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