org.springframework.data.keyvalue.redis.listener.adapter
Class MessageListenerAdapter

java.lang.Object
  org.springframework.data.keyvalue.redis.listener.adapter.MessageListenerAdapter

All Implemented Interfaces:

MessageListener

public class MessageListenerAdapter
extends Object
implements MessageListener

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 Redis API.

Modeled as much as possible after the JMS MessageListenerAdapter in Spring Framework.

By default, the content of incoming Redis 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 Data RedisSerializer. By default, the JdkSerializationRedisSerializer will be used. (If you do not want such automatic message conversion taking place, then be sure to set the Serializer to null.)

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.

public interface MessageContentsDelegate {
    void handleMessage(String text);
    void handleMessage(byte[] bytes);
    void handleMessage(Person obj);
 }

For further examples and discussion please do refer to the Spring Data reference documentation which describes this class (and its attendant configuration) in detail. Important: Due to the nature of messages, the default serializer used by the adapter is StringRedisSerializer. If the messages are of a different type, change them accordingly through setSerializer(RedisSerializer).

Author:

Juergen Hoeller, Costin Leau

See Also:

MessageListenerAdapter

Field Summary

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

MessageListenerAdapter()
Create a new MessageListenerAdapter with default settings.

MessageListenerAdapter(Object delegate)
Create a new MessageListenerAdapter for the given delegate.

Method Summary

protected Object[]	buildListenerArguments(Object extractedMessage) Build an array of arguments to be passed into the target listener method.
protected Object	extractMessage(Message message) Extract the message body from the given Redis message.
protected String	getDefaultListenerMethod() Return the name of the default listener method to delegate to.
Object	getDelegate() Returns 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 void	handleListenerException(Throwable ex) Handle the given exception that arose during listener execution.
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, byte[] pattern) Standard Redis MessageListener entry point.
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	setSerializer(RedisSerializer<?> serializer) Set the serializer that will convert incoming raw Redis messages to listener method arguments.

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

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 - delegate object

getDelegate

public Object getDelegate()

Returns the target object to delegate message listening to.

Returns:

message listening delegation

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.data.keyvalue.redis.connection.Message, java.lang.Object)

getDefaultListenerMethod

protected String getDefaultListenerMethod()

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

setSerializer

public void setSerializer(RedisSerializer<?> serializer)

Set the serializer that will convert incoming raw Redis messages to listener method arguments.

The default converter is a JdkSerializationRedisSerializer, which is able to handle Serializable objects.

onMessage

public void onMessage(Message message,
                      byte[] pattern)

Standard Redis 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.

Specified by:

onMessage in interface MessageListener

Parameters:

message - the incoming Redis message

pattern - pattern matching the channel (if specified) - can be null

See Also:

handleListenerException(java.lang.Throwable)

initDefaultStrategies

protected void initDefaultStrategies()

Initialize the default implementations for the adapter's strategies.

See Also:

setSerializer(RedisSerializer), JdkSerializationRedisSerializer

handleListenerException

protected void handleListenerException(Throwable ex)

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

Parameters:

ex - the exception to handle

extractMessage

protected Object extractMessage(Message message)

Extract the message body from the given Redis message.

Parameters:

message - the Redis Message

Returns:

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

getListenerMethodName

protected String getListenerMethodName(Message originalMessage,
                                       Object extractedMessage)

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 Redis request message

extractedMessage - the converted Redis 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)

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)

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

See Also:

getListenerMethodName(org.springframework.data.keyvalue.redis.connection.Message, java.lang.Object), buildListenerArguments(java.lang.Object)