Escapes characters that have special meaning to regular expressions - Java java.lang

Java examples for java.lang:String Escape

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Description

Escapes characters that have special meaning to regular expressions

Demo Code

/*/*from   w  w w  .j  a  v a2  s. co  m*/
 * 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.
 */
//package com.java2s;

public class Main {
    public static void main(String[] argv) {
        String s = "java2s.com";
        System.out.println(escapeRegularExpressionLiteral(s));
    }

    /**
     * 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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