001/*****************************************************************************
002 * Copyright (c) PicoContainer Organization. All rights reserved.            *
003 * ------------------------------------------------------------------------- *
004 * The software in this package is published under the terms of the BSD      *
005 * style license a copy of which has been included with this distribution in *
006 * the LICENSE.txt file.                                                     *
007 *                                                                           *
008 * Original code by Joerg Schaible                                           *
009 *****************************************************************************/
010
011package org.picocontainer.gems.adapters;
012
013import com.thoughtworks.proxy.ProxyFactory;
014import com.thoughtworks.proxy.factory.StandardProxyFactory;
015
016import org.picocontainer.ComponentAdapter;
017import org.picocontainer.Parameter;
018import org.picocontainer.PicoCompositionException;
019import org.picocontainer.ComponentMonitor;
020import org.picocontainer.behaviors.Cached;
021import org.picocontainer.behaviors.AbstractBehaviorFactory;
022import org.picocontainer.ComponentFactory;
023import org.picocontainer.LifecycleStrategy;
024import org.picocontainer.references.ThreadLocalReference;
025
026import java.util.Properties;
027
028
029/**
030 * A {@link ComponentFactory} for components kept in {@link ThreadLocal} instances.
031 * <p>
032 * This factory has two operating modes. By default it ensures, that every thread uses its own component at any time.
033 * This mode ({@link #ENSURE_THREAD_LOCALITY}) makes internal usage of a {@link ThreadLocalized}. If the
034 * application architecture ensures, that the thread that creates the component is always also the thread that is th
035 * only user, you can set the mode {@link #THREAD_ENSURES_LOCALITY}. In this mode the factory uses a simple
036 * {@link Cached} that uses a {@link ThreadLocalReference} to cache the component.
037 * </p>
038 * <p>
039 * See the use cases for the subtile difference:
040 * </p>
041 * <p>
042 * <code>THREAD_ENSURES_LOCALITY</code> is applicable, if the pico container is requested for a thread local addComponent
043 * from the working thread e.g. in a web application for a request. In this environment it is ensured, that the request
044 * is processed from the same thread and the thread local component is reused, if a previous request was handled in the
045 * same thread. Note that thi scenario fails badly, if the thread local component is created because of another cached
046 * component indirectly by a dependecy. In this case the cached component already have an instance of the thread local
047 * component, that may have been created in another thread, since only the component adapter for the thread local
048 * component can ensure a unique component for each thread.
049 * </p>
050 * <p>
051 * <code>ENSURES_THREAD_LOCALITY</code> solves this problem. In this case the returned component is just a proxy for
052 * the thread local component and this proxy ensures, that a new component is created for each thread. Even if another
053 * cached component has an indirect dependency on the thread local component, the proxy ensures unique instances. This
054 * is vital for a multithreaded application that uses EJBs.
055 * </p>
056 * @author J&ouml;rg Schaible
057 */
058@SuppressWarnings("serial")
059public final class ThreadLocalizing extends AbstractBehaviorFactory {
060
061
062        /**
063     * <code>ENSURE_THREAD_LOCALITY</code> is the constant for created {@link ComponentAdapter} instances, that ensure
064     * unique instances of the component by delivering a proxy for the component.
065     */
066    public static final boolean ENSURE_THREAD_LOCALITY = true;
067    /**
068     * <code>THREAD_ENSURES_LOCALITY</code> is the constant for created {@link ComponentAdapter} instances, that
069     * create for the current thread a new component.
070     */
071    public static final boolean THREAD_ENSURES_LOCALITY = false;
072
073    private final boolean ensureThreadLocal;
074    private final ProxyFactory proxyFactory;
075
076    /**
077     * Constructs a wrapping ThreadLocalizing, that ensures the usage of the ThreadLocal. The Proxy
078     * instances are generated by the JDK.
079     */
080    public ThreadLocalizing() {
081        this(new StandardProxyFactory());
082    }
083
084    /**
085     * Constructs a wrapping ThreadLocalizing, that ensures the usage of the ThreadLocal.
086     * @param proxyFactory The {@link ProxyFactory} to use.
087     */
088    public ThreadLocalizing(final ProxyFactory proxyFactory) {
089        this(ENSURE_THREAD_LOCALITY, proxyFactory);
090    }
091
092    /**
093     * Constructs a wrapping ThreadLocalizing.
094     * @param ensure {@link #ENSURE_THREAD_LOCALITY} or {@link #THREAD_ENSURES_LOCALITY}.
095     */
096    public ThreadLocalizing(final boolean ensure) {
097        this(ensure, new StandardProxyFactory());
098    }
099
100    /**
101     * Constructs a wrapping ThreadLocalizing.
102     * @param ensure {@link #ENSURE_THREAD_LOCALITY} or {@link #THREAD_ENSURES_LOCALITY}.
103     * @param factory The {@link ProxyFactory} to use.
104     */
105    protected ThreadLocalizing(
106            final boolean ensure, final ProxyFactory factory) {
107        ensureThreadLocal = ensure;
108        proxyFactory = factory;
109    }
110
111    @Override
112        public ComponentAdapter createComponentAdapter(
113            final ComponentMonitor componentMonitor, final LifecycleStrategy lifecycleStrategy, final Properties componentProperties, final Object componentKey, final Class componentImplementation, final Parameter... parameters)
114            throws PicoCompositionException
115    {
116        final ComponentAdapter componentAdapter;
117        if (ensureThreadLocal) {
118            componentAdapter = new ThreadLocalized(super.createComponentAdapter(
119                    componentMonitor, lifecycleStrategy, componentProperties, componentKey, componentImplementation, parameters), proxyFactory);
120        } else {
121            componentAdapter = new Cached(super.createComponentAdapter(
122                    componentMonitor, lifecycleStrategy, componentProperties, componentKey, componentImplementation, parameters), new ThreadLocalReference());
123        }
124        return componentAdapter;
125    }
126
127
128    @Override
129        public ComponentAdapter addComponentAdapter(final ComponentMonitor componentMonitor,
130                                                final LifecycleStrategy lifecycleStrategy,
131                                                final Properties componentProperties,
132                                                final ComponentAdapter adapter) {
133        if (ensureThreadLocal) {
134            return componentMonitor.newBehavior(new ThreadLocalized(super.addComponentAdapter(componentMonitor,
135                                                                     lifecycleStrategy,
136                                                                     componentProperties,
137                                                                     adapter), proxyFactory));
138        } else {
139            return componentMonitor.newBehavior(new Cached(super.addComponentAdapter(componentMonitor,
140                                                                 lifecycleStrategy,
141                                                                 componentProperties,
142                                                                 adapter), new ThreadLocalReference()));
143        }
144
145    }
146}