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.util.ArrayList;
020import java.util.Collection;
021import java.util.Iterator;
022
023/**
024 * <p>
025 * An abstract base class for concrete {@code ListDelimiterHandler} implementations.
026 * </p>
027 * <p>
028 * This base class provides a fully functional implementation for parsing a value object which can deal with different
029 * cases like collections, arrays, iterators, etc. This logic is typically needed by every concrete subclass. Other
030 * methods are partly implemented handling special corner cases like <b>null</b> values; concrete subclasses do not have
031 * do implement the corresponding checks.
032 * </p>
033 *
034 * @since 2.0
035 */
036public abstract class AbstractListDelimiterHandler implements ListDelimiterHandler {
037
038    /**
039     * Flattens the given iterator. For each element in the iteration {@code flatten()} is called recursively.
040     *
041     * @param handler the working handler
042     * @param target the target collection
043     * @param iterator the iterator to process
044     * @param limit a limit for the number of elements to extract
045     */
046    static void flattenIterator(final ListDelimiterHandler handler, final Collection<Object> target, final Iterator<?> iterator, final int limit) {
047        int size = target.size();
048        while (size < limit && iterator.hasNext()) {
049            target.addAll(handler.flatten(iterator.next(), limit - size));
050            size = target.size();
051        }
052    }
053
054    /**
055     * {@inheritDoc} This implementation checks whether the object to be escaped is a string. If yes, it delegates to
056     * {@link #escapeString(String)}, otherwise no escaping is performed. Eventually, the passed in transformer is invoked
057     * so that additional encoding can be performed.
058     */
059    @Override
060    public Object escape(final Object value, final ValueTransformer transformer) {
061        return transformer.transformValue(value instanceof String ? escapeString((String) value) : value);
062    }
063
064    /**
065     * Escapes the specified string. This method is called by {@code escape()} if the passed in object is a string. Concrete
066     * subclasses have to implement their specific escaping logic here, so that the list delimiters they support are
067     * properly escaped.
068     *
069     * @param s the string to be escaped (not <b>null</b>)
070     * @return the escaped string
071     */
072    protected abstract String escapeString(String s);
073
074    /**
075     * Performs the actual work as advertised by the {@code parse()} method. This method delegates to
076     * {@link #flatten(Object, int)} without specifying a limit.
077     *
078     * @param value the value to be processed
079     * @return a &quot;flat&quot; collection containing all primitive values of the passed in object
080     */
081    private Collection<?> flatten(final Object value) {
082        return flatten(value, Integer.MAX_VALUE);
083    }
084
085    /**
086     * {@inheritDoc} Depending on the type of the passed in object the following things happen:
087     * <ul>
088     * <li>Strings are checked for delimiter characters and split if necessary. This is done by calling the {@code split()}
089     * method.</li>
090     * <li>For objects implementing the {@code Iterable} interface, the corresponding {@code Iterator} is obtained, and
091     * contained elements are added to the resulting iteration.</li>
092     * <li>Arrays are treated as {@code Iterable} objects.</li>
093     * <li>All other types are directly inserted.</li>
094     * <li>Recursive combinations are supported, e.g. a collection containing an array that contains strings: The resulting
095     * collection will only contain primitive objects.</li>
096     * </ul>
097     */
098    @Override
099    public Iterable<?> parse(final Object value) {
100        return flatten(value);
101    }
102
103    /**
104     * {@inheritDoc} This implementation handles the case that the passed in string is <b>null</b>. In this case, an empty
105     * collection is returned. Otherwise, this method delegates to {@link #splitString(String, boolean)}.
106     */
107    @Override
108    public Collection<String> split(final String s, final boolean trim) {
109        return s == null ? new ArrayList<>(0) : splitString(s, trim);
110    }
111
112    /**
113     * Actually splits the passed in string which is guaranteed to be not <b>null</b>. This method is called by the base
114     * implementation of the {@code split()} method. Here the actual splitting logic has to be implemented.
115     *
116     * @param s the string to be split (not <b>null</b>)
117     * @param trim a flag whether the single components have to be trimmed
118     * @return a collection with the extracted components of the passed in string
119     */
120    protected abstract Collection<String> splitString(String s, boolean trim);
121}