    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.Collections;
    022import java.util.Iterator;
    023import java.util.List;
    024
    025import org.apache.commons.lang3.StringUtils;
    026
    027/**
    028 * <p>
    029 * A specialized implementation of {@code ListDelimiterHandler} which simulates the list delimiter handling as it was
    030 * used by {@code PropertiesConfiguration} in Commons Configuration 1.x.
    031 * </p>
    032 * <p>
    033 * This class mainly exists for compatibility reasons. It is intended to be used by applications which have to deal with
    034 * properties files created by an older version of this library.
    035 * </p>
    036 * <p>
    037 * In the 1.x series of Commons Configuration list handling was not fully consistent. The escaping of property values
    038 * was done in a different way if they contained a list delimiter or not. From version 2.0 on, escaping is more
    039 * stringent which might cause slightly different results when parsing properties files created by or for Configuration
    040 * 1.x. If you encounter such problems, you can switch to this {@code ListDelimiterHandler} implementation rather than
    041 * the default one. In other cases, this class should not be used!
    042 * </p>
    043 * <p>
    044 * Implementation note: An instance of this class can safely be shared between multiple {@code Configuration} instances.
    045 * </p>
    046 *
    047 * @since 2.0
    048 */
    049public class LegacyListDelimiterHandler extends AbstractListDelimiterHandler {
    050    /** Constant for the escaping character. */
    051    private static final String ESCAPE = "\\";
    052
    053    /** Constant for the escaped escaping character. */
    054    private static final String DOUBLE_ESC = ESCAPE + ESCAPE;
    055
    056    /** Constant for a duplicated sequence of escaping characters. */
    057    private static final String QUAD_ESC = DOUBLE_ESC + DOUBLE_ESC;
    058
    059    /**
    060     * Returns the number of trailing backslashes. This is sometimes needed for the correct handling of escape characters.
    061     *
    062     * @param line the string to investigate
    063     * @return the number of trailing backslashes
    064     */
    065    private static int countTrailingBS(final String line) {
    066        int bsCount = 0;
    067        for (int idx = line.length() - 1; idx >= 0 && line.charAt(idx) == '\\'; idx--) {
    068            bsCount++;
    069        }
    070
    071        return bsCount;
    072    }
    073
    074    /** The list delimiter character. */
    075    private final char delimiter;
    076
    077    /**
    078     * Creates a new instance of {@code LegacyListDelimiterHandler} and sets the list delimiter character.
    079     *
    080     * @param listDelimiter the list delimiter character
    081     */
    082    public LegacyListDelimiterHandler(final char listDelimiter) {
    083        delimiter = listDelimiter;
    084    }
    085
    086    /**
    087     * {@inheritDoc} This implementation performs delimiter escaping for a single value (which is not part of a list).
    088     */
    089    @Override
    090    public Object escape(final Object value, final ValueTransformer transformer) {
    091        return escapeValue(value, false, transformer);
    092    }
    093
    094    /**
    095     * Performs the escaping of backslashes in the specified properties value. Because a double backslash is used to escape
    096     * the escape character of a list delimiter, double backslashes also have to be escaped if the property is part of a
    097     * (single line) list. In addition, because the output is written into a properties file, each occurrence of a backslash
    098     * again has to be doubled. This method is called by {@code escapeValue()}.
    099     *
    100     * @param value the value to be escaped
    101     * @param inList a flag whether the value is part of a list
    102     * @return the value with escaped backslashes as string
    103     */
    104    protected String escapeBackslashs(final Object value, final boolean inList) {
    105        String strValue = String.valueOf(value);
    106
    107        if (inList && strValue.contains(DOUBLE_ESC)) {
    108            strValue = StringUtils.replace(strValue, DOUBLE_ESC, QUAD_ESC);
    109        }
    110
    111        return strValue;
    112    }
    113
    114    /**
    115     * {@inheritDoc} This implementation performs a special encoding of backslashes at the end of a string so that they are
    116     * not interpreted as escape character for a following list delimiter.
