Escapes characters that have special meaning to regular expressions
/*
* Static String formatting and query routines.
* Copyright (C) 2001-2005 Stephen Ostermiller
* http://ostermiller.org/contact.pl?regarding=Java+Utilities
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* See COPYING.TXT for details.
*/
import java.util.HashMap;
import java.util.regex.Pattern;
/**
* Utilities for String formatting, manipulation, and queries.
* More information about this class is available from <a target="_top" href=
* "http://ostermiller.org/utils/StringHelper.html">ostermiller.org</a>.
*
* @author Stephen Ostermiller http://ostermiller.org/contact.pl?regarding=Java+Utilities
* @since ostermillerutils 1.00.00
*/
public class StringHelper {
/**
* Escapes characters that have special meaning to
* regular expressions
*
* @param s String to be escaped
* @return escaped String
* @throws NullPointerException if s is null.
*
* @since ostermillerutils 1.02.25
*/
public static String escapeRegularExpressionLiteral(String s){
// According to the documentation in the Pattern class:
//
// The backslash character ('\') serves to introduce escaped constructs,
// as defined in the table above, as well as to quote characters that
// otherwise would be interpreted as unescaped constructs. Thus the
// expression \\ matches a single backslash and \{ matches a left brace.
//
// It is an error to use a backslash prior to any alphabetic character
// that does not denote an escaped construct; these are reserved for future
// extensions to the regular-expression language. A backslash may be used
// prior to a non-alphabetic character regardless of whether that character
// is part of an unescaped construct.
//
// As a result, escape everything except [0-9a-zA-Z]
int length = s.length();
int newLength = length;
// first check for characters that might
// be dangerous and calculate a length
// of the string that has escapes.
for (int i=0; i<length; i++){
char c = s.charAt(i);
if (!((c>='0' && c<='9') || (c>='A' && c<='Z') || (c>='a' && c<='z'))){
newLength += 1;
}
}
if (length == newLength){
// nothing to escape in the string
return s;
}
StringBuffer sb = new StringBuffer(newLength);
for (int i=0; i<length; i++){
char c = s.charAt(i);
if (!((c>='0' && c<='9') || (c>='A' && c<='Z') || (c>='a' && c<='z'))){
sb.append('\\');
}
sb.append(c);
}
return sb.toString();
}
}
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