public String getAttributeValue(String configType, String propertyName, String attributeName) {
    String value = null;
    if (attributes.containsKey(configType) &&
        attributes.get(configType).containsKey(attributeName) &&
        attributes.get(configType).get(attributeName).containsKey(propertyName)) {

      value = attributes.get(configType).get(attributeName).get(propertyName);
    } else if (parentConfiguration != null) {
      value = parentConfiguration.getAttributeValue(configType, propertyName, attributeName);
    }

    return value;
  }
Get the requested attribute value from the full merged set of attributes.

@param configType     configuration type
@param propertyName   attribute property name
@param attributeName  attribute name

@return requested attribute value or null if the attribute isn't set in configuration hierarchy
ambari-server/src/main/java/org/apache/ambari/server/topology/Configuration.java