    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.configuration2.convert;
    018
    019import java.lang.reflect.Array;
    020import java.util.Collection;
    021import java.util.Iterator;
    022import java.util.LinkedList;
    023
    024import org.apache.commons.configuration2.ex.ConversionException;
    025import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
    026import org.apache.commons.lang3.ClassUtils;
    027
    028/**
    029 * <p>
    030 * A default implementation of the {@code ConversionHandler} interface.
    031 * </p>
    032 * <p>
    033 * This class implements the standard data type conversions as used by {@code AbstractConfiguration} and derived
    034 * classes. There is a central conversion method - {@code convert()} - for converting a passed in object to a given
    035 * target class. The basic implementation already handles a bunch of standard data type conversions. If other
    036 * conversions are to be supported, this method can be overridden.
    037 * </p>
    038 * <p>
    039 * The object passed to {@code convert()} can be a single value or a complex object (like an array, a collection, etc.)
    040 * containing multiple values. It lies in the responsibility of {@code convert()} to deal with such complex objects. The
    041 * implementation provided by this class tries to extract the first child element and then delegates to
    042 * {@code convertValue()} which does the actual conversion.
    043 * </p>
    044 *
    045 * @since 2.0
    046 */
    047public class DefaultConversionHandler implements ConversionHandler {
    048    /**
    049     * A default instance of this class. Because an instance of this class can be shared between arbitrary objects it is
    050     * possible to make use of this default instance anywhere.
    051     */
    052    public static final DefaultConversionHandler INSTANCE = new DefaultConversionHandler();
    053
    054    /** The default format for dates. */
    055    public static final String DEFAULT_DATE_FORMAT = "yyyy-MM-dd HH:mm:ss";
    056
    057    /** A helper object used for extracting values from complex objects. */
    058    private static final AbstractListDelimiterHandler EXTRACTOR = (AbstractListDelimiterHandler) DisabledListDelimiterHandler.INSTANCE;
    059
    060    /**
    061     * Constant for a default {@code ConfigurationInterpolator} to be used if none is provided by the caller.
    062     */
    063    private static final ConfigurationInterpolator NULL_INTERPOLATOR = new ConfigurationInterpolator() {
    064        @Override
    065        public Object interpolate(final Object value) {
    066            return value;
    067        }
    068    };
    069
    070    /** The current date format. */
    071    private volatile String dateFormat;
    072
    073    /**
    074     * Returns the date format used by this conversion handler.
    075     *
    076     * @return the date format
    077     */
    078    public String getDateFormat() {
    079        final String fmt = dateFormat;
    080        return fmt != null ? fmt : DEFAULT_DATE_FORMAT;
    081    }
    082
    083    /**
    084     * Sets the date format to be used by this conversion handler. This format is applied by conversions to {@code Date} or
    085     * {@code Calendar} objects. The string is passed to the {@code java.text.SimpleDateFormat} class, so it must be
    086     * compatible with this class. If no date format has been set, a default format is used.
    087     *
    088     * @param dateFormat the date format string
    089     * @see #DEFAULT_DATE_FORMAT
    090     */
    091    public void setDateFormat(final String dateFormat) {
    092        this.dateFormat = dateFormat;
    093    }
    094
    095    @Override
    096    public <T> T to(final Object src, final Class<T> targetCls, final ConfigurationInterpolator ci) {
    097        final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
    098        return convert(interpolator.interpolate(src), targetCls, interpolator);
    099    }
    100
    101    /**
    102     * {@inheritDoc} This implementation extracts all values stored in the passed in source object, converts them to the
    103     * target type, and adds them to a result array. Arrays of objects and of primitive types are supported. If the source
    104     * object is <b>null</b>, result is <b>null</b>, too.
    105     */
    106    @Override
    107    public Object toArray(final Object src, final Class<?> elemClass, final ConfigurationInterpolator ci) {
    108        if (src == null) {
    109            return null;
    110        }
    111        if (isEmptyElement(src)) {
    112            return Array.newInstance(elemClass, 0);
    113        }
    114
    115        final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
    116        return elemClass.isPrimitive() ? toPrimitiveArray(src, elemClass, interpolator) : toObjectArray(src, elemClass, interpolator);
    117    }
    118
    119    /**
    120     * {@inheritDoc} This implementation extracts all values stored in the passed in source object, converts them to the
    121     * target type, and adds them to the target collection. The target collection must not be <b>null</b>. If the source
    122     * object is <b>null</b>, nothing is added to the collection.
