    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    package org.picocontainer;
    009
    010    import java.lang.reflect.Type;
    011
    012    /**
    013     * A component adapter is responsible for providing a specific component
    014     * instance of type &lt;T&gt;. An instance of an implementation of this interface is
    015     * used inside a {@link PicoContainer} for every registered component or
    016     * instance. Each <code>ComponentAdapter</code> instance has to have a key
    017     * which is unique within that container. The key itself is either a class type
    018     * (normally an interface) or an identifier.
    019     * <p>In a overly simplistic sense, the ComponentAdapter can be thought of us a type of
    020     * an object factory.  If you need to modify how your object is constructed, use and appropriate
    021     * ComponentAdapter or roll your own since the API is purposely kept rather simple.  See
    022     * <a href="http://www.picocontainer.org/adapters.html">http://www.picocontainer.org/adapters.html</a>
    023     * for more information.</p>
    024     *
    025     * @author Jon Tirs&eacute;n
    026     * @author Paul Hammant
    027     * @author Aslak Helles&oslash;y
    028     */
    029    public interface ComponentAdapter<T> {
    030
    031        public class NOTHING {
    032            private NOTHING(){
    033            }
    034        };
    035
    036        /**
    037         * Retrieve the key associated with the component.
    038         *
    039         * @return the component's key. Should either be a class type (normally an interface) or an identifier that is
    040         *         unique (within the scope of the current PicoContainer).
    041         */
    042        Object getComponentKey();
    043
    044        /**
    045         * Retrieve the class of the component.
    046         *
    047         * @return the component's implementation class. Should normally be a concrete class (ie, a class that can be
    048         *         instantiated).
    049         */
    050        Class<T> getComponentImplementation();
    051
    052        /**
    053         * Retrieve the component instance. This method will usually create a new instance each time it is called, but that
    054         * is not required. For example, {@link org.picocontainer.behaviors.Cached} will always return the
    055         * same instance.
    056         *
    057         * @param container the {@link PicoContainer}, that is used to resolve any possible dependencies of the instance.
    058         * @return the component instance.
    059         * @throws PicoCompositionException  if the component has dependencies which could not be resolved, or
    060         *                                     instantiation of the component lead to an ambigous situation within the
    061         *                                     container.
    062         * @deprecated since PicoContainer 2.2.  Use {@link getComponentInstance(PicoContainer,Type)} with {@link ComponentAdapter.NOTHING.class} as type
    063         * if no type available.
    064         */
    065        T getComponentInstance(PicoContainer container) throws PicoCompositionException;
    066
    067        /**
    068         * Retrieve the component instance. This method will usually create a new instance each time it is called, but that
    069         * is not required. For example, {@link org.picocontainer.behaviors.Cached} will always return the
    070         * same instance.
    071         *
    072         * @param container the {@link org.picocontainer.PicoContainer}, that is used to resolve any possible dependencies of the instance.
    073         * @param into the class that is about to be injected into. Use ComponentAdapter.NOTHING.class if this is not important to you.
    074         * @return the component instance.
    075         * @throws PicoCompositionException  if the component has dependencies which could not be resolved, or
    076         *                                     instantiation of the component lead to an ambiguous situation within the
    077         *                                     container.
    078         */
    079        T getComponentInstance(PicoContainer container, Type into) throws PicoCompositionException;
    080
    081        /**
    082         * Verify that all dependencies for this adapter can be satisfied. Normally, the adapter should verify this by
    083         * checking that the associated PicoContainer contains all the needed dependencies.
    084         *
    085         * @param container the {@link PicoContainer}, that is used to resolve any possible dependencies of the instance.
    086         * @throws PicoCompositionException if one or more dependencies cannot be resolved.
    087         */
    088        void verify(PicoContainer container) throws PicoCompositionException;
    089
    090        /**
    091         * Accepts a visitor for this ComponentAdapter. The method is normally called by visiting a {@link PicoContainer}, that
    092         * cascades the visitor also down to all its ComponentAdapter instances.
    093         *
    094         * @param visitor the visitor.
    095         */
    096        void accept(PicoVisitor visitor);
    097
    098        /**
    099         * Component adapters may be nested in a chain, and this method is used to grab the next ComponentAdapter in the chain.
    100         * @return the next component adapter in line or null if there is no delegate ComponentAdapter.
    101         */
    102        ComponentAdapter<T> getDelegate();
    103
    104        /**
    105         * Locates a component adapter of type <em>componentAdapterType</em> in the ComponentAdapter chain.  Will return null
    106         * if there is no adapter of the given type.
    107         * @param <U> the type of ComponentAdapter being located.
    108         * @param componentAdapterType the class of the adapter type being located.  Never null.
    109         * @return the appropriate component adapter of type <em>U</em>.  May return null if the component adapter type is not
    110         * returned.
    111         */
    112        <U extends ComponentAdapter> U findAdapterOfType(Class<U> adapterType);
    113
    114        /**
    115         * Get a string key descriptor of the component adapter.
    116         * @return
    117         */
    118        String getDescriptor();
    119
    120    }