org.perfectjpattern.core.api.behavioral.chainofresponsibility
Class NullHandler

java.lang.Object
  org.perfectjpattern.core.api.behavioral.chainofresponsibility.NullHandler

All Implemented Interfaces:

IHandler<Object>, ISingleton

public final class NullHandler
extends Object
implements IHandler<Object>, ISingleton

Null Object Pattern implementation of IHandler.

NullHandler is a Singleton therefore it may not be directly instantiated, neither it may be extended.

Version:

$Revision: 1.0 $ $Date: Jun 23, 2007 1:40:23 PM $

Author:

Giovanni Azua

Method Summary

boolean	canHandle(Object aRequest) Returns true if this IHandler can handle the given request, false otherwise.
static NullHandler	getInstance() Returns Singleton instance of NullHandler.
IHandler<Object>	getSuccessor() Returns the Successor handler.
void	handle(Object aRequest) Handle the given request.
void	setChainStrategy(IChainStrategy aStrategy) Set the IChainStrategy to this IHandler.
void	setSuccessor(IHandler<Object> aSuccessor) Sets the Successor element.
void	start(Object aRequest) Triggers execution of the Chain if the target Handler is the first reference, otherwise implements the decision-making regarding forwarding the request to its successor IHandler instance.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static NullHandler getInstance()

Returns Singleton instance of NullHandler.

Returns:

Singleton instance of NullHandler.

getSuccessor

public IHandler<Object> getSuccessor()
                              throws UnsupportedOperationException

Returns the Successor handler.

Specified by:

getSuccessor in interface IHandler<Object>

Returns:

Successor handler.

Throws:

UnsupportedOperationException

start

public void start(Object aRequest)
           throws IllegalArgumentException

Triggers execution of the Chain if the target Handler is the first reference, otherwise implements the decision-making regarding forwarding the request to its successor IHandler instance.

Specified by:

start in interface IHandler<Object>

Parameters:

aRequest - Context-specific request to handle.

Throws:

IllegalArgumentException - 'aRequest' must not be null.

canHandle

public boolean canHandle(Object aRequest)
                  throws IllegalArgumentException

Returns true if this IHandler can handle the given request, false otherwise.

Specified by:

canHandle in interface IHandler<Object>

Parameters:

aRequest - Context-specific request to handle.

Returns:

true if this IHandler can handle the given request, false otherwise.

Throws:

IllegalArgumentException - 'aRequest' must not be null.

handle

public void handle(Object aRequest)

Handle the given request. Implements the actual handling logic and must not contain any decision-making regarding e.g. forwarding the request.

Specified by:

handle in interface IHandler<Object>

Parameters:

aRequest - Context-specific request to handle.

setSuccessor

public void setSuccessor(IHandler<Object> aSuccessor)
                  throws UnsupportedOperationException

Sets the Successor element.

Specified by:

setSuccessor in interface IHandler<Object>

Parameters:

aSuccessor - Successor handler

Throws:

UnsupportedOperationException

setChainStrategy

public void setChainStrategy(IChainStrategy aStrategy)
                      throws IllegalArgumentException

Set the IChainStrategy to this IHandler. IChainStrategy allows to easily modify how the Chain should behave. Possible implementations are e.g.

• Halt as soon as the first Handler processes the request
• Let all handlers process the request
• Let the first N handlers process the request

Specified by:

setChainStrategy in interface IHandler<Object>

Parameters:

aStrategy - Continuation strategy defines how the chain should behave

Throws:

IllegalArgumentException - 'aStrategy' must not be null.