    117     */
    118    @Override
    119    public Object escapeList(final List<?> values, final ValueTransformer transformer) {
    120        if (!values.isEmpty()) {
    121            final Iterator<?> it = values.iterator();
    122            String lastValue = escapeValue(it.next(), true, transformer);
    123            final StringBuilder buf = new StringBuilder(lastValue);
    124            while (it.hasNext()) {
    125                // if the last value ended with an escape character, it has
    126                // to be escaped itself; otherwise the list delimiter will
    127                // be escaped
    128                if (lastValue.endsWith(ESCAPE) && countTrailingBS(lastValue) / 2 % 2 != 0) {
    129                    buf.append(ESCAPE).append(ESCAPE);
    130                }
    131                buf.append(getDelimiter());
    132                lastValue = escapeValue(it.next(), true, transformer);
    133                buf.append(lastValue);
    134            }
    135            return buf.toString();
    136        }
    137        return null;
    138    }
    139
    140    /**
    141     * {@inheritDoc} This is just a dummy implementation. It is never called.
    142     */
    143    @Override
    144    protected String escapeString(final String s) {
    145        return null;
    146    }
    147
    148    /**
    149     * Escapes the given property value. This method is called on saving the configuration for each property value. It
    150     * ensures a correct handling of backslash characters and also takes care that list delimiter characters in the value
    151     * are escaped.
    152     *
    153     * @param value the property value
    154     * @param inList a flag whether the value is part of a list
    155     * @param transformer the {@code ValueTransformer}
    156     * @return the escaped property value
    157     */
    158    protected String escapeValue(final Object value, final boolean inList, final ValueTransformer transformer) {
    159        String escapedValue = String.valueOf(transformer.transformValue(escapeBackslashs(value, inList)));
    160        if (getDelimiter() != 0) {
    161            escapedValue = StringUtils.replace(escapedValue, String.valueOf(getDelimiter()), ESCAPE + getDelimiter());
    162        }
    163        return escapedValue;
    164    }
    165
    166    /**
    167     * Gets the list delimiter character.
    168     *
    169     * @return the list delimiter character
    170     */
    171    public char getDelimiter() {
    172        return delimiter;
    173    }
    174
    175    /**
    176     * {@inheritDoc} This implementation simulates the old splitting algorithm. The string is split at the delimiter
    177     * character if it is not escaped. If the delimiter character is not found, the input is returned unchanged.
    178     */
    179    @Override
    180    protected Collection<String> splitString(final String s, final boolean trim) {
    181        if (s.indexOf(getDelimiter()) < 0) {
    182            return Collections.singleton(s);
    183        }
    184
    185        final List<String> list = new ArrayList<>();
    186
    187        StringBuilder token = new StringBuilder();
    188        int begin = 0;
    189        boolean inEscape = false;
    190        final char esc = ESCAPE.charAt(0);
    191
    192        while (begin < s.length()) {
    193            final char c = s.charAt(begin);
    194            if (inEscape) {
    195                // last character was the escape marker
    196                // can current character be escaped?
    197                if (c != getDelimiter() && c != esc) {
    198                    // no, also add escape character
    199                    token.append(esc);
    200                }
    201                token.append(c);
    202                inEscape = false;
    203            } else if (c == getDelimiter()) {
    204                // found a list delimiter -> add token and
    205                // resetDefaultFileSystem buffer
    206                String t = token.toString();
    207                if (trim) {
    208                    t = t.trim();
    209                }
    210                list.add(t);
    211                token = new StringBuilder();
    212            } else if (c == esc) {
    213                // eventually escape next character
    214                inEscape = true;
    215            } else {
    216                token.append(c);
    217            }
    218
    219            begin++;
    220        }
    221
    222        // Trailing delimiter?
    223        if (inEscape) {
    224            token.append(esc);
    225        }
    226        // Add last token
    227        String t = token.toString();
    228        if (trim) {
    229            t = t.trim();
    230        }
    231        list.add(t);
    232
    233        return list;
    234    }
    235}