org.springframework.amqp.rabbit.listener.adapter

Class MessageListenerAdapter

java.lang.Object

org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter

All Implemented Interfaces:

MessageListener, ChannelAwareMessageListener

public class MessageListenerAdapter
extends Object
implements MessageListener, ChannelAwareMessageListener

Message listener adapter that delegates the handling of messages to target listener methods via reflection, with flexible message type conversion. Allows listener methods to operate on message content types, completely independent from the Rabbit API.

By default, the content of incoming Rabbit messages gets extracted before being passed into the target listener method, to let the target method operate on message content types such as String or byte array instead of the raw Message. Message type conversion is delegated to a Spring AMQ MessageConverter. By default, a SimpleMessageConverter will be used. (If you do not want such automatic message conversion taking place, then be sure to set the MessageConverter to null.)

If a target listener method returns a non-null object (typically of a message content type such as String or byte array), it will get wrapped in a Rabbit Message and sent to the exchange of the incoming message with the routingKey that comes from the Rabbit ReplyTo property or via specified routingKey).

Note: The sending of response messages is only available when using the ChannelAwareMessageListener entry point (typically through a Spring message listener container). Usage as MessageListener does not support the generation of response messages.

Find below some examples of method signatures compliant with this adapter class. This first example handles all Message types and gets passed the contents of each Message type as an argument. No Message will be sent back as all of these methods return void.

 public interface MessageContentsDelegate {
        void handleMessage(String text);

        void handleMessage(Map map);

        void handleMessage(byte[] bytes);

        void handleMessage(Serializable obj);
 }
 

This next example handle a Message type and gets passed the actual (raw) Message as an argument. Again, no Message will be sent back as all of these methods return void.

 public interface RawMessageDelegate {
        void handleMessage(Message message);
 }
 

This next example illustrates a Message delegate that just consumes the String contents of Messages. Notice also how the name of the Message handling method is different from the original (this will have to be configured in the attandant bean definition). Again, no Message will be sent back as the method returns void.

 public interface TextMessageContentDelegate {
        void onMessage(String text);
 }
 

This final example illustrates a Message delegate that just consumes the String contents of Messages. Notice how the return type of this method is String: This will result in the configured MessageListenerAdapter sending a Message in response.

 public interface ResponsiveTextMessageContentDelegate {
        String handleMessage(String text);
 }
 

For further examples and discussion please do refer to the Spring reference documentation which describes this class (and its attendant XML configuration) in detail.

Author:

Juergen Hoeller, Mark Pollack, Mark Fisher, Dave Syer, Gary Russell, Greg Turnquist

See Also:

setDelegate(java.lang.Object), setDefaultListenerMethod(java.lang.String), setResponseRoutingKey(String), setMessageConverter(org.springframework.amqp.support.converter.MessageConverter), SimpleMessageConverter, ChannelAwareMessageListener, AbstractMessageListenerContainer.setMessageListener(java.lang.Object)

Field Summary

Fields

Modifier and Type	Field and Description
protected org.apache.commons.logging.Log	logger Logger available to subclasses
static String	ORIGINAL_DEFAULT_LISTENER_METHOD Out-of-the-box value for the default listener method: "handleMessage".

Constructor Summary

Constructors

Constructor and Description
MessageListenerAdapter() Create a new MessageListenerAdapter with default settings.
MessageListenerAdapter(Object delegate) Create a new MessageListenerAdapter for the given delegate.
MessageListenerAdapter(Object delegate, MessageConverter messageConverter) Create a new MessageListenerAdapter for the given delegate.
MessageListenerAdapter(Object delegate, String defaultListenerMethod) Create a new MessageListenerAdapter for the given delegate while also declaring its POJO method.

