Java正则表达式替换所有多行

Question

I have a problem with the replaceAll for a multiline string:

String regex = "\\s*/\\*.*\\*/";
String testWorks = " /** this should be replaced **/ just text";
String testIllegal = " /** this should be replaced \n **/ just text";

testWorks.replaceAll(regex, "x"); 
testIllegal.replaceAll(regex, "x"); 

The above works for testWorks, but not for testIllegal!? Why is that and how can I overcome this? I need to replace something like a comment /* ... */ that spans multiple lines.

Answer 1

You need to use the Pattern.DOTALL flag to say that the dot should match newlines. eg

Pattern.compile(regex, Pattern.DOTALL).matcher(testIllegal).replaceAll("x")

or alternatively specify the flag in the pattern using (?s) eg

String regex = "(?s)\\s*/\\*.*\\*/";

Answer 2

Add Pattern.DOTALL to the compile, or (?s) to the pattern.

This would work

String regex = "(?s)\\s*/\\*.*\\*/";

See Match multiline text using regular expression

Answer 3

The meta character . matches any character other than newline. That is why your regex does not work for multi line case.

To fix this replace . with [\\d\\D] that matches any character including newline.

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