dk.rode.thesis.chainofresponsibility
Class StandardHandlerChain<R>

java.lang.Object
  dk.rode.thesis.chainofresponsibility.AbstractHandlerChain<R>
      dk.rode.thesis.chainofresponsibility.StandardHandlerChain<R>

Type Parameters:

R - The type of requests handled by this chain.

All Implemented Interfaces:

Handler<R>, HandlerChain<R>, HandlerLink<R>

public class StandardHandlerChain<R>
extends AbstractHandlerChain<R>

A standard handler chain is the standard implementation of the HandlerChain interface.

A standard handler chain is not thread safe.

Author:

Gunni Rode / rode.dk

See Also:

WeakHandlerChain

Field Summary

private LinkedHashSet<Handler<R>>

handlers The ordered list of handlers, where the first handler is the first inserted element.

Constructor Summary

StandardHandlerChain()
No-arg constructor.

Method Summary

List<Handler<R>>	getHandlers(Handler<R> handler) Returns an ordered list of the handlers currently associated with this chain, starting from the handler after handler, if supplied.
boolean	isRegistered(Handler<R> handler) Returns true if handler is registered to this handler chain, false if not.
void	register(Handler<R> handler) Registers the handler supplied as handler to this handler chain.
int	size() Return the size of this handler chain.
void	unregister(Handler<R> handler) Removes the handler supplied as handler from this handler chain.

Methods inherited from class dk.rode.thesis.chainofresponsibility.AbstractHandlerChain

forward, handle, handle, toString

Methods inherited from class java.lang.Object

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

Field Detail

handlers

private final LinkedHashSet<Handler<R>> handlers

The ordered list of handlers, where the first handler is the first inserted element.

Implementation notes:
For small chains, a simple list will suffice, but it does not scale well: if each handler starting from handler m in the chain reinvokes the chain, we get a running time of O(n*m), i.e. worst time O(n*n), where n is the chain length. Existence, registration, and unregistration takes O(n).

A better solution is to use a linked hash set to avoid O(n) existence, registration, and unregistration time. This is the implementation here.

An even faster and more scalable solution would be to use an index into a list, pointing to the start of the sub-list to return. A navigable map (tree map) can be used for this, i.e. tailMap(..) methods. For this simple example, we are satisfied with our simple solution.

Never null.

Constructor Detail

StandardHandlerChain

public StandardHandlerChain()

No-arg constructor.

Method Detail

getHandlers

public List<Handler<R>> getHandlers(Handler<R> handler)

Description copied from interface: HandlerChain

Returns an ordered list of the handlers currently associated with this chain, starting from the handler after handler, if supplied.

If handler is null, the entire list of handlers is returned. If handler is not registered to this chain, the entire list of handlers is returned.

Modifying the returned list will not affect this chain.

Parameters:

handler - The handler to start from; can be null.

Returns:

The ordered list of handlers, starting after handler; never null, but can be empty.

isRegistered

public boolean isRegistered(Handler<R> handler)

Description copied from interface: HandlerChain

Returns true if handler is registered to this handler chain, false if not.

Parameters:

handler - The handler to test; cannot be null.

Returns:

True if registered, false if not.

register

public void register(Handler<R> handler)

Description copied from interface: HandlerChain

Registers the handler supplied as handler to this handler chain.

Registering the same handler twice is an error.

Parameters:

handler - The handler to add; cannot be null.

See Also:

HandlerChain.unregister(Handler)

size

public int size()

Description copied from interface: HandlerChain

Return the size of this handler chain.

Returns:

The size.

unregister

public void unregister(Handler<R> handler)

Description copied from interface: HandlerChain

Removes the handler supplied as handler from this handler chain.

Trying to remove a handler that is not associated with this handler chain is an error.

Parameters:

handler - The handler to remove; cannot be null.

See Also:

HandlerChain.register(Handler)