Method Summary

Methods

Modifier and Type	Method and Description
protected Object[]	buildListenerArguments(Object extractedMessage) Build an array of arguments to be passed into the target listener method.
protected Message	buildMessage(com.rabbitmq.client.Channel session, Object result) Build a Rabbit message to be sent as response based on the given result object.
protected Object	extractMessage(Message message) Extract the message body from the given Rabbit message.
protected String	getDefaultListenerMethod() Return the name of the default listener method to delegate to.
protected Object	getDelegate() Return the target object to delegate message listening to.
protected String	getListenerMethodName(Message originalMessage, Object extractedMessage) Determine the name of the listener method that is supposed to handle the given message.
protected MessageConverter	getMessageConverter() Return the converter that will convert incoming Rabbit messages to listener method arguments, and objects returned from listener methods back to Rabbit messages.
protected String	getReceivedExchange(Message request)
protected Address	getReplyToAddress(Message request) Determine a reply-to Address for the given message.
protected void	handleListenerException(Throwable ex) Handle the given exception that arose during listener execution.
protected void	handleResult(Object result, Message request, com.rabbitmq.client.Channel channel) Handle the given result object returned from the listener method, sending a response message back.
protected void	initDefaultStrategies() Initialize the default implementations for the adapter's strategies.
protected Object	invokeListenerMethod(String methodName, Object[] arguments) Invoke the specified listener method.
void	onMessage(Message message) Rabbit MessageListener entry point.
void	onMessage(Message message, com.rabbitmq.client.Channel channel) Spring ChannelAwareMessageListener entry point.
protected void	postProcessChannel(com.rabbitmq.client.Channel channel, Message response) Post-process the given message producer before using it to send the response.
protected void	postProcessResponse(Message request, Message response) Post-process the given response message before it will be sent.
protected void	sendResponse(com.rabbitmq.client.Channel channel, Address replyTo, Message message) Send the given response message to the given destination.
void	setDefaultListenerMethod(String defaultListenerMethod) Specify the name of the default listener method to delegate to, for the case where no specific listener method has been determined.
void	setDelegate(Object delegate) Set a target object to delegate message listening to.
void	setEncoding(String encoding) The encoding to use when inter-converting between byte arrays and Strings in message properties.
void	setImmediatePublish(boolean immediatePublish)
void	setMandatoryPublish(boolean mandatoryPublish)
void	setMessageConverter(MessageConverter messageConverter) Set the converter that will convert incoming Rabbit messages to listener method arguments, and objects returned from listener methods back to Rabbit messages.
void	setResponseExchange(String responseExchange) Set the exchange to use when sending response messages.
void	setResponseRoutingKey(String responseRoutingKey) Set the routing key to use when sending response messages.

Methods inherited from class java.lang.Object

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

Field Detail

ORIGINAL_DEFAULT_LISTENER_METHOD

public static final String ORIGINAL_DEFAULT_LISTENER_METHOD

Out-of-the-box value for the default listener method: "handleMessage".

See Also:

Constant Field Values

logger

protected final org.apache.commons.logging.Log logger

Logger available to subclasses

Constructor Detail

MessageListenerAdapter

public MessageListenerAdapter()

Create a new MessageListenerAdapter with default settings.

MessageListenerAdapter

public MessageListenerAdapter(Object delegate)

Create a new MessageListenerAdapter for the given delegate.

Parameters:

delegate - the delegate object

MessageListenerAdapter

public MessageListenerAdapter(Object delegate,
                      MessageConverter messageConverter)

Create a new MessageListenerAdapter for the given delegate.

Parameters:

delegate - the delegate object

messageConverter - the message converter to use

MessageListenerAdapter

public MessageListenerAdapter(Object delegate,
                      String defaultListenerMethod)

Create a new MessageListenerAdapter for the given delegate while also declaring its POJO method.

Parameters:

delegate - the delegate object

defaultListenerMethod - name of the POJO method to call upon message receipt

Method Detail

setDelegate

public void setDelegate(Object delegate)

Set a target object to delegate message listening to. Specified listener methods have to be present on this target object.

If no explicit delegate object has been specified, listener methods are expected to present on this adapter instance, that is, on a custom subclass of this adapter, defining listener methods.

getDelegate

protected Object getDelegate()

Return the target object to delegate message listening to.

setEncoding

public void setEncoding(String encoding)

The encoding to use when inter-converting between byte arrays and Strings in message properties.

