TypeCoercer.java :  » Library » Tapestry » org » apache » tapestry » ioc » services » Java Open Source

// Copyright 2006, 2007 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package org.apache.tapestry.ioc.services;

/**
 * Makes use of {@link Coercion}s (via {@link CoercionTuple}s) to convert between an input value
 * (of some specific type) and a desired output type. Smart about coercing, even if it requires
 * multiple coercing steps (i.e., via an intermediate type, such as String).
 */
public interface TypeCoercer
{
    /**
     * Performs a coercion from an input type to a desired output type. When the target type is a
     * primitive, the actual conversion will be to the equivalent wrapper type. In some cases, the
     * TypeCoercer will need to search for an appropriate coercion, and may even combine existing
     * coercions to form new ones; in those cases, the results of the search are cached.
     * 
     * @param <S>
     *            source type (input)
     * @param <T>
     *            target type (output)
     * @param input
     * @param targetType
     *            defines the target type
     * @return the coerced value
     */
    <S, T> T coerce(S input, Class<T> targetType);

    /**
     * Used primarily inside test suites, this method performs the same steps as
     * {@link #coerce(Object, Class)}, but returns a string describing the series of coercision,
     * such as "Object --&gt; String --&gt; Long --&gt; Integer".
     * 
     * @param <S>
     *            source type (input)
     * @param <T>
     *            target type (output)
     * @param inputType
     *            the source coercion type (use void.class for coercions from null)
     * @param targetType
     *            defines the target type
     * @return a string identifying the series of coercions, or the empty string if no coercion is
     *         necessary
     */
    <S, T> String explain(Class<S> inputType, Class<T> targetType);

    /** Clears cached information stored by the TypeCoercer. */
    void clearCache();
}