code: public String getComponentId(int taskId) {
          if (taskId == Constants.SYSTEM_TASK_ID) {
              return Constants.SYSTEM_COMPONENT_ID;
          } else {
              return _taskToComponent.get(taskId);
          }
      }
docs: Gets the component id for the specified task id.
  The component id maps to a component id specified for a Spout or Bolt in the topology definition.
  
  @param taskId the task id
  @return the component id for the input task id