Parameters:

encoding - the encoding to set

setDefaultListenerMethod

public void setDefaultListenerMethod(String defaultListenerMethod)

Specify the name of the default listener method to delegate to, for the case where no specific listener method has been determined. Out-of-the-box value is "handleMessage".

See Also:

getListenerMethodName(org.springframework.amqp.core.Message, java.lang.Object)

getDefaultListenerMethod

protected String getDefaultListenerMethod()

Return the name of the default listener method to delegate to.

setResponseRoutingKey

public void setResponseRoutingKey(String responseRoutingKey)

Set the routing key to use when sending response messages. This will be applied in case of a request message that does not carry a "ReplyTo" property

Response destinations are only relevant for listener methods that return result objects, which will be wrapped in a response message and sent to a response destination.

setResponseExchange

public void setResponseExchange(String responseExchange)

Set the exchange to use when sending response messages. This is only used if the exchange from the received message is null.

Response destinations are only relevant for listener methods that return result objects, which will be wrapped in a response message and sent to a response destination.

Parameters:

responseExchange -

setMessageConverter

public void setMessageConverter(MessageConverter messageConverter)

Set the converter that will convert incoming Rabbit messages to listener method arguments, and objects returned from listener methods back to Rabbit messages.

The default converter is a SimpleMessageConverter, which is able to handle "text" content-types.

getMessageConverter

protected MessageConverter getMessageConverter()

Return the converter that will convert incoming Rabbit messages to listener method arguments, and objects returned from listener methods back to Rabbit messages.

setMandatoryPublish

public void setMandatoryPublish(boolean mandatoryPublish)

setImmediatePublish

public void setImmediatePublish(boolean immediatePublish)

onMessage

public void onMessage(Message message)

Rabbit MessageListener entry point.

Delegates the message to the target listener method, with appropriate conversion of the message argument. In case of an exception, the handleListenerException(Throwable) method will be invoked.

Note: Does not support sending response messages based on result objects returned from listener methods. Use the ChannelAwareMessageListener entry point (typically through a Spring message listener container) for handling result objects as well.

Specified by:

onMessage in interface MessageListener

Parameters:

message - the incoming Rabbit message

See Also:

handleListenerException(java.lang.Throwable), onMessage(Message, Channel)

onMessage

public void onMessage(Message message,
             com.rabbitmq.client.Channel channel)
               throws Exception

Spring ChannelAwareMessageListener entry point.

Delegates the message to the target listener method, with appropriate conversion of the message argument. If the target method returns a non-null object, wrap in a Rabbit message and send it back.

Specified by:

onMessage in interface ChannelAwareMessageListener

Parameters:

message - the incoming Rabbit message

channel - the Rabbit channel to operate on

Throws:

Exception - if thrown by Rabbit API methods

initDefaultStrategies

protected void initDefaultStrategies()

Initialize the default implementations for the adapter's strategies.

See Also:

setMessageConverter(org.springframework.amqp.support.converter.MessageConverter), SimpleMessageConverter

handleListenerException

protected void handleListenerException(Throwable ex)

Handle the given exception that arose during listener execution. The default implementation logs the exception at error level.

This method only applies when using a Rabbit MessageListener. With ChannelAwareMessageListener, exceptions get handled by the caller instead.

Parameters:

ex - the exception to handle

See Also:

onMessage(Message)

extractMessage

protected Object extractMessage(Message message)
                         throws Exception

Extract the message body from the given Rabbit message.

Parameters:

message - the Rabbit Message

Returns:

the content of the message, to be passed into the listener method as argument

Throws:

Exception - if thrown by Rabbit API methods

getListenerMethodName

protected String getListenerMethodName(Message originalMessage,
                           Object extractedMessage)
                                throws Exception

Determine the name of the listener method that is supposed to handle the given message.

The default implementation simply returns the configured default listener method, if any.

Parameters:

originalMessage - the Rabbit request message

extractedMessage - the converted Rabbit request message, to be passed into the listener method as argument

Returns:

the name of the listener method (never null)

Throws:

Exception - if thrown by Rabbit API methods

See Also:

setDefaultListenerMethod(java.lang.String)

buildListenerArguments

protected Object[] buildListenerArguments(Object extractedMessage)

Build an array of arguments to be passed into the target listener method. Allows for multiple method arguments to be built from a single message object.

