org.apache.flink.streaming.api.windowing.triggers

Class Trigger<T,W extends Window>

java.lang.Object

org.apache.flink.streaming.api.windowing.triggers.Trigger<T,W>

Type Parameters:

T - The type of elements on which this Trigger works.

W - The type of Windows on which this Trigger can operate.

All Implemented Interfaces:

Serializable

Direct Known Subclasses:

ContinuousEventTimeTrigger, ContinuousProcessingTimeTrigger, CountTrigger, DeltaTrigger, EventTimeTrigger, ProcessingTimeTrigger, PurgingTrigger

@PublicEvolving
public abstract class Trigger<T,W extends Window>
extends Object
implements Serializable

A Trigger determines when a pane of a window should be evaluated to emit the results for that part of the window.

A pane is the bucket of elements that have the same key (assigned by the KeySelector) and same Window. An element can be in multiple panes of it was assigned to multiple windows by the WindowAssigner. These panes all have their own instance of the Trigger.

Triggers must not maintain state internally since they can be re-created or reused for different keys. All necessary state should be persisted using the state abstraction available on the Trigger.TriggerContext.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Trigger.TriggerContext A context object that is given to Trigger methods to allow them to register timer callbacks and deal with state.

Constructor Summary

Constructors

Constructor and Description
Trigger()

Method Summary

Modifier and Type	Method and Description
void	clear(W window, Trigger.TriggerContext ctx) Clears any state that the trigger might still hold for the given window.
abstract TriggerResult	onElement(T element, long timestamp, W window, Trigger.TriggerContext ctx) Called for every element that gets added to a pane.
abstract TriggerResult	onEventTime(long time, W window, Trigger.TriggerContext ctx) Called when an event-time timer that was set using the trigger context fires.
abstract TriggerResult	onProcessingTime(long time, W window, Trigger.TriggerContext ctx) Called when a processing-time timer that was set using the trigger context fires.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Trigger

public Trigger()

Method Detail

onElement

public abstract TriggerResult onElement(T element,
                                        long timestamp,
                                        W window,
                                        Trigger.TriggerContext ctx)
                                 throws Exception

Called for every element that gets added to a pane. The result of this will determine whether the pane is evaluated to emit results.

Parameters:

element - The element that arrived.

timestamp - The timestamp of the element that arrived.

window - The window to which this pane belongs.

ctx - A context object that can be used to register timer callbacks.

Throws:

Exception

onProcessingTime

public abstract TriggerResult onProcessingTime(long time,
                                               W window,
                                               Trigger.TriggerContext ctx)
                                        throws Exception

Called when a processing-time timer that was set using the trigger context fires.

Parameters:

time - The timestamp at which the timer fired.

ctx - A context object that can be used to register timer callbacks.

Throws:

Exception

onEventTime

public abstract TriggerResult onEventTime(long time,
                                          W window,
                                          Trigger.TriggerContext ctx)
                                   throws Exception

Called when an event-time timer that was set using the trigger context fires.

Parameters:

time - The timestamp at which the timer fired.

ctx - A context object that can be used to register timer callbacks.

Throws:

Exception

clear

public void clear(W window,
                  Trigger.TriggerContext ctx)
           throws Exception

Clears any state that the trigger might still hold for the given window. This is called when a window is purged. Timers set using Trigger.TriggerContext.registerEventTimeTimer(long) and Trigger.TriggerContext.registerProcessingTimeTimer(long) should be deleted here as well as state acquired using Trigger.TriggerContext.getPartitionedState(StateDescriptor).

By default, this method does nothing.

Throws:

Exception