org.alfresco.traitextender.SingletonExtensionFactory.java Source code

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Here is the source code for org.alfresco.traitextender.SingletonExtensionFactory.java

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/*
 * #%L
 * Alfresco Repository
 * %%
 * Copyright (C) 2005 - 2016 Alfresco Software Limited
 * %%
 * This file is part of the Alfresco software. 
 * If the software was purchased under a paid Alfresco license, the terms of 
 * the paid license agreement will prevail.  Otherwise, the software is 
 * provided under the following open source license terms:
 * 
 * Alfresco is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * Alfresco is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with Alfresco. If not, see <http://www.gnu.org/licenses/>.
 * #L%
 */

package org.alfresco.traitextender;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Creates singleton extension sub classes that are extension API implementors.
 * The singleton extensions continue to exist after the extensible has been
 * collected.
 *
 * @author Bogdan Horje
 */
public class SingletonExtensionFactory<E, S extends SingletonExtension<E, T>, T extends Trait>
        implements ExtensionFactory<E> {
    private Log logger = LogFactory.getLog(SingletonExtensionFactory.class);

    private class TraiSingletontHandler implements InvocationHandler {
        private S singleton;

        private T trait;

        public TraiSingletontHandler(S singleton, T trait) {
            super();
            this.singleton = singleton;
            this.trait = trait;
        }

        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
            // Subsequent trait calls might change the trait on this thread.
            // We save the current trait on the current call-stack in order
            // to restore it on the finally block.

            T stackedTrait = this.singleton.getTrait();

            this.singleton.setTrait(trait);
            try {
                return method.invoke(this.singleton, args);
            } catch (IllegalAccessException error) {
                throw new InvalidExtension(error);
            } catch (IllegalArgumentException error) {
                throw new InvalidExtension(error);
            } catch (InvocationTargetException error) {
                Throwable targetException = error.getTargetException();
                throw targetException;
            } finally {
                this.singleton.setTrait(stackedTrait);
            }
        }

    }

    private S singleton;

    private Class<E> extensionAPI;

    public SingletonExtensionFactory(S singleton, Class<E> extensionAPI) throws InvalidExtension {
        super();
        if (!extensionAPI.isAssignableFrom(singleton.getClass())) {
            throw new InvalidExtension(singleton.getClass() + " is not an " + extensionAPI + " extension.");
        }
        this.singleton = singleton;
        this.extensionAPI = extensionAPI;

    }

    @SuppressWarnings("unchecked")
    @Override
    public <TO extends Trait> E createExtension(TO traitObject) {
        T tTrait = (T) traitObject;
        // perform programmatic RTTI
        if (!singleton.acceptsTrait(traitObject)) {
            throw new InvalidExtension(
                    "Extension factory error : " + singleton.getClass() + " does not support trait " + traitObject);
        }

        if (logger.isDebugEnabled()) {
            String traitTrace = traitObject != null ? traitObject.getClass().toString() : "<null> trait";
            logger.info("Creating singleton extension " + singleton.getClass() + "<-" + traitTrace);
        } else {
            logger.info("Creating singleton extension " + singleton.getClass());
        }

        return (E) Proxy.newProxyInstance(getClass().getClassLoader(), new Class[] { extensionAPI },
                new TraiSingletontHandler(singleton, tTrait));
    }

    @Override
    public boolean canCreateExtensionFor(ExtensionPoint<?, ?> point) {
        return point.getExtensionAPI().isAssignableFrom(singleton.getClass())
                && singleton.acceptsTraitClass(point.getTraitAPI());
    }

}