    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.beanutils2.converters;
    018
    019/**
    020 * {@link org.apache.commons.beanutils2.Converter} implementation that handles conversion to and from <strong>java.lang.Class</strong> objects.
    021 * <p>
    022 * The class will be loaded from the thread context class loader (if it exists); otherwise the class loader that loaded this class will be used.
    023 * <p>
    024 * Can be configured to either return a <em>default value</em> or throw a {@code ConversionException} if a conversion error occurs.
    025 *
    026 * @param <T> the type of the class.
    027 * @since 1.4
    028 */
    029public final class ClassConverter<T> extends AbstractConverter<Class<T>> {
    030
    031    /**
    032     * Constructs a <strong>java.lang.Class</strong> <em>Converter</em> that throws a {@code ConversionException} if an error occurs.
    033     */
    034    public ClassConverter() {
    035    }
    036
    037    /**
    038     * Constructs a <strong>java.lang.Class</strong> <em>Converter</em> that returns a default value if an error occurs.
    039     *
    040     * @param defaultValue The default value to be returned if the value to be converted is missing or an error occurs converting the value.
    041     */
    042    public ClassConverter(final Class<T> defaultValue) {
    043        super(defaultValue);
    044    }
    045
    046    /**
    047     * <p>
    048     * Converts a java.lang.Class or object into a String.
    049     * </p>
    050     *
    051     * @param value The input value to be converted
    052     * @return the converted String value.
    053     * @since 1.8.0
    054     */
    055    @Override
    056    protected String convertToString(final Object value) {
    057        return value instanceof Class ? ((Class<?>) value).getName() : value.toString();
    058    }
    059
    060    /**
    061     * <p>
    062     * Converts the input object into a java.lang.Class.
    063     * </p>
    064     *
    065     * @param <R>   Target type of the conversion.
    066     * @param type  Data type to which this value should be converted.
    067     * @param value The input value to be converted.
    068     * @return The converted value.
    069     * @throws Throwable if an error occurs converting to the specified type
    070     * @since 1.8.0
    071     */
    072    @Override
    073    protected <R> R convertToType(final Class<R> type, final Object value) throws Throwable {
    074        if (Class.class.equals(type)) {
    075            ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
    076            if (classLoader != null) {
    077                try {
    078                    return type.cast(classLoader.loadClass(value.toString()));
    079                } catch (final ClassNotFoundException ex) {
    080                    // Don't fail, carry on and try this class's class loader
    081                    // (see issue# BEANUTILS-263)
    082                }
    083            }
    084
    085            // Try this class's class loader
    086            classLoader = ClassConverter.class.getClassLoader();
    087            return type.cast(classLoader.loadClass(value.toString()));
    088        }
    089
    090        throw conversionException(type, value);
    091    }
    092
    093    /**
    094     * Gets the default type this {@code Converter} handles.
    095     *
    096     * @return The default type this {@code Converter} handles.
    097     * @since 1.8.0
    098     */
    099    @SuppressWarnings({ "unchecked", "rawtypes" })
    100    @Override
    101    protected Class<Class<T>> getDefaultType() {
    102        return (Class) Class.class;
    103    }
    104
    105}