Package org.axonframework.messaging.core.annotation

Interface MessageHandlingMember<T>

Type Parameters:

T - The type of entity to which the message handler will delegate the actual handling of the message

All Known Subinterfaces:

CommandHandlingMember<T>, EventHandlingMember<T>, MessageInterceptingMember<T>, QueryHandlingMember<T>

All Known Implementing Classes:

MethodInvokingMessageHandlingMember, WrappedMessageHandlingMember

@Internal
public interface MessageHandlingMember<T>

Interface describing a handler for specific messages targeting entities of a specific type.

Since:

3.0.0

Author:

Allard Buijze

Method Summary

Modifier and Type	Method	Description
default <R> Optional<R>	attribute(String attributeKey)	Retrieve a single attributes for the given attributeKey.
boolean	canHandle(Message message, ProcessingContext context)	Checks if this handler is capable of handling the given message.
boolean	canHandleMessageType(Class<? extends Message> messageType)	Checks if this handler is capable of handling Message implementations of the given messageType.
default boolean	canHandleType(Class<?> payloadType)	Checks if this handler is capable of handling messages with the given payloadType.
default Class<?>	declaringClass()	Gets the declaring class of this Message Handling Member.
MessageStream<?>	handle(Message message, ProcessingContext context, T target)	Handles the given message within the given context by invoking the appropriate method on given target.
Object	handleSync(Message message, ProcessingContext context, T target)	Deprecated, for removal: This API element is subject to removal in a future version. In favor of handle(Message, ProcessingContext, Object).
Class<?>	payloadType()	Returns the payload type of messages that can be processed by this handler.
default int	priority()	Returns a number representing the priority of this handler over other handlers capable of processing the same message.
default String	signature()	Returns the signature of the member.
<HT> Optional<HT>	unwrap(Class<HT> handlerType)	Returns the wrapped handler object if its type is an instance of the given handlerType.

Method Details

payloadType

Class<?> payloadType()

Returns the payload type of messages that can be processed by this handler.

Returns:

The payload type of messages expected by this handler

priority

default int priority()

Returns a number representing the priority of this handler over other handlers capable of processing the same message.

In general, a handler with a higher priority will receive the message before (or instead of) handlers with a lower priority. However, the priority value may not be the only indicator that is used to determine the order of invocation. For instance, a message processor may decide to ignore the priority value if one message handler is a more specific handler of the message than another handler.

Returns:

Number indicating the priority of this handler over other handlers

canHandle

boolean canHandle(@Nonnull
 Message message,
 @Nonnull
 ProcessingContext context)

Checks if this handler is capable of handling the given message.

Parameters:

message - The message that is to be handled.

context - The context in which the message is being handled.

Returns:

true if the handler is capable of handling the message, false otherwise.

canHandleType

default boolean canHandleType(@Nonnull
 Class<?> payloadType)

Checks if this handler is capable of handling messages with the given payloadType.

Parameters:

payloadType - The payloadType of a message that is to be handled

Returns:

true if the handler is capable of handling the message with given type, false otherwise.

canHandleMessageType

boolean canHandleMessageType(@Nonnull
 Class<? extends Message> messageType)

Checks if this handler is capable of handling Message implementations of the given messageType.

It is recommended to suppress the raw type use validation of the messageType parameter when implementing this method, as usage of this method with a Message generic would required reflection or casting otherwise.

Parameters:

messageType - The Message's type to check if it can be handled by this handler.

Returns:

true if this handler can handle the given messageType, false otherwise.

handleSync

@Internal
@Deprecated(forRemoval=true,
            since="5.2.0")
Object handleSync(@Nonnull
 Message message,
 @Nonnull
 ProcessingContext context,
 @Nullable
 T target)
           throws Exception

Deprecated, for removal: This API element is subject to removal in a future version.

In favor of handle(Message, ProcessingContext, Object).

Handles the given message by invoking the appropriate method on given target. This may result in an exception if the given target is not capable of handling the message or if an exception is thrown during invocation of the method.

Parameters:

message - The message to handle.

context - The context in which the message is being handled.

target - The target to handle the message.

Returns:

The message handling result in case the invocation was successful.

Throws:

Exception - when there was a problem that prevented invocation of the method or if an exception was thrown from the invoked method.

handle

MessageStream<?> handle(@Nonnull
 Message message,
 @Nonnull
 ProcessingContext context,
 @Nullable
 T target)

Handles the given message within the given context by invoking the appropriate method on given target.

This may result in an exception if the given target is not capable of handling the message or if an exception is thrown during invocation of the method. These exceptions should be caught and passed along in a failed MessageStream.

Parameters:

message - The message to handle.

context - The context in which the message is being handled.

target - The target to handle the message.

Returns:

The MessageStream containing the response(s), if any, from handling the given message.

unwrap

<HT> Optional<HT> unwrap(Class<HT> handlerType)

Returns the wrapped handler object if its type is an instance of the given handlerType. For instance, if this method is invoked with Executable and the message is handled by a method of the target entity, then this method will return the method handle as a Method.

Type Parameters:

HT - The wrapped handler type

Parameters:

handlerType - The expected type of the wrapped handler

Returns:

An Optional containing the wrapped handler object or an empty Optional if the handler is not an instance of the given handlerType

declaringClass

default Class<?> declaringClass()

Gets the declaring class of this Message Handling Member.

Returns:

the declaring class of this Message Handling Member

signature

default String signature()

Returns the signature of the member. This may be used in logging or exceptions to demarcate the actual class member invoked. If this member does not have a signature, "__unknown__" is returned.

Returns:

the signature of the handling member

attribute

default <R> Optional<R> attribute(String attributeKey)

Retrieve a single attributes for the given attributeKey. If this MessageHandlingMember does not hold a value referencing the attributeKey, an Optional.empty() is returned. Otherwise, a non-empty Optional containing the attribute will be provided.

When using the method, consider checking the HandlerAttributes for a list of common handler attributes.

Type Parameters:

R - The value type of the returned attribute.

Parameters:

attributeKey - The key to retrieve an attribute for.

Returns:

A non-empty Optional of the attribute referencing the given attributeKey. Otherwise, an Optional.empty() will be returned.