001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.beanutils.converters;
018
019/**
020 * {@link org.apache.commons.beanutils.Converter} implementaion that handles conversion
021 * to and from <b>java.lang.Class</b> objects.
022 * <p>
023 * The class will be loaded from the thread context class
024 * loader (if it exists); otherwise the class loader that loaded this class
025 * will be used.
026 * <p>
027 * Can be configured to either return a <i>default value</i> or throw a
028 * <code>ConversionException</code> if a conversion error occurs.
029 *
030 * @version $Id$
031 * @since 1.4
032 */
033public final class ClassConverter extends AbstractConverter {
034
035    /**
036     * Construct a <b>java.lang.Class</b> <i>Converter</i> that throws
037     * a <code>ConversionException</code> if an error occurs.
038     */
039    public ClassConverter() {
040        super();
041    }
042
043    /**
044     * Construct a <b>java.lang.Class</b> <i>Converter</i> that returns
045     * a default value if an error occurs.
046     *
047     * @param defaultValue The default value to be returned
048     * if the value to be converted is missing or an error
049     * occurs converting the value.
050     */
051    public ClassConverter(final Object defaultValue) {
052        super(defaultValue);
053    }
054
055    /**
056     * Return the default type this <code>Converter</code> handles.
057     *
058     * @return The default type this <code>Converter</code> handles.
059     * @since 1.8.0
060     */
061    @Override
062    protected Class<?> getDefaultType() {
063        return Class.class;
064    }
065
066    /**
067     * <p>Convert a java.lang.Class or object into a String.</p>
068     *
069     * @param value The input value to be converted
070     * @return the converted String value.
071     * @since 1.8.0
072     */
073    @Override
074    protected String convertToString(final Object value) {
075        return (value instanceof Class) ? ((Class<?>)value).getName() : value.toString();
076    }
077
078    /**
079     * <p>Convert the input object into a java.lang.Class.</p>
080     *
081     * @param <T> Target type of the conversion.
082     * @param type Data type to which this value should be converted.
083     * @param value The input value to be converted.
084     * @return The converted value.
085     * @throws Throwable if an error occurs converting to the specified type
086     * @since 1.8.0
087     */
088    @Override
089    protected <T> T convertToType(final Class<T> type, final Object value) throws Throwable {
090        if (Class.class.equals(type)) {
091            ClassLoader classLoader = Thread.currentThread()
092                    .getContextClassLoader();
093            if (classLoader != null) {
094                try {
095                    return type.cast(classLoader.loadClass(value.toString()));
096                } catch (final ClassNotFoundException ex) {
097                    // Don't fail, carry on and try this class's class loader
098                    // (see issue# BEANUTILS-263)
099                }
100            }
101
102            // Try this class's class loader
103            classLoader = ClassConverter.class.getClassLoader();
104            return type.cast(classLoader.loadClass(value.toString()));
105        }
106
107        throw conversionException(type, value);
108    }
109
110}