001    // Copyright 2004, 2005 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.tapestry.coerce;
016    
017    /**
018     * Converts a value (possibly null) to an alternate data type; typically from String to boolean or a
019     * number type.
020     * <p>
021     * Typically, a ValueConverter will select a particular
022     * {@link org.apache.tapestry.coerce.TypeConverter}to perform the conversion. The
023     * {@link org.apache.tapestry.coerce.ValueConverterImpl}implementation also makes use of built-in
024     * {@link java.beans.PropertyEditor}s.
025     * 
026     * @author Howard M. Lewis Ship
027     * @since 4.0
028     */
029    public interface ValueConverter
030    {
031        /**
032         * Performs a conversion of a value to a particular type.
033         * 
034         * @param value
035         *            The value to be converted (may be null)
036         * @param desiredType
037         *            the type that will be converted to
038         * @returns the value converted to the indicated type. May return the input value if it is
039         *          already assignable to the desiredType.
040         * @throws org.apache.hivemind.ApplicationRuntimeException
041         *             if the value can not be converted
042         */
043        Object coerceValue(Object value, Class desiredType);
044    }