DefaultListDelimiterHandler.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2.convert;
import java.util.Collection;
import java.util.LinkedList;
import java.util.List;
import org.apache.commons.lang3.StringUtils;
/**
* <p>
* The default implementation of the {@code ListDelimiterHandler} interface.
* </p>
* <p>
* This class supports list splitting and delimiter escaping using a delimiter character that can be specified when
* constructing an instance. Splitting of strings works by scanning the input for the list delimiter character. The list
* delimiter character can be escaped by a backslash. So, provided that a comma is configured as list delimiter, in the
* example {@code val1,val2,val3} three values are recognized. In {@code 3\,1415} the list delimiter is escaped so that
* only a single element is detected. (Note that when writing these examples in Java code, each backslash has to be
* doubled. This is also true for all other examples in this documentation.)
* </p>
* <p>
* Because the backslash has a special meaning as escaping character it is always treated in a special way. If it occurs
* as a normal character in a property value, it has to be escaped using another backslash (similar to the rules of the
* Java programming language). The following example shows the correct way to define windows network shares:
* {@code \\\\Server\\path}. Note that each backslash is doubled. When combining the list delimiter with backslashes the
* same escaping rules apply. For instance, in {@code C:\\Temp\\,D:\\data\\} the list delimiter is recognized; it is not
* escaped by the preceding backslash because this backslash is itself escaped. In contrast,
* {@code C:\\Temp\\\,D:\\data\\} defines a single element with a comma being part of the value; two backslashes after
* {@code Temp} result in a single one, the third backslash escapes the list delimiter.
* </p>
* <p>
* As can be seen, there are some constellations which are a bit tricky and cause a larger number of backslashes in
* sequence. Nevertheless, the escaping rules are consistent and do not cause ambiguous results.
* </p>
* <p>
* Implementation node: An instance of this class can safely be shared between multiple {@code Configuration} instances.
* </p>
*
* @since 2.0
*/
public class DefaultListDelimiterHandler extends AbstractListDelimiterHandler {
/** Constant for the escape character. */
private static final char ESCAPE = '\\';
/**
* Constant for a buffer size for escaping strings. When a character is escaped the string becomes longer. Therefore,
* the output buffer is longer than the original string length. But we assume, that there are not too many characters
* that need to be escaped.
*/
private static final int BUF_SIZE = 16;
/** Stores the list delimiter character. */
private final char delimiter;
/**
* Creates a new instance of {@code DefaultListDelimiterHandler} and sets the list delimiter character.
*
* @param listDelimiter the list delimiter character
*/
public DefaultListDelimiterHandler(final char listDelimiter) {
delimiter = listDelimiter;
}
@Override
public Object escapeList(final List<?> values, final ValueTransformer transformer) {
final Object[] escapedValues = new Object[values.size()];
int idx = 0;
for (final Object v : values) {
escapedValues[idx++] = escape(v, transformer);
}
return StringUtils.join(escapedValues, getDelimiter());
}
@Override
protected String escapeString(final String s) {
final StringBuilder buf = new StringBuilder(s.length() + BUF_SIZE);
for (int i = 0; i < s.length(); i++) {
final char c = s.charAt(i);
if (c == getDelimiter() || c == ESCAPE) {
buf.append(ESCAPE);
}
buf.append(c);
}
return buf.toString();
}
/**
* Gets the list delimiter character used by this instance.
*
* @return the list delimiter character
*/
public char getDelimiter() {
return delimiter;
}
/**
* {@inheritDoc} This implementation reverses the escaping done by the {@code escape()} methods of this class. However,
* it tries to be tolerant with unexpected escaping sequences: If after the escape character "\" no allowed character
* follows, both the backslash and the following character are output.
*/
@Override
protected Collection<String> splitString(final String s, final boolean trim) {
final List<String> list = new LinkedList<>();
StringBuilder token = new StringBuilder();
boolean inEscape = false;
for (int i = 0; i < s.length(); i++) {
final char c = s.charAt(i);
if (inEscape) {
// last character was the escape marker
// can current character be escaped?
if (c != getDelimiter() && c != ESCAPE) {
// no, also add escape character
token.append(ESCAPE);
}
token.append(c);
inEscape = false;
} else if (c == getDelimiter()) {
// found a list delimiter -> add token and
// reset buffer
String t = token.toString();
if (trim) {
t = t.trim();
}
list.add(t);
token = new StringBuilder();
} else if (c == ESCAPE) {
// potentially escape next character
inEscape = true;
} else {
token.append(c);
}
}
// Trailing delimiter?
if (inEscape) {
token.append(ESCAPE);
}
// Add last token
String t = token.toString();
if (trim) {
t = t.trim();
}
list.add(t);
return list;
}
}