code: public static PublicKey readPublicKey(InputStream pemStream) {
  		final Certificate certificate = KeyUtil.readX509Certificate(pemStream);
  		if(null == certificate) {
  			return null;
  		}
  		return certificate.getPublicKey();
  	}
docs: 读取PEM格式的公钥
  
  @param pemStream pem流
  @return {@link PublicKey}
  @since 4.5.2