org.axonframework.eventhandling

Class GapAwareTrackingToken

java.lang.Object

org.axonframework.eventhandling.GapAwareTrackingToken

All Implemented Interfaces:

Serializable, TrackingToken

public class GapAwareTrackingToken
extends Object
implements TrackingToken, Serializable

Implementation of a TrackingToken that uses the global insertion sequence number of the event to determine tracking order and additionally stores a set of possible gaps that have been detected while tracking the event store.

By storing the sequence numbers of gaps, i.e. sequence numbers of events that may have been inserted but have not been committed to the store, consumers are able to track the event store uninterruptedly even when there are gaps in the sequence numbers of events. If a gap is detected the event store can check if meanwhile this gap has been filled each time a new batch of events is fetched.

Author:

Rene de Waele

See Also:

Serialized Form

Method Summary

Modifier and Type	Method and Description
GapAwareTrackingToken	advanceTo(long index, int maxGapOffset, boolean allowGaps) Returns a new GapAwareTrackingToken instance based on this token but which has advanced to given index.
boolean	covers(TrackingToken other) Indicates whether this token covers the other token completely.
boolean	equals(Object o)
SortedSet<Long>	getGaps() Get a SortedSet of this token's gaps.
long	getIndex() Get the highest global sequence of events seen up until the point of this tracking token.
boolean	hasGaps() Check if this token contains one ore more gaps.
int	hashCode()
GapAwareTrackingToken	lowerBound(TrackingToken other) Returns a token that represents the lower bound between this and the other token.
static GapAwareTrackingToken	newInstance(long index, Collection<Long> gaps) Returns a new GapAwareTrackingToken instance based on the given index and collection of gaps.
String	toString()
TrackingToken	upperBound(TrackingToken otherToken) Returns the token that represents the furthest possible position in a stream that either this token or the given other represents.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Method Detail

newInstance

public static GapAwareTrackingToken newInstance(long index,
                                                Collection<Long> gaps)

Returns a new GapAwareTrackingToken instance based on the given index and collection of gaps.

Parameters:

index - the highest global sequence number of events up until (and including) this tracking token

gaps - global sequence numbers of events that have not been seen yet even though these sequence numbers are smaller than the current index. These missing sequence numbers may be filled in later when those events get committed to the store or may never be filled in if those events never get committed.

Returns:

a new tracking token from given index and gaps

advanceTo

public GapAwareTrackingToken advanceTo(long index,
                                       int maxGapOffset,
                                       boolean allowGaps)

Returns a new GapAwareTrackingToken instance based on this token but which has advanced to given index. Gaps that have fallen behind the index by more than the maxGapOffset will not be included in the new token.

Note that the given index should be one of the current token's gaps or be higher than the current token's index.

If allowGaps is set to false, any gaps that occur before the given index are removed from the returned token.

Parameters:

index - the global sequence number of the next event

maxGapOffset - the maximum distance between a gap and the token's index

allowGaps - whether advancing to the given index should take into account that gaps may have appeared

Returns:

the new token that has advanced from the current token

getIndex

public long getIndex()

Get the highest global sequence of events seen up until the point of this tracking token.

Returns:

the highest global event sequence number seen so far

getGaps

public SortedSet<Long> getGaps()

Get a SortedSet of this token's gaps.

Returns:

the gaps of this token

lowerBound

public GapAwareTrackingToken lowerBound(TrackingToken other)

Description copied from interface: TrackingToken

Returns a token that represents the lower bound between this and the other token. Effectively, the returned token will cause messages not received by both this and the other token to be redelivered.

Specified by:

lowerBound in interface TrackingToken

Parameters:

other - The token to compare to this one

Returns:

The token representing the lower bound of the two

upperBound

public TrackingToken upperBound(TrackingToken otherToken)

Description copied from interface: TrackingToken

Returns the token that represents the furthest possible position in a stream that either this token or the given other represents. Effectively, this means this token will only deliver messages that neither this, nor the other have been received.

Specified by:

upperBound in interface TrackingToken

Parameters:

otherToken - The token to compare this token to

Returns:

a token that represents the furthest position of this or the other stream

covers

public boolean covers(TrackingToken other)

Description copied from interface: TrackingToken

Indicates whether this token covers the other token completely. That means that this token represents a position in a stream that has received all of the messages that a stream represented by the other token has received.

Specified by:

covers in interface TrackingToken

Parameters:

other - The token to compare to this one

Returns:

true if this token covers the other, otherwise false

hasGaps

public boolean hasGaps()

Check if this token contains one ore more gaps.

Returns:

true if this token contains gaps, false otherwise

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

toString

public String toString()

Overrides:

toString in class Object