private String getStringProperty(Map<String, Object> propertyMap, String propertyId) {
    String value = null;

    if (propertyMap != null) {
      Object o = propertyMap.get(propertyId);
      if (o instanceof String) {
        value = (String) o;
      }
    }

    return value;
  }
Retrieves the requested configuration resources

@param requestedIds the requested properties ids
@param propertyMap  the request properties
@return a set of resources built from the found data
@throws NoSuchResourceException if the requested resource was not found
ambari-server/src/main/java/org/apache/ambari/server/controller/internal/RootServiceComponentConfigurationResourceProvider.java