abstractstatecontextlookup.java

mina是以Java实现的一个开源的网络程序框架

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 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
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 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
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 *  KIND, either express or implied.  See the License for the
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package org.apache.mina.statemachine.context;

/**
 * Abstract {@link StateContextLookup} implementation. The {@link #lookup(Object[])}
 * method will loop through the event arguments and call the {@link #supports(Class)}
 * method for each of them. The first argument that this method returns 
 * <code>true</code> for will be passed to the abstract {@link #lookup(Object)}
 * method which should try to extract a {@link StateContext} from the argument.
 * If none is found a new {@link StateContext} will be created and stored in the
 * event argument using the {@link #store(Object, StateContext)} method.
 *
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev: 589475 $, $Date: 2007-10-29 04:12:59 +0100 (Mon, 29 Oct 2007) $
 */
public abstract class AbstractStateContextLookup implements StateContextLookup {
    private final StateContextFactory contextFactory;

    /**
     * Creates a new instance which uses the specified {@link StateContextFactory}
     * to create {@link StateContext} objects.
     * 
     * @param contextFactory the factory.
     */
    public AbstractStateContextLookup(StateContextFactory contextFactory) {
        if (contextFactory == null) {
            throw new NullPointerException("contextFactory");
        }
        this.contextFactory = contextFactory;
    }
    
    public StateContext lookup(Object[] eventArgs) {
        for (int i = 0; i < eventArgs.length; i++) {
            if (supports(eventArgs[i].getClass())) {
                StateContext sc = lookup(eventArgs[i]);
                if (sc == null) {
                    sc = contextFactory.create();
                    store(eventArgs[i], sc);
                }
                return sc;
            }
        }
        return null;
    }
    
    /**
     * Extracts a {@link StateContext} from the specified event argument which
     * is an instance of a class {@link #supports(Class)} returns 
     * <code>true</code> for.
     * 
     * @param eventArg the event argument.
     * @return the {@link StateContext}.
     */
    protected abstract StateContext lookup(Object eventArg);
    
    /**
     * Stores a new {@link StateContext} in the specified event argument which
     * is an instance of a class {@link #supports(Class)} returns 
     * <code>true</code> for.
     * 
     * @param eventArg the event argument.
     * @param context the {@link StateContext} to be stored.
     */
    protected abstract void store(Object eventArg, StateContext context);

    /**
     * Must return <code>true</code> for any {@link Class} that this
     * {@link StateContextLookup} can use to store and lookup 
     * {@link StateContext} objects.
     * 
     * @param c the class.
     * @return <code>true</code> or <code>false</code>.
     */
    protected abstract boolean supports(Class<?> c);
}