public static String getQueryStringParameterValue(HttpServletRequest request, String parameterName) {
    MultiValueMap<String, String> valueMap = getQueryStringParameters(request);
    return ((valueMap == null) || !valueMap.containsKey(parameterName))
        ? null
        : valueMap.getFirst(parameterName);
  }
Returns the value parsed from the request's query string for the given parameter name.
<p>
If more than one value for the given parameter name is found, the first value will be retured.

@param request the {@link HttpServletRequest}
@return the value for the specified query parameter; or <code>null</code> if the
requested parameter is not present
@see #getQueryStringParameters(HttpServletRequest)
ambari-server/src/main/java/org/apache/ambari/server/utils/RequestUtils.java