Escaping special characters in Java Regular Expressions

Question

Is there any method in Java or any open source library for escaping  not quoting  a special character  meta-character   in order to use it as a regular expression   This would be very handy in dynamically building a regular expression  without having to manually escape each individual character   For example  consider a simple regex like  d    d  that matches numbers with a decimal point like 1 2  as well as the following code   String digit    d   String point        String regex1      d      d    String regex2   Pattern quote digit         point   digit          Pattern numbers1   Pattern compile regex1   Pattern numbers2   Pattern compile regex2    System out println  Regex 1      regex1    if  numbers1 matcher  1 2   matches          System out println   tMatch      else       System out println   tNo match       System out println  Regex 2      regex2    if  numbers2 matcher  1 2   matches          System out println   tMatch      else       System out println   tNo match        Not surprisingly  the output produced by the above code is   Regex 1   d    d      Match Regex 2   Qd  d  E     No match   That is  regex1 matches 1 2 but regex2  which is  dynamically  built  does not  instead  it matches the literal string d  d     So  is there a method that would automatically escape each regex meta-character   If there were  let s say  a static escape   method in java util regex Pattern  the output of  Pattern escape        would be the string       but   Pattern escape        should just produce      since it is not a meta-character  Similarly   Pattern escape  d     could produce   d   since  d  is used to denote digits  although escaping may not make sense in this case  as  d  could mean literal  d   which wouldn t be misunderstood by the regex interpeter to be something else  as would be the case with

User · Answer

Agree with Gray  as you may need your pattern to have both litrals          and meta-characters         so with some utility you should be able to escape all character first and then you can add meta-characters you want to add on same pattern

User · Answer

use  pattern compile        String s  p toString    yourcontent  p toString      will give result as yourcontent as is

User · Answer

The Pattern quote String s  sort of does what you want  However it leaves a little left to be desired  it doesn t actually escape the individual characters  just wraps the string with  Q    E    There is not a method that does exactly what you are looking for  but the good news is that it is actually fairly simple to escape all of the special characters in a Java regular expression   regex replaceAll     W          0     Why does this work  Well  the documentation for Pattern specifically says that its permissible to escape non-alphabetic characters that don t necessarily have to be escaped      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     For example    is not a special character in a regular expression  However  if you escape it  Pattern will still interpret    as    Here are a few more examples     gt  becomes   gt  which is equivalent to  gt    becomes    which is the escaped form of   8 is still 8     becomes      which is the escaped forms of   and   concatenated     Note  The key is is the definition of  non-alphabetic   which in the documentation really means  non-word  characters  or characters outside the character set  a-zA-Z 0-9

User · Answer

Use this Utility function escapeQuotes   in order to escape strings in between Groups and Sets of a RegualrExpression    List of Regex Literals to escape  lt      -            gt   public class RegexUtils       static String escapeChars                lt  gt   -           public static String escapeQuotes String str            if str    null  amp  amp  str length    gt  0                return str replaceAll     W          0        W designates non-word characters                   return               From the Pattern class the backslash character       serves to introduce escaped constructs  The string literal    hello    is illegal and leads to a compile-time error  in order to match the string  hello  the string literal     hello     must be used   Example  String to be matched  hello  and the regex with a group is    hello     Form here you only need to escape matched string as shown below  Test Regex online  public static void main String   args        String matched     hello    regexExpGrup         escapeQuotes matched             System out println  Regex      regexExpGrup         hello

User · Answer

I wrote this pattern   Pattern SPECIAL REGEX CHARS   Pattern compile                               And use it in this method   String escapeSpecialRegexChars String str         return SPECIAL REGEX CHARS matcher str  replaceAll       0        Then you can use it like this  for example   Pattern toSafePattern String text        return Pattern compile        escapeSpecialRegexChars text               We needed to do that because  after escaping  we add some regex expressions  If not  you can simply use  Q and  E   Pattern toSafePattern String text        return Pattern compile      Q    text      E

User · Answer

The only way the regex matcher knows you are looking for a digit and not the letter d is to escape the letter   d    To type the regex escape character in java  you need to escape it  so   becomes       So  there s no way around typing double backslashes for special regex chars

User · Answer

Is there any method in Java or any open source library for escaping  not quoting  a special character  meta-character   in order to use it as a regular expression    If you are looking for a way to create constants that you can use in your regex patterns  then just prepending them with      should work but there is no nice Pattern escape      function to help with this   So if you are trying to match    d   the string  d instead of a decimal character  then you would do      this will match on  d as opposed to a decimal character String matchBackslashD        d      as opposed to String matchDecimalDigit      d     The 4 slashes in the Java string turn into 2 slashes in the regex pattern   2 backslashes in a regex pattern matches the backslash itself   Prepending any special character with backslash turns it into a normal character instead of a special one   matchPeriod          matchPlus          matchParens                    In your post you use the Pattern quote string  method   This method wraps your pattern between    Q  and    E  so you can match a string even if it happens to have a special regex character in it          d  etc

[java] Escaping special characters in Java Regular Expressions

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