protected String getValue(String propertyName, Map<String, String> configurationMap, String defaultValue) {
    if ((configurationMap != null) && configurationMap.containsKey(propertyName)) {
      return configurationMap.get(propertyName);
    } else {
      LOGGER.debug("Ambari server configuration property [{}] hasn't been set; using default value", propertyName);
      return defaultValue;
    }
  }
Gets the configuration value for given {@link AmbariServerConfigurationKey}.
<p>
If no value is found in the supplied configuration map, the default value will be returned.

@param propertyName     the property name for which to retrieve a value
@param configurationMap a map of configuration property names to values
@param defaultValue     the default value to use in the event the propery was not set in the configuration map
@return the requested configuration value
ambari-server/src/main/java/org/apache/ambari/server/configuration/AmbariServerConfiguration.java