public class RSAUtils {
 
    /**
     * @param plaintext 要加密的字符串
     * @param publicKeyStr 傳入的公鑰,是一個(gè)字符串
     * @return 加密后的字符串, 以Base64編碼的形式返回
     * @throws Exception 異常
     * 這個(gè)方法接受一個(gè)要加密的字符串和一個(gè)公鑰字符串,使用公鑰進(jìn)行加密,然后返回加密后的字符串
     */
    public static String encrypt(String plaintext, String publicKeyStr) throws Exception {
        PublicKey publicKey = getPublicKeyFromString(publicKeyStr);
 
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
 
        byte[] encryptedBytes = cipher.doFinal(plaintext.getBytes());
        return Base64.getEncoder().encodeToString(encryptedBytes);
    }
 
 
    /**
     * @param encryptedText 要解密的字符串
     * @param privateKeyStr 傳入的私鑰,是一個(gè)字符串
     * @return 解密后的原始字符串
     * @throws Exception 異常
     * 這個(gè)方法接受一個(gè)要解密的字符串和一個(gè)私鑰字符串,使用私鑰進(jìn)行解密,然后返回解密后的原始字符串
     */
    public static String decrypt(String encryptedText, String privateKeyStr) throws Exception {
        PrivateKey privateKey = getPrivateKeyFromString(privateKeyStr);
 
        Cipher cipher = Cipher.getInstance("RSA");
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
 
        byte[] encryptedBytes = Base64.getDecoder().decode(encryptedText);
        byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
        return new String(decryptedBytes);
    }
 
    /**
     * @return
     * @throws Exception
     * 隨機(jī)生成一個(gè)長(zhǎng)度為2048的RSA公私鑰對(duì)
     */
    public static KeyPair generateKeyPair() throws Exception {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA");
        keyPairGenerator.initialize(2048);
        return keyPairGenerator.generateKeyPair();
    }
 
    /**
     * @param publicKey
     * @return
     * 拿出剛生成Base64格式的私鑰對(duì)的公鑰字符串
     */
    public static String publicKeyToString(PublicKey publicKey) {
        return Base64.getEncoder().encodeToString(publicKey.getEncoded());
    }
 
    /**
     * @param privateKey
     * @return
     * 拿出剛生成Base64格式的私鑰對(duì)的私鑰字符串
     */
    public static String privateKeyToString(PrivateKey privateKey) {
        return Base64.getEncoder().encodeToString(privateKey.getEncoded());
    }
 
    /**
     * @param publicKeyStr
     * @return 公鑰私鑰對(duì)象
     * @throws Exception
     * 將剛拿出的Base64格式的私鑰對(duì)的私鑰字符串生成公鑰對(duì)象
     */
    public static PublicKey getPublicKeyFromString(String publicKeyStr) throws Exception {
        byte[] publicKeyBytes = Base64.getDecoder().decode(publicKeyStr);
        X509EncodedKeySpec spec = new X509EncodedKeySpec(publicKeyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        return keyFactory.generatePublic(spec);
    }
 
    /**
     * @param privateKeyStr
     * @return
     * @throws Exception
     * 將剛拿出的Base64格式的私鑰對(duì)的私鑰字符串生成私鑰對(duì)象
     */
    public static PrivateKey getPrivateKeyFromString(String privateKeyStr) throws Exception {
        byte[] privateKeyBytes = Base64.getDecoder().decode(privateKeyStr);
        PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(privateKeyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
        return keyFactory.generatePrivate(spec);
    }
 
    public static void main(String[] args) throws Exception {
        // 生成RSA密鑰對(duì)
        KeyPair keyPair = generateKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();
 
        // 將公鑰和私鑰轉(zhuǎn)換為字符串
        String publicKeyStr = publicKeyToString(publicKey);
        String privateKeyStr = privateKeyToString(privateKey);
 
        System.out.println("公鑰: " + publicKeyStr);
        System.out.println("私鑰: " + privateKeyStr);
 
        // 加密和解密測(cè)試
        String plaintext = "大白貓真厲害";
        String encryptedText = encrypt(plaintext, publicKeyStr);
        System.out.println("加密后的子串: " + encryptedText);
 
        String decryptedText = decrypt(encryptedText, privateKeyStr);
        System.out.println("解密后的子串: " + decryptedText);
    }
}