private List<Component> componentFilter() {
      Type jsonType = new TypeToken<List<Component>>() {}.getType();
      return StageUtils.getGson().fromJson(getCommandParameterValue(COMPONENT_FILTER), jsonType);
    }
Convert a collection of {@link Component}s to a host filter.

@param components the collection of relevant {@link Component}s
@return a set of hostnames of hosts to include in an operation
ambari-server/src/main/java/org/apache/ambari/server/controller/DeleteIdentityHandler.java