    123     *
    124     * @throws IllegalArgumentException if the target collection is <b>null</b>
    125     */
    126    @Override
    127    public <T> void toCollection(final Object src, final Class<T> elemClass, final ConfigurationInterpolator ci, final Collection<T> dest) {
    128        if (dest == null) {
    129            throw new IllegalArgumentException("Target collection must not be null!");
    130        }
    131
    132        if (src != null && !isEmptyElement(src)) {
    133            final ConfigurationInterpolator interpolator = fetchInterpolator(ci);
    134            convertToCollection(src, elemClass, interpolator, dest);
    135        }
    136    }
    137
    138    /**
    139     * Tests whether the passed in object is complex (which means that it contains multiple values). This method is called
    140     * by {@link #convert(Object, Class, ConfigurationInterpolator)} to figure out whether a actions are required to extract
    141     * a single value from a complex source object. This implementation considers the following objects as complex:
    142     * <ul>
    143     * <li>{@code Iterable} objects</li>
    144     * <li>{@code Iterator} objects</li>
    145     * <li>Arrays</li>
    146     * </ul>
    147     *
    148     * @param src the source object
    149     * @return <b>true</b> if this is a complex object, <b>false</b> otherwise
    150     */
    151    protected boolean isComplexObject(final Object src) {
    152        return src instanceof Iterator<?> || src instanceof Iterable<?> || (src != null && src.getClass().isArray());
    153    }
    154
    155    /**
    156     * Tests whether the passed in object represents an empty element. This method is called by conversion methods to arrays
    157     * or collections. If it returns <b>true</b>, the resulting array or collection will be empty. This implementation
    158     * returns <b>true</b> if and only if the passed in object is an empty string. With this method it can be controlled if
    159     * and how empty elements in configurations are handled.
    160     *
    161     * @param src the object to be tested
    162     * @return a flag whether this object is an empty element
    163     */
    164    protected boolean isEmptyElement(final Object src) {
    165        return (src instanceof CharSequence) && ((CharSequence) src).length() == 0;
    166    }
    167
    168    /**
    169     * Performs the conversion from the passed in source object to the specified target class. This method is called for
    170     * each conversion to be done. The source object has already been passed to the {@link ConfigurationInterpolator}, so
    171     * interpolation does not have to be done again. (The passed in {@code ConfigurationInterpolator} may still be necessary
    172     * for extracting values from complex objects; it is guaranteed to be non <b>null</b>.) The source object may be a
    173     * complex object, e.g. a collection or an array. This base implementation checks whether the source object is complex.
    174     * If so, it delegates to {@link #extractConversionValue(Object, Class, ConfigurationInterpolator)} to obtain a single
    175     * value. Eventually, {@link #convertValue(Object, Class, ConfigurationInterpolator)} is called with the single value to
    176     * be converted.
    177     *
    178     * @param <T> the desired target type of the conversion
    179     * @param src the source object to be converted
    180     * @param targetCls the desired target class
    181     * @param ci the {@code ConfigurationInterpolator} (not <b>null</b>)
    182     * @return the converted value
    183     * @throws ConversionException if conversion is not possible
    184     */
    185    protected <T> T convert(final Object src, final Class<T> targetCls, final ConfigurationInterpolator ci) {
    186        final Object conversionSrc = isComplexObject(src) ? extractConversionValue(src, targetCls, ci) : src;
    187        return convertValue(ci.interpolate(conversionSrc), targetCls, ci);
    188    }
    189
    190    /**
    191     * Extracts a maximum number of values contained in the given source object and returns them as flat collection. This
    192     * method is useful if the caller only needs a subset of values, e.g. only the first one.
    193     *
    194     * @param source the source object (may be a single value or a complex object)
    195     * @param limit the number of elements to extract
    196     * @return a collection with all extracted values
    197     */
    198    protected Collection<?> extractValues(final Object source, final int limit) {
    199        return EXTRACTOR.flatten(source, limit);
    200    }
    201
    202    /**
    203     * Extracts all values contained in the given source object and returns them as a flat collection.
    204     *
    205     * @param source the source object (may be a single value or a complex object)
    206     * @return a collection with all extracted values
    207     */
    208    protected Collection<?> extractValues(final Object source) {
    209        return extractValues(source, Integer.MAX_VALUE);
    210    }
    211
    212    /**
    213     * Extracts a single value from a complex object. This method is called by {@code convert()} if the source object is
    214     * complex. This implementation extracts the first value from the complex object and returns it.
    215     *
    216     * @param container the complex object
    217     * @param targetCls the target class of the conversion
    218     * @param ci the {@code ConfigurationInterpolator} (not <b>null</b>)
    219     * @return the value to be converted (may be <b>null</b> if no values are found)
    220     */
    221    protected Object extractConversionValue(final Object container, final Class<?> targetCls, final ConfigurationInterpolator ci) {
    222        final Collection<?> values = extractValues(container, 1);
    223        return values.isEmpty() ? null : ci.interpolate(values.iterator().next());
    224    }
    225
    226    /**
    227     * Performs a conversion of a single value to the specified target class. The passed in source object is guaranteed to
    228     * be a single value, but it can be <b>null</b>. Derived classes that want to extend the available conversions, but are
    229     * happy with the handling of complex objects, just need to override this method.
