Package org.axonframework.messaging.core.annotation

Class MessageStreamResolverUtils

java.lang.Object

org.axonframework.messaging.core.annotation.MessageStreamResolverUtils

@Internal
public class MessageStreamResolverUtils
extends Object

Utility class that can resolve the result of any MessageHandler into the expected corresponding MessageStream.

Whether a returned Iterable represents several results or one result that happens to be a collection cannot be derived from the value itself. Callers therefore choose the cardinality up front: resolveToStream(Object, MessageTypeResolver) spreads an Iterable over as many Messages as it holds elements, while resolveToSingleStream(Object, MessageTypeResolver) carries it as the Message.payload() of a single Message. Both unwrap asynchronous containers such as CompletableFuture first, so that List<T> and CompletableFuture<List<T>> yield the same cardinality.

This utility class currently has a drawback, which is that it only takes the "top level" type into account. Differently put, if we receive a Mono<Message> as the given result, we will push that Message through the given typeResolver and make it the Message.payload().

This is a known limitation that will be supported in due time.

Since:

5.0.0

Author:

Simon Zambrovski, Steven van Beelen

Method Summary

Modifier and Type	Method	Description
static MessageStream<?>	resolveToSingleStream(@Nullable Object result, MessageTypeResolver typeResolver)	Resolves the given result into a MessageStream carrying at most one Message, using the typeResolver when that Message is constructed to define the MessageType.
static MessageStream<?>	resolveToStream(@Nullable Object result, MessageTypeResolver typeResolver)	Resolves the given result into a MessageStream that may carry several Messages, using the typeResolver when a Message is constructed to define the MessageType.

Methods inherited from class java.lang.Object

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

Method Details

resolveToStream

public static MessageStream<?> resolveToStream(@Nullable Object result,
 MessageTypeResolver typeResolver)

Resolves the given result into a MessageStream that may carry several Messages, using the typeResolver when a Message is constructed to define the MessageType.

Is able to switch between Optional, CompletableFuture, Iterable, Stream, Mono, and Flux. An Iterable or Stream is spread over as many Messages as it holds elements, also when wrapped in a CompletableFuture or Optional. If none of the above apply, MessageStream.just(Message) will be used. If the given result is null, MessageStream.empty() is returned.

Use resolveToSingleStream(Object, MessageTypeResolver) for handlers that produce exactly one result, as those must carry a returned collection as a whole instead of spreading it.

Parameters:

result - The result to map into a MessageStream.

typeResolver - The MessageTypeResolver used to resolve the MessageType for Messages that are held in the returned MessageStream.

result - the result to map into a MessageStream

typeResolver - the MessageTypeResolver used to resolve the MessageType for Messages that are held in the returned MessageStream

Returns:

a MessageStream based on the given result

resolveToSingleStream

public static MessageStream<?> resolveToSingleStream(@Nullable Object result,
 MessageTypeResolver typeResolver)

Resolves the given result into a MessageStream carrying at most one Message, using the typeResolver when that Message is constructed to define the MessageType.

Behaves like resolveToStream(Object, MessageTypeResolver), except that a returned Iterable becomes the Message.payload() of a single Message rather than being spread over one Message per element. This suits handlers that produce exactly one result, such as command handlers, for which spreading would mean silently discarding all but the first element.

Parameters:

result - the result to map into a MessageStream

typeResolver - the MessageTypeResolver used to resolve the MessageType for the Message that is held in the returned MessageStream

Returns:

a MessageStream based on the given result