();
            byte[] encryptedText = encrypt(plainText.getBytes(), publicKey);
            System.out.println("Encrypted text: " + new String(encryptedText));
            byte[] decryptedText = decrypt(encryptedText, privateKey);
            System.out.println("Decrypted text: " + new String(decryptedText));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}