Package org.apache.spark.streaming

Class State<S>

Object

org.apache.spark.streaming.State<S>

Type Parameters:

S - Class of the state

public abstract class State<S>
extends Object

:: Experimental :: Abstract class for getting and updating the state in mapping function used in the mapWithState operation of a pair DStream (Scala) or a JavaPairDStream (Java).

Scala example of using State:

    // A mapping function that maintains an integer state and returns a String
    def mappingFunction(key: String, value: Option[Int], state: State[Int]): Option[String] = {
      // Check if state exists
      if (state.exists) {
        val existingState = state.get  // Get the existing state
        val shouldRemove = ...         // Decide whether to remove the state
        if (shouldRemove) {
          state.remove()     // Remove the state
        } else {
          val newState = ...
          state.update(newState)    // Set the new state
        }
      } else {
        val initialState = ...
        state.update(initialState)  // Set the initial state
      }
      ... // return something
    }

 

Java example of using State:

    // A mapping function that maintains an integer state and returns a String
    Function3<String, Optional<Integer>, State<Integer>, String> mappingFunction =
       new Function3<String, Optional<Integer>, State<Integer>, String>() {

         @Override
         public String call(String key, Optional<Integer> value, State<Integer> state) {
           if (state.exists()) {
             int existingState = state.get(); // Get the existing state
             boolean shouldRemove = ...; // Decide whether to remove the state
             if (shouldRemove) {
               state.remove(); // Remove the state
             } else {
               int newState = ...;
               state.update(newState); // Set the new state
             }
           } else {
             int initialState = ...; // Set the initial state
             state.update(initialState);
           }
           // return something
         }
       };
 

Constructor Summary

Constructors

Constructor	Description
State()

Method Summary

Modifier and Type	Method	Description
abstract boolean	exists()	Whether the state already exists
abstract S	get()	Get the state if it exists, otherwise it will throw java.util.NoSuchElementException.
final scala.Option<S>	getOption()	Get the state as a scala.Option.
abstract boolean	isTimingOut()	Whether the state is timing out and going to be removed by the system after the current batch.
abstract void	remove()	Remove the state if it exists.
final String	toString()
abstract void	update(S newState)	Update the state with a new value.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Details

State

public State()

Method Details

exists

public abstract boolean exists()

Whether the state already exists

get

public abstract S get()

Get the state if it exists, otherwise it will throw java.util.NoSuchElementException. Check with exists() whether the state exists or not before calling get().

Returns:

(undocumented)

Throws:

NoSuchElementException - If the state does not exist.

getOption

public final scala.Option<S> getOption()

Get the state as a scala.Option. It will be Some(state) if it exists, otherwise None.

Returns:

(undocumented)

isTimingOut

public abstract boolean isTimingOut()

Whether the state is timing out and going to be removed by the system after the current batch. This timeout can occur if timeout duration has been specified in the StatSpec and the key has not received any new data for that timeout duration.

Returns:

(undocumented)

remove

public abstract void remove()

Remove the state if it exists.

State cannot be updated if it has been already removed (that is, remove() has already been called) or it is going to be removed due to timeout (that is, isTimingOut() is true).

toString

public final String toString()

Overrides:

toString in class Object

update

public abstract void update(S newState)

Update the state with a new value.

State cannot be updated if it has been already removed (that is, remove() has already been called) or it is going to be removed due to timeout (that is, isTimingOut() is true).

Parameters:

newState - (undocumented)

Throws:

IllegalArgumentException - If the state has already been removed, or is going to be removed