org.springframework.amqp.rabbit.listener.adapter

Class MessageListenerAdapter

java.lang.Object

org.springframework.amqp.rabbit.listener.adapter.AbstractAdaptableMessageListener

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

All Implemented Interfaces:

MessageListener, ChannelAwareMessageListener

public class MessageListenerAdapter
extends AbstractAdaptableMessageListener

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, Cai Kun

See Also:

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

Nested Class Summary

Nested classes/interfaces inherited from class org.springframework.amqp.rabbit.listener.adapter.AbstractAdaptableMessageListener

AbstractAdaptableMessageListener.ReplyExpressionRoot

Field Summary

Fields

Modifier and Type	Field and Description
static String	ORIGINAL_DEFAULT_LISTENER_METHOD Out-of-the-box value for the default listener method: "handleMessage".

Fields inherited from class org.springframework.amqp.rabbit.listener.adapter.AbstractAdaptableMessageListener

logger

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

Modifier and Type	Method and Description
void	addQueueOrTagToMethodName(String queueOrTag, String methodName) Add the mapping of a queue name or consumer tag to a method name.
protected Object[]	buildListenerArguments(Object extractedMessage) Deprecated. use @buildListenerArguments(Object, Channel, Message) to get complete arguments
protected Object[]	buildListenerArguments(Object extractedMessage, com.rabbitmq.client.Channel channel, Message message) Build an array of arguments to be passed into the target listener method.
protected String	getDefaultListenerMethod()
protected Object	getDelegate()
protected String	getListenerMethodName(Message originalMessage, Object extractedMessage) Determine the name of the listener method that will handle the given message.
protected Object	invokeListenerMethod(String methodName, Object[] arguments, Message originalMessage) Invoke the specified listener method.
void	onMessage(Message message, com.rabbitmq.client.Channel channel) Spring ChannelAwareMessageListener entry point.
String	removeQueueOrTagToMethodName(String queueOrTag) Remove the mapping of a queue name or consumer tag to a method name.
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	setQueueOrTagToMethodName(Map<String,String> queueOrTagToMethodName) Set the mapping of queue name or consumer tag to method name.

Methods inherited from class org.springframework.amqp.rabbit.listener.adapter.AbstractAdaptableMessageListener

buildMessage, containerAckMode, doHandleResult, doPublish, extractMessage, getEncoding, getMessageConverter, getReceivedExchange, getReplyToAddress, handleListenerException, handleResult, handleResult, postProcessChannel, postProcessResponse, sendResponse, setBeanResolver, setBeforeSendReplyPostProcessors, setDefaultRequeueRejected, setEncoding, setMandatoryPublish, setMessageConverter, setRecoveryCallback, setResponseAddress, setResponseExchange, setResponseRoutingKey, setRetryTemplate

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.springframework.amqp.rabbit.listener.api.ChannelAwareMessageListener

onMessage, onMessageBatch

Methods inherited from interface org.springframework.amqp.core.MessageListener

onMessageBatch

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

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.

Parameters:

delegate - The delegate listener or POJO.

getDelegate

protected Object getDelegate()

Returns:

The target object to delegate message listening to.

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".

Parameters:

defaultListenerMethod - The name of the default listener method.

See Also:

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

getDefaultListenerMethod

protected String getDefaultListenerMethod()

Returns:

The name of the default listener method to delegate to.

setQueueOrTagToMethodName

public void setQueueOrTagToMethodName(Map<String,String> queueOrTagToMethodName)

Set the mapping of queue name or consumer tag to method name. The first lookup is by queue name, if that returns null, we lookup by consumer tag, if that returns null, the defaultListenerMethod is used.

Parameters:

queueOrTagToMethodName - the map.

Since:

1.5

addQueueOrTagToMethodName

public void addQueueOrTagToMethodName(String queueOrTag,
                                      String methodName)

Add the mapping of a queue name or consumer tag to a method name. The first lookup is by queue name, if that returns null, we lookup by consumer tag, if that returns null, the defaultListenerMethod is used.

Parameters:

queueOrTag - The queue name or consumer tag.

methodName - The method name.

Since:

1.5

removeQueueOrTagToMethodName

public String removeQueueOrTagToMethodName(String queueOrTag)

Remove the mapping of a queue name or consumer tag to a method name.

Parameters:

queueOrTag - The queue name or consumer tag.

Returns:

the method name that was removed, or null.

Since:

1.5

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.

Parameters:

message - the incoming Rabbit message

channel - the Rabbit channel to operate on

Throws:

Exception - if thrown by Rabbit API methods

getListenerMethodName

protected String getListenerMethodName(Message originalMessage,
                                       Object extractedMessage)

Determine the name of the listener method that will handle the given message.

The default implementation first consults the queueOrTagToMethodName map looking for a match on the consumer queue or consumer tag; if no match found, it simply returns the configured default listener method, or "handleMessage" if not configured.

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)

See Also:

setDefaultListenerMethod(java.lang.String), setQueueOrTagToMethodName(java.util.Map<java.lang.String, java.lang.String>)

buildListenerArguments

@Deprecated
protected Object[] buildListenerArguments(Object extractedMessage)

Deprecated. use @buildListenerArguments(Object, Channel, Message) to get complete arguments

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)

buildListenerArguments

protected Object[] buildListenerArguments(Object extractedMessage,
                                          com.rabbitmq.client.Channel channel,
                                          Message message)

Build an array of arguments to be passed into the target listener method. Allows for multiple method arguments to be built from message object with channel, More detail about extractedMessage in the method buildListenerArguments(java.lang.Object). This can be overridden to treat special message content such as arrays differently, and add argument in case of receiving Channel and original Message object to invoke basicAck method in the listener by manual acknowledge mode.

Parameters:

extractedMessage - the content of the message

channel - the Rabbit channel to operate on

message - the incoming Rabbit 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,
                                      Message originalMessage)

Invoke the specified listener method.

Parameters:

methodName - the name of the listener method

arguments - the message arguments to be passed in

originalMessage - the original message

Returns:

the result returned from the listener method

See Also:

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