    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.ArrayList;
    021import java.util.Collection;
    022import java.util.Iterator;
    023import java.util.LinkedList;
    024
    025/**
    026 * <p>
    027 * An abstract base class for concrete {@code ListDelimiterHandler}
    028 * implementations.
    029 * </p>
    030 * <p>
    031 * This base class provides a fully functional implementation for parsing a
    032 * value object which can deal with different cases like collections, arrays,
    033 * iterators, etc. This logic is typically needed by every concrete subclass.
    034 * Other methods are partly implemented handling special corner cases like
    035 * <b>null</b> values; concrete subclasses do not have do implement the
    036 * corresponding checks.
    037 * </p>
    038 *
    039 * @since 2.0
    040 */
    041public abstract class AbstractListDelimiterHandler implements
    042        ListDelimiterHandler
    043{
    044    /**
    045     * {@inheritDoc} Depending on the type of the passed in object the following
    046     * things happen:
    047     * <ul>
    048     * <li>Strings are checked for delimiter characters and split if necessary.
    049     * This is done by calling the {@code split()} method.</li>
    050     * <li>For objects implementing the {@code Iterable} interface, the
    051     * corresponding {@code Iterator} is obtained, and contained elements are
    052     * added to the resulting iteration.</li>
    053     * <li>Arrays are treated as {@code Iterable} objects.</li>
    054     * <li>All other types are directly inserted.</li>
    055     * <li>Recursive combinations are supported, e.g. a collection containing an
    056     * array that contains strings: The resulting collection will only contain
    057     * primitive objects.</li>
    058     * </ul>
    059     */
    060    @Override
    061    public Iterable<?> parse(final Object value)
    062    {
    063        return flatten(value);
    064    }
    065
    066    /**
    067     * {@inheritDoc} This implementation handles the case that the passed in
    068     * string is <b>null</b>. In this case, an empty collection is returned.
    069     * Otherwise, this method delegates to {@link #splitString(String, boolean)}.
    070     */
    071    @Override
    072    public Collection<String> split(final String s, final boolean trim)
    073    {
    074        if (s == null)
    075        {
    076            return new ArrayList<>(0);
    077        }
    078        return splitString(s, trim);
    079    }
    080
    081    /**
    082     * {@inheritDoc} This implementation checks whether the object to be escaped
    083     * is a string. If yes, it delegates to {@link #escapeString(String)},
    084     * otherwise no escaping is performed. Eventually, the passed in transformer
    085     * is invoked so that additional encoding can be performed.
    086     */
    087    @Override
    088    public Object escape(final Object value, final ValueTransformer transformer)
    089    {
    090        final Object escValue =
    091                value instanceof String ? escapeString((String) value)
    092                        : value;
    093        return transformer.transformValue(escValue);
    094    }
    095
    096    /**
    097     * Actually splits the passed in string which is guaranteed to be not
    098     * <b>null</b>. This method is called by the base implementation of the
    099     * {@code split()} method. Here the actual splitting logic has to be
    100     * implemented.
    101     *
    102     * @param s the string to be split (not <b>null</b>)
    103     * @param trim a flag whether the single components have to be trimmed
    104     * @return a collection with the extracted components of the passed in
    105     *         string
    106     */
    107    protected abstract Collection<String> splitString(String s, boolean trim);
    108
    109    /**
    110     * Escapes the specified string. This method is called by {@code escape()}
    111     * if the passed in object is a string. Concrete subclasses have to
    112     * implement their specific escaping logic here, so that the list delimiters
    113     * they support are properly escaped.
    114     *
    115     * @param s the string to be escaped (not <b>null</b>)
    116     * @return the escaped string
    117     */
    118    protected abstract String escapeString(String s);
    119
    120    /**
    121     * Extracts all values contained in the specified object up to the given
    122     * limit. The passed in object is evaluated (if necessary in a recursive
    123     * way). If it is a complex object (e.g. a collection or an array), all its
    124     * elements are processed recursively and added to a target collection. The
    125     * process stops if the limit is reached, but depending on the input object,
    126     * it might be exceeded. (The limit is just an indicator to stop the process
    127     * to avoid unnecessary work if the caller is only interested in a few
    128     * values.)
    129     *
    130     * @param value the value to be processed
    131     * @param limit the limit for aborting the processing
    132     * @return a &quot;flat&quot; collection containing all primitive values of
    133     *         the passed in object
    134     */
    135    Collection<?> flatten(final Object value, final int limit)
    136    {
    137        if (value instanceof String)
    138        {
    139            return split((String) value, true);
    140        }
    141
    142        final Collection<Object> result = new LinkedList<>();
    143        if (value instanceof Iterable)
    144        {
    145            flattenIterator(result, ((Iterable<?>) value).iterator(), limit);
    146        }
    147        else if (value instanceof Iterator)
    148        {
    149            flattenIterator(result, (Iterator<?>) value, limit);
    150        }
    151        else if (value != null)
    152        {
    153            if (value.getClass().isArray())
    154            {
    155                for (int len = Array.getLength(value), idx = 0, size = 0; idx < len
    156                        && size < limit; idx++, size = result.size())
    157                {
    158                    result.addAll(flatten(Array.get(value, idx), limit - size));
    159                }
    160            }
    161            else
    162            {
    163                result.add(value);
    164            }
    165        }
    166
    167        return result;
    168    }
    169
    170    /**
    171     * Performs the actual work as advertised by the {@code parse()} method.
    172     * This method delegates to {@link #flatten(Object, int)} without specifying
    173     * a limit.
    174     *
    175     * @param value the value to be processed
    176     * @return a &quot;flat&quot; collection containing all primitive values of
    177     *         the passed in object
    178     */
    179    private Collection<?> flatten(final Object value)
    180    {
    181        return flatten(value, Integer.MAX_VALUE);
    182    }
    183
    184    /**
    185     * Flattens the given iterator. For each element in the iteration
    186     * {@code flatten()} is called recursively.
    187     *
    188     * @param target the target collection
    189     * @param it the iterator to process
    190     * @param limit a limit for the number of elements to extract
    191     */
    192    private void flattenIterator(final Collection<Object> target, final Iterator<?> it, final int limit)
    193    {
    194        int size = target.size();
    195        while (size < limit && it.hasNext())
    196        {
    197            target.addAll(flatten(it.next(), limit - size));
    198            size = target.size();
    199        }
    200    }
    201}