code: public static PublicKey readPublicKeyFromCert(InputStream in) {
  		final Certificate certificate = readX509Certificate(in);
  		if (null != certificate) {
  			return certificate.getPublicKey();
  		}
  		return null;
  	}
docs: 读取X.509 Certification文件中的公钥<br>
  Certification为证书文件<br>
  see: https://www.cnblogs.com/yinliang/p/10115519.html
  
  @param in {@link InputStream} 如果想从文件读取.cer文件，使用 {@link FileUtil#getInputStream(java.io.File)} 读取
  @return {@link KeyStore}
  @since 4.5.2