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 --> String --> Long --> 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 }