Package org.axonframework.messaging.core

Interface AbstractMessageStream.FetchResult<T extends @Nullable MessageStream.Entry<?>>

Type Parameters:

T - the type of value returned when available

All Known Implementing Classes:

AbstractMessageStream.FetchResult.Completed, AbstractMessageStream.FetchResult.Error, AbstractMessageStream.FetchResult.NotReady, AbstractMessageStream.FetchResult.Value

Enclosing class:

AbstractMessageStream<M extends Message>

public static sealed interface AbstractMessageStream.FetchResult<T extends @Nullable MessageStream.Entry<?>>
permits AbstractMessageStream.FetchResult.Value<T>, AbstractMessageStream.FetchResult.Error<T>, AbstractMessageStream.FetchResult.Completed<T>, AbstractMessageStream.FetchResult.NotReady<T>

Represents the result of attempting to fetch the next element from a MessageStream.

A FetchResult models four distinct outcomes:

• AbstractMessageStream.FetchResult.Value – an element is available and returned
• AbstractMessageStream.FetchResult.Completed – no element is available and no further elements will ever arrive
• AbstractMessageStream.FetchResult.NotReady – no element is available at present, but more may become available later
• AbstractMessageStream.FetchResult.Error – the stream has failed with an error

This abstraction allows implementations to distinguish between a stream that is temporarily out of elements and one that has been fully exhausted.

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static final record	AbstractMessageStream.FetchResult.Completed<T extends MessageStream.Entry<?>>	A AbstractMessageStream.FetchResult indicating that the stream is exhausted and no further elements will be produced.
static final record	AbstractMessageStream.FetchResult.Error<T extends MessageStream.Entry<?>>	A AbstractMessageStream.FetchResult representing a terminal error in the stream.
static final record	AbstractMessageStream.FetchResult.NotReady<T extends MessageStream.Entry<?>>	A AbstractMessageStream.FetchResult indicating that no element is currently available, but the stream may produce more elements in the future.
static final record	AbstractMessageStream.FetchResult.Value<T extends MessageStream.Entry<?>>	A AbstractMessageStream.FetchResult containing a successfully fetched value.

Method Summary

Static Methods

Modifier and Type	Method	Description
static <T extends MessageStream.Entry<?>> AbstractMessageStream.FetchResult<T>	completed()	Returns a FetchResult indicating that no element is available and no further elements will be produced.
static <T extends MessageStream.Entry<?>> AbstractMessageStream.FetchResult<T>	error(Throwable error)	Creates a FetchResult representing a producer side error.
static <T extends MessageStream.Entry<?>> AbstractMessageStream.FetchResult<T>	notReady()	Returns a FetchResult indicating that no element is currently available, but more elements may become available in the future.
static <T extends @Nullable MessageStream.Entry<?>> AbstractMessageStream.FetchResult<T>	of(@Nullable T value)	Creates a FetchResult representing a successfully fetched value.
static <M extends Message> AbstractMessageStream.FetchResult<MessageStream.Entry<M>>	of(MessageStream<M> delegate)	Creates a FetchResult reflecting the current observable state of the given MessageStream.

Method Details

of

static <M extends Message>
AbstractMessageStream.FetchResult<MessageStream.Entry<M>> of(MessageStream<M> delegate)

Creates a FetchResult reflecting the current observable state of the given MessageStream.

This method inspects the provided delegate in a non-blocking manner and translates its state into a corresponding FetchResult:

• If MessageStream.hasNextAvailable() returns true, this method retrieves the next entry via MessageStream.next() and returns a AbstractMessageStream.FetchResult.Value.
• If no entry is currently available and the stream is not completed, a AbstractMessageStream.FetchResult.NotReady is returned.
• If the stream is completed normally (i.e., MessageStream.error() is empty), a AbstractMessageStream.FetchResult.Completed is returned.
• If the stream is completed exceptionally, a AbstractMessageStream.FetchResult.Error is returned containing the reported error.

This method effectively adapts a MessageStream to the FetchResult-based consumption model used by AbstractMessageStream.

Note that this method may consume an entry from the delegate when one is available, as it invokes MessageStream.next(). As such, it should only be used in contexts where advancing the delegate stream is intended.

Type Parameters:

M - the message type contained in the stream

Parameters:

delegate - the MessageStream to inspect, must not be null

Returns:

a FetchResult representing the delegate's current state

Throws:

NullPointerException - if delegate is null

of

static <T extends @Nullable MessageStream.Entry<?>>
AbstractMessageStream.FetchResult<T> of(@Nullable T value)

Creates a FetchResult representing a successfully fetched value.

Type Parameters:

T - the entry type

Parameters:

value - the non-null value

Returns:

a AbstractMessageStream.FetchResult.Value containing the given value, never null

error

static <T extends MessageStream.Entry<?>>
AbstractMessageStream.FetchResult<T> error(Throwable error)

Creates a FetchResult representing a producer side error.

Type Parameters:

T - the entry type

Parameters:

error - the non-null error

Returns:

an AbstractMessageStream.FetchResult.Error representing the failure, never null

completed

static <T extends MessageStream.Entry<?>>
AbstractMessageStream.FetchResult<T> completed()

Returns a FetchResult indicating that no element is available and no further elements will be produced.

Type Parameters:

T - the entry type

Returns:

a AbstractMessageStream.FetchResult.Completed result

notReady

static <T extends MessageStream.Entry<?>>
AbstractMessageStream.FetchResult<T> notReady()

Returns a FetchResult indicating that no element is currently available, but more elements may become available in the future.

Type Parameters:

T - the entry type

Returns:

a AbstractMessageStream.FetchResult.NotReady result