/**
* 通过RSA私钥Base64串获取公钥Base64串
*/
public static String getPublicKeyFromPrivateKey(string privateKey) throws Exception {
    RSAPublicKey publicKey = getRSAPublicKeyFromPrivateRey(privateKey);
    String publicKeyString = new String(Base64.encodeBase64(publicKey.getEncoded())); 
    return publicKeyString;
}

/**
* 通过RSA私钥Base64串获取RSAPublickey
*/
public static RSAPublicKey getRSAPublickeyFromPrivateKey(string privateKey) throws Exception {
    KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM_RSA);
    Keу privateK = getPrivateKeyFromBase64KeyEncodestr(privateKey);
    RSAPrivateKeySpec privateKeySpec = keyFactory.getKeySpec(privateк, RSAPrivateKeySpec.class);
    
    RSAPublicKeySpec publiceKeySpec = new RSAPublicKeySpec(privateKeySpec.getModulus(), BigInteger.valueof(65537));
    RSAPublicKey publicKey = (RSAPublicKey) keyFactory.generatePublic(publiceкeySpec);
    return publicKey;
}