Package org.axonframework.messaging.deadletter

Interface SequencedDeadLetterQueue<M extends Message>

Type Parameters:

M - An implementation of Message contained in the dead letters within this queue.

All Known Implementing Classes:

CachingSequencedDeadLetterQueue, InMemorySequencedDeadLetterQueue, JdbcSequencedDeadLetterQueue, JpaSequencedDeadLetterQueue

public interface SequencedDeadLetterQueue<M extends Message>

Interface describing the required functionality for a dead letter queue. Contains several FIFO-ordered sequences of dead letters.

The contained sequences are uniquely identifiable through the "sequence identifier." Dead-letters are kept in the form of a DeadLetter. It is highly recommended to use the process operation (or any of its variants) to consume letters from the queue for retrying. This method ensures sequences cannot be concurrently accessed, thus protecting the user against handling messages out of order.

All methods in this interface return CompletableFuture to support asynchronous implementations. In-memory implementations may simply return completed futures, while persistent implementations (JPA, JDBC, etc.) can leverage the async nature for non-blocking I/O.

Since:

4.6.0

Author:

Steven van Beelen, Allard Buijze, Milan Savic, Mitchell Herrijgers

See Also:

• DeadLetter

Method Summary

Modifier and Type	Method	Description
CompletableFuture<Long>	amountOfSequences(@Nullable ProcessingContext context)	Returns the number of unique sequences contained in this queue.
CompletableFuture<Void>	clear(@Nullable ProcessingContext context)	Clears out all dead letters present in this queue.
CompletableFuture<Boolean>	contains(Object sequenceIdentifier, @Nullable ProcessingContext context)	Check whether there's a sequence of dead letters for the given sequenceIdentifier.
CompletableFuture<Iterable<Iterable<DeadLetter<? extends M>>>>	deadLetters(@Nullable ProcessingContext context)	Return all dead letter sequences held by this queue.
CompletableFuture<Iterable<DeadLetter<? extends M>>>	deadLetterSequence(Object sequenceIdentifier, @Nullable ProcessingContext context)	Return all the dead letters for the given sequenceIdentifier in insert order.
CompletableFuture<Void>	enqueue(Object sequenceIdentifier, DeadLetter<? extends M> letter, @Nullable ProcessingContext context)	Enqueues a dead letter containing an implementation of M to this queue.
default CompletableFuture<Boolean>	enqueueIfPresent(Object sequenceIdentifier, Supplier<DeadLetter<? extends M>> letterBuilder, @Nullable ProcessingContext context)	Enqueue the result of the given letterBuilder only if there already are other dead letters with the same sequenceIdentifier present in this queue.
CompletableFuture<Void>	evict(DeadLetter<? extends M> letter, @Nullable ProcessingContext context)	Evict the given letter from this queue.
CompletableFuture<Boolean>	isFull(Object sequenceIdentifier, @Nullable ProcessingContext context)	Validates whether this queue is full for the given sequenceIdentifier.
default CompletableFuture<Boolean>	process(Function<DeadLetter<? extends M>,CompletableFuture<EnqueueDecision<M>>> processingTask, @Nullable ProcessingContext context)	Process a single sequence of enqueued dead letters with the given processingTask.
CompletableFuture<Boolean>	process(Predicate<DeadLetter<? extends M>> sequenceFilter, Function<DeadLetter<? extends M>,CompletableFuture<EnqueueDecision<M>>> processingTask, @Nullable ProcessingContext context)	Process a single sequence of enqueued dead letters through the given processingTask matching the sequenceFilter.
CompletableFuture<Void>	requeue(DeadLetter<? extends M> letter, UnaryOperator<DeadLetter<? extends M>> letterUpdater, @Nullable ProcessingContext context)	Reenters the given letter, updating the contents with the letterUpdater.
CompletableFuture<Long>	sequenceSize(Object sequenceIdentifier, @Nullable ProcessingContext context)	Returns the number of dead letters for the sequence matching the given sequenceIdentifier contained in this queue.
CompletableFuture<Long>	size(@Nullable ProcessingContext context)	Returns the number of dead letters contained in this queue.

Method Details

enqueue

CompletableFuture<Void> enqueue(Object sequenceIdentifier,
 DeadLetter<? extends M> letter,
 @Nullable ProcessingContext context)

Enqueues a dead letter containing an implementation of M to this queue.

