IStatefulComponent (Heron Api Documentation)

All Superinterfaces:

IComponent, Serializable

All Known Subinterfaces:

IStatefulWindowedBolt<K,V>, ITwoPhaseStatefulComponent<K,V>

All Known Implementing Classes:

BaseStatefulWindowedBolt, ComplexSink, ComplexSource, StatefulWindowedBoltExecutor, StreamletSource, SupplierSource, TransformOperator, WindowedBoltExecutor
```
public interface IStatefulComponent<K extends Serializable,V extends Serializable>
extends IComponent
```
Defines a component that saves its internal state in the State interface

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`initState(State<K,V> state)`	Initializes the state of the function or operator to that of a previous checkpoint.
`void`	`preSave(String checkpointId)`	This is a hook for the component to perform some actions just before the framework saves its state.

Methods inherited from interface org.apache.heron.api.topology.IComponent
declareOutputFields, getComponentConfiguration

- Method Detail
  - initState
```
void initState(State<K,V> state)
```
    Initializes the state of the function or operator to that of a previous checkpoint. This method is invoked when a component is executed as part of a recovery run. In case there was prior state associated with the component, the state will be empty. Stateful Spouts/Bolts are expected to hold on to the state variable to save their internal state
    Note that initialState() is called before open() or prepare().
    
    Parameters:
    
    state - the previously saved state of the component.
  - preSave
```
void preSave(String checkpointId)
```
    This is a hook for the component to perform some actions just before the framework saves its state.
    
    Parameters:
    
    checkpointId - the ID of the checkpoint