    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.Collection;
    020import java.util.LinkedList;
    021import java.util.List;
    022
    023import org.apache.commons.lang3.StringUtils;
    024
    025/**
    026 * <p>
    027 * The default implementation of the {@code ListDelimiterHandler} interface.
    028 * </p>
    029 * <p>
    030 * This class supports list splitting and delimiter escaping using a delimiter
    031 * character that can be specified when constructing an instance. Splitting of
    032 * strings works by scanning the input for the list delimiter character. The
    033 * list delimiter character can be escaped by a backslash. So, provided that a
    034 * comma is configured as list delimiter, in the example {@code val1,val2,val3}
    035 * three values are recognized. In {@code 3\,1415} the list delimiter is escaped
    036 * so that only a single element is detected. (Note that when writing these
    037 * examples in Java code, each backslash has to be doubled. This is also true
    038 * for all other examples in this documentation.)
    039 * </p>
    040 * <p>
    041 * Because the backslash has a special meaning as escaping character it is
    042 * always treated in a special way. If it occurs as a normal character in a
    043 * property value, it has to be escaped using another backslash (similar to the
    044 * rules of the Java programming language). The following example shows the
    045 * correct way to define windows network shares: {@code \\\\Server\\path}. Note
    046 * that each backslash is doubled. When combining the list delimiter with
    047 * backslashes the same escaping rules apply. For instance, in
    048 * {@code C:\\Temp\\,D:\\data\\} the list delimiter is recognized; it is not
    049 * escaped by the preceding backslash because this backslash is itself escaped.
    050 * In contrast, {@code C:\\Temp\\\,D:\\data\\} defines a single element with a
    051 * comma being part of the value; two backslashes after {@code Temp} result in a
    052 * single one, the third backslash escapes the list delimiter.
    053 * </p>
    054 * <p>
    055 * As can be seen, there are some constellations which are a bit tricky and
    056 * cause a larger number of backslashes in sequence. Nevertheless, the escaping
    057 * rules are consistent and do not cause ambiguous results.
    058 * </p>
    059 * <p>
    060 * Implementation node: An instance of this class can safely be shared between
    061 * multiple {@code Configuration} instances.
    062 * </p>
    063 *
    064 * @since 2.0
    065 */
    066public class DefaultListDelimiterHandler extends AbstractListDelimiterHandler
    067{
    068    /** Constant for the escape character. */
    069    private static final char ESCAPE = '\\';
    070
    071    /**
    072     * Constant for a buffer size for escaping strings. When a character is
    073     * escaped the string becomes longer. Therefore, the output buffer is longer
    074     * than the original string length. But we assume, that there are not too
    075     * many characters that need to be escaped.
    076     */
    077    private static final int BUF_SIZE = 16;
    078
    079    /** Stores the list delimiter character. */
    080    private final char delimiter;
    081
    082    /**
    083     * Creates a new instance of {@code DefaultListDelimiterHandler} and sets
    084     * the list delimiter character.
    085     *
    086     * @param listDelimiter the list delimiter character
    087     */
    088    public DefaultListDelimiterHandler(final char listDelimiter)
    089    {
    090        delimiter = listDelimiter;
    091    }
    092
    093    /**
    094     * Returns the list delimiter character used by this instance.
    095     *
    096     * @return the list delimiter character
    097     */
    098    public char getDelimiter()
    099    {
    100        return delimiter;
    101    }
    102
    103    @Override
    104    public Object escapeList(final List<?> values, final ValueTransformer transformer)
    105    {
    106        final Object[] escapedValues = new String[values.size()];
    107        int idx = 0;
    108        for (final Object v : values)
    109        {
    110            escapedValues[idx++] = escape(v, transformer);
    111        }
    112        return StringUtils.join(escapedValues, getDelimiter());
    113    }
    114
    115    @Override
    116    protected String escapeString(final String s)
    117    {
    118        final StringBuilder buf = new StringBuilder(s.length() + BUF_SIZE);
    119        for (int i = 0; i < s.length(); i++)
    120        {
    121            final char c = s.charAt(i);
    122            if (c == getDelimiter() || c == ESCAPE)
    123            {
    124                buf.append(ESCAPE);
    125            }
    126            buf.append(c);
    127        }
    128        return buf.toString();
    129    }
    130
    131    /**
    132     * {@inheritDoc} This implementation reverses the escaping done by the
    133     * {@code escape()} methods of this class. However, it tries to be tolerant
    134     * with unexpected escaping sequences: If after the escape character "\" no
    135     * allowed character follows, both the backslash and the following character
    136     * are output.
    137     */
    138    @Override
    139    protected Collection<String> splitString(final String s, final boolean trim)
    140    {
    141        final List<String> list = new LinkedList<>();
    142        StringBuilder token = new StringBuilder();
    143        boolean inEscape = false;
    144
    145        for (int i = 0; i < s.length(); i++)
    146        {
    147            final char c = s.charAt(i);
    148            if (inEscape)
    149            {
    150                // last character was the escape marker
    151                // can current character be escaped?
    152                if (c != getDelimiter() && c != ESCAPE)
    153                {
    154                    // no, also add escape character
    155                    token.append(ESCAPE);
    156                }
    157                token.append(c);
    158                inEscape = false;
    159            }
    160
    161            else
    162            {
    163                if (c == getDelimiter())
    164                {
    165                    // found a list delimiter -> add token and
    166                    // reset buffer
    167                    String t = token.toString();
    168                    if (trim)
    169                    {
    170                        t = t.trim();
    171                    }
    172                    list.add(t);
    173                    token = new StringBuilder();
    174                }
    175                else if (c == ESCAPE)
    176                {
    177                    // potentially escape next character
    178                    inEscape = true;
    179                }
    180                else
    181                {
    182                    token.append(c);
    183                }
    184            }
    185        }
    186
    187        // Trailing delimiter?
    188        if (inEscape)
    189        {
    190            token.append(ESCAPE);
    191        }
    192        // Add last token
    193        String t = token.toString();
    194        if (trim)
    195        {
    196            t = t.trim();
    197        }
    198        list.add(t);
    199
    200        return list;
    201    }
    202}