The dead letter will be appended to a sequence depending on the sequenceIdentifier. If there is no sequence yet, it will construct one.

Parameters:

sequenceIdentifier - The identifier of the sequence the letter belongs to.

letter - The DeadLetter to enqueue.

context - the processing context within which to enqueue the given letter

Returns:

A CompletableFuture that completes when the operation is done. The future completes exceptionally with a DeadLetterQueueOverflowException when this queue is full.

enqueueIfPresent

default CompletableFuture<Boolean> enqueueIfPresent(Object sequenceIdentifier,
 Supplier<DeadLetter<? extends M>> letterBuilder,
 @Nullable ProcessingContext context)

Enqueue the result of the given letterBuilder only if there already are other dead letters with the same sequenceIdentifier present in this queue.

Parameters:

sequenceIdentifier - The identifier of the sequence to store the result of the letterBuilder in.

letterBuilder - The DeadLetter builder constructing the letter to enqueue. Only invoked if the given sequenceIdentifier is contained.

context - the processing context within which to enqueue the result of the given letterBuilder if there is a sequence for the given sequenceIdentifier

Returns:

A CompletableFuture with true if there are dead letters for the given sequenceIdentifier and thus the letterBuilder's outcome is inserted. Otherwise, the future completes with false. The future completes exceptionally with a DeadLetterQueueOverflowException when this queue is isFull(Object, ProcessingContext) for the given sequenceIdentifier.

evict

CompletableFuture<Void> evict(DeadLetter<? extends M> letter,
 @Nullable ProcessingContext context)

Evict the given letter from this queue. Nothing happens if the dead letter does not exist in this queue.

Parameters:

letter - The dead letter to evict from this queue.

context - the processing context within which to evict the given letter

Returns:

A CompletableFuture that completes when the eviction is done.

requeue

CompletableFuture<Void> requeue(DeadLetter<? extends M> letter,
 UnaryOperator<DeadLetter<? extends M>> letterUpdater,
 @Nullable ProcessingContext context)

Reenters the given letter, updating the contents with the letterUpdater. This method should be invoked if processing decided to keep the letter in the queue.

This operation adjusts the DeadLetter.lastTouched(). It may adjust the DeadLetter.cause() and DeadLetter.diagnostics(), depending on the given letterUpdater.

Parameters:

letter - The dead letter to reenter in this queue.

letterUpdater - A lambda taking in the given letter and updating the entry for requeueing. This may adjust the DeadLetter.cause() and DeadLetter.diagnostics(), for example.

context - the processing context within which to requeue the given letter

Returns:

A CompletableFuture that completes when the requeue is done. The future completes exceptionally with a NoSuchDeadLetterException if the given letter does not exist in the queue.

contains

CompletableFuture<Boolean> contains(Object sequenceIdentifier,
 @Nullable ProcessingContext context)

Check whether there's a sequence of dead letters for the given sequenceIdentifier.

Parameters:

sequenceIdentifier - The identifier used to validate for contained dead letters instances.

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with true if there are dead letters present for the given sequenceIdentifier, false otherwise.

deadLetterSequence

CompletableFuture<Iterable<DeadLetter<? extends M>>> deadLetterSequence(Object sequenceIdentifier,
 @Nullable ProcessingContext context)

Return all the dead letters for the given sequenceIdentifier in insert order.

Parameters:

sequenceIdentifier - The identifier of the sequence of dead letters to return.

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with all the dead letters for the given sequenceIdentifier in insert order.

deadLetters

CompletableFuture<Iterable<Iterable<DeadLetter<? extends M>>>> deadLetters(@Nullable ProcessingContext context)

Return all dead letter sequences held by this queue. The sequences are not necessarily returned in insert order.

Parameters:

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with all dead letter sequences held by this queue.

isFull

CompletableFuture<Boolean> isFull(Object sequenceIdentifier,
 @Nullable ProcessingContext context)

Validates whether this queue is full for the given sequenceIdentifier.

This method returns true either when the maximum amount of sequences or the maximum sequence size is reached.

Parameters:

sequenceIdentifier - The identifier of the sequence to validate for.

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with true either when the limit of this queue is reached. Contains false otherwise.

size

CompletableFuture<Long> size(@Nullable ProcessingContext context)

Returns the number of dead letters contained in this queue.

