    001    // Copyright 2006, 2007, 2008, 2010, 2011 The Apache Software Foundation
    002    //
    003    // Licensed under the Apache License, Version 2.0 (the "License");
    004    // you may not use this file except in compliance with the License.
    005    // You may obtain a copy of the License at
    006    //
    007    // http://www.apache.org/licenses/LICENSE-2.0
    008    //
    009    // Unless required by applicable law or agreed to in writing, software
    010    // distributed under the License is distributed on an "AS IS" BASIS,
    011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012    // See the License for the specific language governing permissions and
    013    // limitations under the License.
    014
    015    package org.apache.tapestry5.ioc.services;
    016
    017    import org.apache.tapestry5.ioc.annotations.UsesConfiguration;
    018
    019    /**
    020     * Makes use of {@link org.apache.tapestry5.ioc.services.Coercion}s to convert between an input value (of some specific
    021     * type) and a desired output type. Smart about coercing, even if it requires multiple coercion steps (i.e., via an
    022     * intermediate type, such as String).
    023     */
    024    @UsesConfiguration(CoercionTuple.class)
    025    public interface TypeCoercer
    026    {
    027        /**
    028         * Performs a coercion from an input type to a desired output type. When the target type is a primitive, the actual
    029         * conversion will be to the equivalent wrapper type. In some cases, the TypeCoercer will need to search for an
    030         * appropriate coercion, and may even combine existing coercions to form new ones; in those cases, the results of
    031         * the search are cached.
    032         * <p/>
    033         * The TypeCoercer also caches the results of a coercion search.
    034         *
    035         * @param <S>
    036         *            source type (input)
    037         * @param <T>
    038         *            target type (output)
    039         * @param input
    040         * @param targetType
    041         *            defines the target type
    042         * @return the coerced value
    043         * @throws RuntimeException
    044         *             if the input can not be coerced
    045         */
    046        <S, T> T coerce(S input, Class<T> targetType);
    047
    048        /**
    049         * Given a source and target type, computes the coercion that will be used.
    050         * <p>
    051         * Note: holding the returned coercion past the time when {@linkplain #clearCache() the cache is cleared} can cause
    052         * a memory leak, especially in the context of live reloading (wherein holding a reference to a single class make
    053         * keep an entire ClassLoader from being reclaimed).
    054         *
    055         * @since 5.2.0
    056         * @param <S>
    057         *            source type (input)
    058         * @param <T>
    059         *            target type (output)
    060         * @param sourceType
    061         *            type to coerce from
    062         * @param targetType
    063         *            defines the target type
    064         * @return the coercion that will ultimately be used
    065         */
    066        <S, T> Coercion<S, T> getCoercion(Class<S> sourceType, Class<T> targetType);
    067
    068        /**
    069         * Used primarily inside test suites, this method performs the same steps as {@link #coerce(Object, Class)}, but
    070         * returns a string describing the series of coercions, such as "Object --&gt; String --&gt; Long --&gt; Integer".
    071         *
    072         * @param <S>
    073         *            source type (input)
    074         * @param <T>
    075         *            target type (output)
    076         * @param sourceType
    077         *            the source coercion type (use void.class for coercions from null)
    078         * @param targetType
    079         *            defines the target type
    080         * @return a string identifying the series of coercions, or the empty string if no coercion is necessary
    081         */
    082        <S, T> String explain(Class<S> sourceType, Class<T> targetType);
    083
    084        /**
    085         * Clears cached information stored by the TypeCoercer.
    086         */
    087        void clearCache();
    088    }