The default implementation builds an array with the given message object as sole element. This means that the extracted message will always be passed into a single method argument, even if it is an array, with the target method having a corresponding single argument of the array's type declared.

This can be overridden to treat special message content such as arrays differently, for example passing in each element of the message array as distinct method argument.

Parameters:

extractedMessage - the content of the message

Returns:

the array of arguments to be passed into the listener method (each element of the array corresponding to a distinct method argument)

invokeListenerMethod

protected Object invokeListenerMethod(String methodName,
                          Object[] arguments)
                               throws Exception

Invoke the specified listener method.

Parameters:

methodName - the name of the listener method

arguments - the message arguments to be passed in

Returns:

the result returned from the listener method

Throws:

Exception - if thrown by Rabbit API methods

See Also:

getListenerMethodName(org.springframework.amqp.core.Message, java.lang.Object), buildListenerArguments(java.lang.Object)

handleResult

protected void handleResult(Object result,
                Message request,
                com.rabbitmq.client.Channel channel)
                     throws Exception

Handle the given result object returned from the listener method, sending a response message back.

Parameters:

result - the result object to handle (never null)

request - the original request message

channel - the Rabbit channel to operate on (may be null)

Throws:

Exception - if thrown by Rabbit API methods

See Also:

buildMessage(com.rabbitmq.client.Channel, java.lang.Object), postProcessResponse(org.springframework.amqp.core.Message, org.springframework.amqp.core.Message), getReplyToAddress(Message), sendResponse(com.rabbitmq.client.Channel, org.springframework.amqp.core.Address, org.springframework.amqp.core.Message)

getReceivedExchange

protected String getReceivedExchange(Message request)

buildMessage

protected Message buildMessage(com.rabbitmq.client.Channel session,
                   Object result)
                        throws Exception

Build a Rabbit message to be sent as response based on the given result object.

Parameters:

session - the Rabbit Channel to operate on

result - the content of the message, as returned from the listener method

Returns:

the Rabbit Message (never null)

Throws:

Exception - if thrown by Rabbit API methods

See Also:

setMessageConverter(org.springframework.amqp.support.converter.MessageConverter)

postProcessResponse

protected void postProcessResponse(Message request,
                       Message response)
                            throws Exception

Post-process the given response message before it will be sent.

The default implementation sets the response's correlation id to the request message's correlation id, if any; otherwise to the request message id.

Parameters:

request - the original incoming Rabbit message

response - the outgoing Rabbit message about to be sent

Throws:

Exception - if thrown by Rabbit API methods

getReplyToAddress

protected Address getReplyToAddress(Message request)
                             throws Exception

Determine a reply-to Address for the given message.

The default implementation first checks the Rabbit Reply-To Address of the supplied request; if that is not null it is returned; if it is null, then the configured default response Exchange and routing key are used to construct a reply-to Address. If the responseExchange property is also null, then an AmqpException is thrown.

Parameters:

request - the original incoming Rabbit message

Returns:

the reply-to Address (never null)

Throws:

Exception - if thrown by Rabbit API methods

AmqpException - if no Address can be determined

See Also:

setResponseExchange(String), setResponseRoutingKey(String), Message.getMessageProperties(), MessageProperties.getReplyTo()

sendResponse

protected void sendResponse(com.rabbitmq.client.Channel channel,
                Address replyTo,
                Message message)
                     throws Exception

Send the given response message to the given destination.

Parameters:

channel - the Rabbit channel to operate on

replyTo - the Rabbit ReplyTo string to use when sending. Currently interpreted to be the routing key.

message - the Rabbit message to send

Throws:

Exception - if thrown by Rabbit API methods

See Also:

postProcessResponse(Message, Message)

postProcessChannel

protected void postProcessChannel(com.rabbitmq.client.Channel channel,
                      Message response)
                           throws Exception

Post-process the given message producer before using it to send the response.

The default implementation is empty.

Parameters:

response - the outgoing Rabbit message about to be sent

Throws:

Exception - if thrown by Rabbit API methods