Parameters:

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with the number of dead letters contained in this queue.

sequenceSize

CompletableFuture<Long> sequenceSize(Object sequenceIdentifier,
 @Nullable ProcessingContext context)

Returns the number of dead letters for the sequence matching the given sequenceIdentifier contained in this queue.

Note that there's a window of opportunity where the size might exceed the maximum sequence size to account for concurrent usage.

Parameters:

sequenceIdentifier - The identifier of the sequence to retrieve the size from.

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with the number of dead letters for the sequence matching the given sequenceIdentifier.

amountOfSequences

CompletableFuture<Long> amountOfSequences(@Nullable ProcessingContext context)

Returns the number of unique sequences contained in this queue.

Note that there's a window of opportunity where the size might exceed the maximum amount of sequences to account for concurrent usage of this dead letter queue.

Parameters:

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture with the number of unique sequences contained in this queue.

process

CompletableFuture<Boolean> process(Predicate<DeadLetter<? extends M>> sequenceFilter,
 Function<DeadLetter<? extends M>,CompletableFuture<EnqueueDecision<M>>> processingTask,
 @Nullable ProcessingContext context)

Process a single sequence of enqueued dead letters through the given processingTask matching the sequenceFilter. It will pick the oldest available sequence, determined by the DeadLetter.lastTouched() field of the first entry in each sequence.

Note that only a single matching sequence is processed! Furthermore, only the first dead letter is validated, because it is the blocker for the processing of the rest of the sequence.

Uses the EnqueueDecision returned by the processingTask to decide whether to evict(DeadLetter, ProcessingContext) or requeue(DeadLetter, UnaryOperator, ProcessingContext) a dead letter from the selected sequence. The processingTask is invoked as long as letters are present in the selected sequence and the result of processing returns false for EnqueueDecision.shouldEnqueue() decision. The latter means the dead letter should be evicted.

This operation protects against concurrent invocations of the processingTask on the filtered sequence. Doing so ensures enqueued messages are handled in order.

Parameters:

sequenceFilter - A lambda selecting the sequences within this queue to process with the processingTask.

processingTask - A function processing a dead letter. Returns a CompletableFuture with an EnqueueDecision used to deduce whether to evict(DeadLetter, ProcessingContext) or requeue(DeadLetter, UnaryOperator, ProcessingContext) the dead letter.

context - the ProcessingContext in which the dead letters are processed

Returns:

A CompletableFuture with true if an entire sequence of dead letters was processed successfully, false otherwise. This means the processingTask processed all dead letters of a sequence and the outcome was to evict each instance.

process

default CompletableFuture<Boolean> process(Function<DeadLetter<? extends M>,CompletableFuture<EnqueueDecision<M>>> processingTask,
 @Nullable ProcessingContext context)

Process a single sequence of enqueued dead letters with the given processingTask. It will pick the oldest available sequence, determined by the DeadLetter.lastTouched() field of the first entry in each sequence.

Note that only a single matching sequence is processed!

Uses the EnqueueDecision returned by the processingTask to decide whether to evict(DeadLetter, ProcessingContext) or requeue(DeadLetter, UnaryOperator, ProcessingContext) the dead letter. The processingTask is invoked as long as letters are present in the selected sequence and the result of processing returns false for EnqueueDecision.shouldEnqueue() decision. The latter means the dead letter should be evicted.

This operation protects against concurrent invocations of the processingTask on the filtered sequence. Doing so ensures enqueued messages are handled in order.

Parameters:

processingTask - A function processing a dead letter. Returns a CompletableFuture with an EnqueueDecision used to deduce whether to evict(DeadLetter, ProcessingContext) or requeue(DeadLetter, UnaryOperator, ProcessingContext) the dead letter.

context - the ProcessingContext in which the dead letters are processed

Returns:

A CompletableFuture with true if an entire sequence of dead letters was processed successfully, false otherwise. This means the processingTask processed all dead letters of a sequence and the outcome was to evict each instance.

clear

CompletableFuture<Void> clear(@Nullable ProcessingContext context)

Clears out all dead letters present in this queue.

Parameters:

context - the ProcessingContext wherein this operation is invoked, if any

Returns:

A CompletableFuture that completes when all dead letters have been cleared.