    230     *
    231     * @param <T> the desired target type of the conversion
    232     * @param src the source object (a single value)
    233     * @param targetCls the target class of the conversion
    234     * @param ci the {@code ConfigurationInterpolator} (not <b>null</b>)
    235     * @return the converted value
    236     * @throws ConversionException if conversion is not possible
    237     */
    238    protected <T> T convertValue(final Object src, final Class<T> targetCls, final ConfigurationInterpolator ci) {
    239        if (src == null) {
    240            return null;
    241        }
    242
    243        // This is a safe cast because PropertyConverter either returns an
    244        // object of the correct class or throws an exception.
    245        @SuppressWarnings("unchecked")
    246        final T result = (T) PropertyConverter.to(targetCls, src, this);
    247        return result;
    248    }
    249
    250    /**
    251     * Converts the given source object to an array of objects.
    252     *
    253     * @param src the source object
    254     * @param elemClass the element class of the array
    255     * @param ci the {@code ConfigurationInterpolator}
    256     * @return the result array
    257     * @throws ConversionException if a conversion cannot be performed
    258     */
    259    private <T> T[] toObjectArray(final Object src, final Class<T> elemClass, final ConfigurationInterpolator ci) {
    260        final Collection<T> convertedCol = new LinkedList<>();
    261        convertToCollection(src, elemClass, ci, convertedCol);
    262        // Safe to cast because the element class is specified
    263        @SuppressWarnings("unchecked")
    264        final T[] result = (T[]) Array.newInstance(elemClass, convertedCol.size());
    265        return convertedCol.toArray(result);
    266    }
    267
    268    /**
    269     * Converts the given source object to an array of a primitive type. This method performs some checks whether the source
    270     * object is already an array of the correct type or a corresponding wrapper type. If not, all values are extracted,
    271     * converted one by one, and stored in a newly created array.
    272     *
    273     * @param src the source object
    274     * @param elemClass the element class of the array
    275     * @param ci the {@code ConfigurationInterpolator}
    276     * @return the result array
    277     * @throws ConversionException if a conversion cannot be performed
    278     */
    279    private Object toPrimitiveArray(final Object src, final Class<?> elemClass, final ConfigurationInterpolator ci) {
    280        if (src.getClass().isArray()) {
    281            if (src.getClass().getComponentType().equals(elemClass)) {
    282                return src;
    283            }
    284
    285            if (src.getClass().getComponentType().equals(ClassUtils.primitiveToWrapper(elemClass))) {
    286                // the value is an array of the wrapper type derived from the
    287                // specified primitive type
    288                final int length = Array.getLength(src);
    289                final Object array = Array.newInstance(elemClass, length);
    290
    291                for (int i = 0; i < length; i++) {
    292                    Array.set(array, i, Array.get(src, i));
    293                }
    294                return array;
    295            }
    296        }
    297
    298        final Collection<?> values = extractValues(src);
    299        final Class<?> targetClass = ClassUtils.primitiveToWrapper(elemClass);
    300        final Object array = Array.newInstance(elemClass, values.size());
    301        int idx = 0;
    302        for (final Object value : values) {
    303            Array.set(array, idx++, convertValue(ci.interpolate(value), targetClass, ci));
    304        }
    305        return array;
    306    }
    307
    308    /**
    309     * Helper method for converting all values of a source object and storing them in a collection.
    310     *
    311     * @param <T> the target type of the conversion
    312     * @param src the source object
    313     * @param elemClass the target class of the conversion
    314     * @param ci the {@code ConfigurationInterpolator}
    315     * @param dest the collection in which to store the results
    316     * @throws ConversionException if a conversion cannot be performed
    317     */
    318    private <T> void convertToCollection(final Object src, final Class<T> elemClass, final ConfigurationInterpolator ci, final Collection<T> dest) {
    319        for (final Object o : extractValues(ci.interpolate(src))) {
    320            dest.add(convert(o, elemClass, ci));
    321        }
    322    }
    323
    324    /**
    325     * Obtains a {@code ConfigurationInterpolator}. If the passed in one is not <b>null</b>, it is used. Otherwise, a
    326     * default one is returned.
    327     *
    328     * @param ci the {@code ConfigurationInterpolator} provided by the caller
    329     * @return the {@code ConfigurationInterpolator} to be used
    330     */
    331    private static ConfigurationInterpolator fetchInterpolator(final ConfigurationInterpolator ci) {
    332        return ci != null ? ci : NULL_INTERPOLATOR;
    333    }
    334}