String replaceAll single backslashes with double backslashes

Question

I m trying to convert the String   something  into the String   something   using replaceAll  but I keep getting all kinds of errors  I thought this was the solution   theString replaceAll                  But this gives the below exception    java util regex PatternSyntaxException  Unexpected internal error near index 1

User · Answer

TLDR  use theString   theString replace                instead     Problem  replaceAll target  replacement  uses regular expression  regex  syntax for target and partially for replacement     Problem is that   is special character in regex  it can be used like  d to represents digit  and in String literal  it can be used like   n  to represent line separator or    to escape double quote symbol which normally would represent end of string literal      In both these cases to create   symbol we can escape it  make it literal instead of special character  by placing additional   before it  like we escape   in string literals via        So to target regex representing   symbol will need to hold     and string literal representing such text will need to look like           So we escaped   twice    once in regex    once in String literal         each   is represented as           In case of replacement   is also special there  It allows us to escape other special character   which via  x notation  allows us to use portion of data matched by regex and held by capturing group indexed as x  like  012  replaceAll     d      1 1   will match each digit  place it in capturing group 1 and  1 1 will replace it with its two copies  it will duplicate it  resulting in  001122    So again  to let replacement represent   literal we need to escape it with additional   which means that    replacement must hold two backslash characters    and String literal which represents    looks like          BUT since we want replacement to hold two backslashes we will need             each   represented by one           So version with replaceAll can look like  replaceAll                        Easier way  To make out life easier Java provides tools to automatically escape text into target and replacement parts  So now we can focus only on strings  and forget about regex syntax   replaceAll Pattern quote target   Matcher quoteReplacement replacement     which in our case can look like  replaceAll Pattern quote        Matcher quoteReplacement            Even better  If we don t really need regex syntax support lets not involve replaceAll at all  Instead lets use replace  Both methods will replace all targets  but replace doesn t involve regex syntax  So you could simply write   theString   theString replace

User · Answer

The String replaceAll   interprets the argument as a regular expression  The   is an escape character in both String and regex  You need to double-escape it for regex   string replaceAll                        But you don t necessarily need regex for this  simply because you want an exact character-by-character replacement and you don t need patterns here  So String replace   should suffice   string replace                    Update  as per the comments  you appear to want to use the string in JavaScript context  You d perhaps better use StringEscapeUtils escapeEcmaScript   instead to cover more characters

User · Answer

To avoid this sort of trouble  you can use replace  which takes a plain string  instead of replaceAll  which takes a regular expression   You will still need to escape backslashes  but not in the wild ways required with regular expressions

User · Answer

Yes    by the time the regex compiler sees the pattern you ve given it  it sees only a single backslash  since Java s lexer has turned the double backwhack into a single one   You need to replace        with         believe it or not  Java really needs a good raw string syntax

User · Answer

You ll need to escape the  escaped  backslash in the first argument as it is a regular expression  Replacement  2nd argument - see Matcher replaceAll String   also has it s special meaning of backslashes  so you ll have to replace those to   theString replaceAll

[java] String.replaceAll single backslashes with double backslashes

Problem

Easier way

Even better

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