    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
    015package org.apache.tapestry5.ioc.services;
    016
    017import 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)
    025public 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}