Difference between Pattern.quote
and Matcher.quoteReplacement
was not clear to me before I saw following example
s.replaceFirst(Pattern.quote("text to replace"),
Matcher.quoteReplacement("replacement text"));
Pattern.quote
replaces special characters in regex search strings, like .|+() etc, and Matcher.quoteReplacement
replaces special characters in replacement strings, like \1 for backreferences.
quoteReplacement
only cares about the two symbols $
and \
which can for example be used in replacement strings as backreferences $1
or \1
. It therefore must not be used to escape/quote a regex.
$Group$
with T$UYO$HI
. The $
symbol is special both in the pattern and in the replacement: "$Group$ Members".replaceFirst(Pattern.quote("$Group$"), Matcher.quoteReplacement("T$UYO$HI"))
It may be too late to respond, but you can also use Pattern.LITERAL
, which would ignore all special characters while formatting:
Pattern.compile(textToFormat, Pattern.LITERAL);
Pattern.CASE_INSENSITIVE
I think what you're after is \Q$5\E
. Also see Pattern.quote(s)
introduced in Java5.
See Pattern javadoc for details.
First off, if
you use replaceAll()
you DON'T use Matcher.quoteReplacement()
the text to be substituted in includes a $1
it won't put a 1 at the end. It will look at the search regex for the first matching group and sub THAT in. That's what $1, $2 or $3 means in the replacement text: matching groups from the search pattern.
I frequently plug long strings of text into .properties files, then generate email subjects and bodies from those. Indeed, this appears to be the default way to do i18n in Spring Framework. I put XML tags, as placeholders, into the strings and I use replaceAll() to replace the XML tags with the values at runtime.
I ran into an issue where a user input a dollars-and-cents figure, with a dollar sign. replaceAll() choked on it, with the following showing up in a stracktrace:
java.lang.IndexOutOfBoundsException: No group 3
at java.util.regex.Matcher.start(Matcher.java:374)
at java.util.regex.Matcher.appendReplacement(Matcher.java:748)
at java.util.regex.Matcher.replaceAll(Matcher.java:823)
at java.lang.String.replaceAll(String.java:2201)
In this case, the user had entered "$3" somewhere in their input and replaceAll() went looking in the search regex for the third matching group, didn't find one, and puked.
Given:
// "msg" is a string from a .properties file, containing "<userInput />" among other tags
// "userInput" is a String containing the user's input
replacing
msg = msg.replaceAll("<userInput \\/>", userInput);
with
msg = msg.replaceAll("<userInput \\/>", Matcher.quoteReplacement(userInput));
solved the problem. The user could put in any kind of characters, including dollar signs, without issue. It behaved exactly the way you would expect.
To have protected pattern you may replace all symbols with "\\\\", except digits and letters. And after that you can put in that protected pattern your special symbols to make this pattern working not like stupid quoted text, but really like a patten, but your own. Without user special symbols.
public class Test {
public static void main(String[] args) {
String str = "y z (111)";
String p1 = "x x (111)";
String p2 = ".* .* \\(111\\)";
p1 = escapeRE(p1);
p1 = p1.replace("x", ".*");
System.out.println( p1 + "-->" + str.matches(p1) );
//.*\ .*\ \(111\)-->true
System.out.println( p2 + "-->" + str.matches(p2) );
//.* .* \(111\)-->true
}
public static String escapeRE(String str) {
//Pattern escaper = Pattern.compile("([^a-zA-z0-9])");
//return escaper.matcher(str).replaceAll("\\\\$1");
return str.replaceAll("([^a-zA-Z0-9])", "\\\\$1");
}
}
Pattern.quote("blabla") works nicely.
The Pattern.quote() works nicely. It encloses the sentence with the characters "\Q" and "\E", and if it does escape "\Q" and "\E". However, if you need to do a real regular expression escaping(or custom escaping), you can use this code:
String someText = "Some/s/wText*/,**";
System.out.println(someText.replaceAll("[-\\[\\]{}()*+?.,\\\\\\\\^$|#\\\\s]", "\\\\$0"));
This method returns: Some/\s/wText*/\,**
Code for example and tests:
String someText = "Some\\E/s/wText*/,**";
System.out.println("Pattern.quote: "+ Pattern.quote(someText));
System.out.println("Full escape: "+someText.replaceAll("[-\\[\\]{}()*+?.,\\\\\\\\^$|#\\\\s]", "\\\\$0"));
^(Negation) symbol is used to match something that is not in the character group.
This is the link to Regular Expressions
Here is the image info about negation:
https://i.stack.imgur.com/m5cXU.png
Success story sharing
\Q
and\E
. This may lead to unexpected results, for examplePattern.quote("*.wav").replaceAll("*",".*")
will result in\Q.*.wav\E
and not.*\.wav
, as you might expect."mouse".toUpperCase().replaceAll("OUS","ic")
it will returnMicE
. You would’t expect it to returnMICE
because you didn’t applytoUpperCase()
onic
. In my examplequote()
is applied on the.*
insertet byreplaceAll()
as well. You have to do something else, perhaps.replaceAll("*","\\E.*\\Q")
would work, but that’s counterintuitive.*.wav
into the regex pattern\*\.wav
, and the replaceAll would turn it into\.*\.wav
, meaning it would match files whose name consists of a arbitrary number of periods followed by.wav
. You'd most likely have needed toreplaceAll("\\*", ".*")
if they'd gone with the more fragile implementation that relies on recognizing all possible active regex charachters and escaping them individually...would that be so much easier?"*.wav".replaceAll(Pattern.quote("*"), ".*")
.