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/*******************************************************************************
* Copyright (c) 2001, 2008 Oracle Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Oracle Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.jst.jsf.common.internal.strategy;
import java.util.Collections;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import org.eclipse.jst.jsf.common.JSFCommonPlugin;
import org.eclipse.jst.jsf.common.internal.policy.IIteratorPolicy;
/**
* A strategy composite that uses an iterator policy to provide the iterator
* used to decide what order to execute the strategy in.
*
* This composite represents a grouping of strategies which represent N ways
* to perform a particular calculation and which any number for those N ways
* may be applicable to any particular situation given the policy in place.
*
* By default, the first such strategy in policy order to provide the calculation
* wins and it's result is returned. You can modify the way the result is composed
* by providing your own composition strategy using the two-arg constructor.
*
*
*
* @author cbateman
*
* @param <INPUT>
* @param <OUTPUT>
* @param <RESULTTYPE>
* @param <IDTYPE>
* @param <STRATEGYTYPE>
*/
public abstract class IteratorPolicyBasedStrategyComposite<INPUT, OUTPUT, RESULTTYPE, IDTYPE, STRATEGYTYPE extends IIdentifiableStrategy<INPUT, OUTPUT, IDTYPE>>
extends StrategyComposite<INPUT, OUTPUT, RESULTTYPE, IDTYPE, STRATEGYTYPE>
{
private final Map<IDTYPE, STRATEGYTYPE> _strategies;
private IIteratorPolicy<IDTYPE> _policy;
private final Object _changeLock = new Object();
/**
* @param policy
*/
protected IteratorPolicyBasedStrategyComposite(final IIteratorPolicy<IDTYPE> policy)
{
super();
_policy = policy;
_strategies = new HashMap<IDTYPE, STRATEGYTYPE>();
}
/**
* @param policy
* @param compositionStrategy
*/
protected IteratorPolicyBasedStrategyComposite(final IIteratorPolicy<IDTYPE> policy, AbstractCompositionStrategy<INPUT, OUTPUT, RESULTTYPE, STRATEGYTYPE> compositionStrategy)
{
super(compositionStrategy);
_policy = policy;
_strategies = new HashMap<IDTYPE, STRATEGYTYPE>();
}
/**
* Add strategy if not already present.
*
* @param strategy
*/
public final void addStrategy(final STRATEGYTYPE strategy)
{
synchronized(_changeLock)
{
_strategies.put(strategy.getId(), strategy);
}
}
/**
* @param strategy
*/
public final void removeStrategy(final STRATEGYTYPE strategy)
{
synchronized(_changeLock)
{
_strategies.remove(strategy.getId());
}
}
/**
* Change the active policy used to select the order in which the composite
* calls it's child strategies.
*
* If the policy is not set, then strategies are called in
*
* @param policy
*/
public final void setPolicy(final IIteratorPolicy<IDTYPE> policy)
{
// policy may not be null
if (policy == null)
{
JSFCommonPlugin.log(new Exception("stack trace only"), "Policy can't be null"); //$NON-NLS-1$ //$NON-NLS-2$
return;
}
// protect access in case getIterator is being called simulataneously
synchronized(_changeLock)
{
_policy = policy;
}
}
@Override
public final Iterator<STRATEGYTYPE> getIterator()
{
IIteratorPolicy<IDTYPE> policy = null;
Map<IDTYPE, STRATEGYTYPE> strategies = Collections.emptyMap();
synchronized(_changeLock)
{
policy = _policy;
strategies = Collections.unmodifiableMap(new HashMap<IDTYPE, STRATEGYTYPE>(_strategies));
}
final Iterator<IDTYPE> iterator = policy.getIterator(strategies.keySet());
return new StrategyIterator<IDTYPE, STRATEGYTYPE>(strategies, iterator);
}
@Override
public abstract RESULTTYPE getNoResult();
private static class StrategyIterator<IDTYPE, STRATEGYTYPE> implements
Iterator<STRATEGYTYPE>
{
private final Map<IDTYPE, STRATEGYTYPE> _map;
private final Iterator<IDTYPE> _policyIterator;
private StrategyIterator(final Map<IDTYPE, STRATEGYTYPE> map,
final Iterator<IDTYPE> policyIterator)
{
_map = map;
_policyIterator = policyIterator;
}
public boolean hasNext()
{
return _policyIterator.hasNext();
}
public STRATEGYTYPE next()
{
IDTYPE id = _policyIterator.next();
return _map.get(id);
}
public void remove()
{
throw new UnsupportedOperationException();
}
}
}
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