org.hawkular.bus.common.consumer

Class AbstractBasicMessageListener<T extends BasicMessage>

java.lang.Object

org.hawkular.bus.common.consumer.AbstractBasicMessageListener<T>

All Implemented Interfaces:

javax.jms.MessageListener

Direct Known Subclasses:

BasicMessageListener, RPCBasicMessageListener

public abstract class AbstractBasicMessageListener<T extends BasicMessage>
extends Object
implements javax.jms.MessageListener

A message listener that expects to receive a JSON-encoded BasicMessage or one of its subclasses; the JSON decoding is handled for you. Subclasses will typically override AbstractBasicMessageListener(Class) or determineBasicMessageClass() unless either (a) the subclass hierarchy has generic types that are specific enough for reflection to determine the type of BasicMessage being listened for or (b) the message type being listened for is BasicMessage and not one of its subclasses.

Constructor Summary

Constructors

Modifier	Constructor and Description
	AbstractBasicMessageListener()
protected	AbstractBasicMessageListener(Class<T> jsonDecoderRing) If a subclass knows the type and can give it to us, that will be the type used to decode JSON strings into that message type.
protected	AbstractBasicMessageListener(ClassLoader basicMessageClassLoader) A special constructor to be used when the desarialization should be based on the class name supplied in MessageProcessor.HEADER_BASIC_MESSAGE_CLASS string property of Message.

Method Summary

Modifier and Type	Method and Description
protected String	convertReceivedMessageClassNameToDesiredMessageClassName(String className) This allows subclasses to name a different JSON POJO implementation to use when deserializing incoming JSON.
protected Class<T>	determineBasicMessageClass() In order to decode the JSON, we need the class representation of the basic message type.
protected Class<T>	getBasicMessageClass()
ConsumerConnectionContext	getConsumerConnectionContext() When this listener is attached to a consumer, this field should be filled in to allow the listener to perform other tasks it needs which might require access to the context.
protected org.jboss.logging.Logger	getLog()
protected BasicMessageWithExtraData<T>	parseMessage(javax.jms.Message message) Given the BasicMessage received over the wire, convert it to our T representation of the message and keep any extra data that came with it.
void	setConsumerConnectionContext(ConsumerConnectionContext consumerConnectionContext)

Methods inherited from class java.lang.Object

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

Methods inherited from interface javax.jms.MessageListener

onMessage

Constructor Detail

AbstractBasicMessageListener

public AbstractBasicMessageListener()

AbstractBasicMessageListener

protected AbstractBasicMessageListener(Class<T> jsonDecoderRing)

If a subclass knows the type and can give it to us, that will be the type used to decode JSON strings into that message type. If this constructor is not used by subclasses, typically those subclasses will need to override determineBasicMessageClass() unless BasicMessage is the message type that subclass wants to explicitly use (as opposed to a subclass of BasicMessage).

Parameters:

jsonDecoderRing - the class representation of the generic type T

AbstractBasicMessageListener

protected AbstractBasicMessageListener(ClassLoader basicMessageClassLoader)

A special constructor to be used when the desarialization should be based on the class name supplied in MessageProcessor.HEADER_BASIC_MESSAGE_CLASS string property of Message. The given basicMessageClassLoader should be able to resolve all types of messages the present listener can encounter.

Parameters:

basicMessageClassLoader - the ClassLoader to resolve the class supplied in MessageProcessor.HEADER_BASIC_MESSAGE_CLASS string property of Message

Method Detail

getConsumerConnectionContext

public ConsumerConnectionContext getConsumerConnectionContext()

When this listener is attached to a consumer, this field should be filled in to allow the listener to perform other tasks it needs which might require access to the context.

Returns:

the consumer context this listener is associated with, or null if not associated with a consumer yet

setConsumerConnectionContext

public void setConsumerConnectionContext(ConsumerConnectionContext consumerConnectionContext)

parseMessage

protected BasicMessageWithExtraData<T> parseMessage(javax.jms.Message message)

Given the BasicMessage received over the wire, convert it to our T representation of the message and keep any extra data that came with it.

The class T is determined as follows: First, the property MessageProcessor.HEADER_BASIC_MESSAGE_CLASS is looked up in the given message's properties if there is a class name set and if basicMessageClassLoader is not null, the class is gotten using Class.forName(className, true, basicMessageClassLoader) (may throw an unchecked ClassNotFoundException), otherwise getBasicMessageClass() is used to get the Java type to deserialize to.

Parameters:

message - the over-the-wire message

Returns:

the message as a object T, or null if we should not or cannot process the message

getBasicMessageClass

protected Class<T> getBasicMessageClass()

determineBasicMessageClass

protected Class<T> determineBasicMessageClass()

In order to decode the JSON, we need the class representation of the basic message type. This method uses reflection to try to get that type. Subclasses can override this if they want to provide the class representation themselves (e.g. in case the reflection cannot get it). Alternatively, subclasses can utilize the constructor AbstractBasicMessageListener(Class) to tell this object what the class of T is.

Returns:

class of T

convertReceivedMessageClassNameToDesiredMessageClassName

protected String convertReceivedMessageClassNameToDesiredMessageClassName(String className)

This allows subclasses to name a different JSON POJO implementation to use when deserializing incoming JSON. When JSON messages are received with a classname specified as the one to deserialize the JSON, this method lets you switch the classname so it will be used to deserialize the JSON. This is helpful if the JSON classname is not available on the classloader, but the listener instead has another class that can be used to deserialize the JSON. This implementation always returns null. Subclasses are free to override.

Parameters:

className - the received JSON can be handled by this class

Returns:

if not null, this will be the name of another class that is to be used to deserialize a JSON message

getLog

protected org.jboss.logging.Logger getLog()

Returns:

logger for subclasses to use to log ad-hoc debug or trace messages