Java ^正则表达式与字符串中的新行不匹配

Question

this is my String

REGISTER sip:192.168.178.1 SIP/2.0
Call-ID: bla@192.168.178.60
CSeq: 1441 REGISTER
From: "620" <sip:620@192.168.178.20>;tag=bla
To: "620" <sip:620@192.168.178.20>
Via: SIP/2.0UDP 192.168.178.60:59488;branch=bla;rport
Max-Forwards: 70
User-Agent: bla
Contact: *
Expires: 0
Content-Length: 0

So this string has several newlines. My Regex is in this form:

sipRequest = sipRequest.replaceFirst("(From: \")(.*)(\" <sip:)(.*)@(.*)>", "$1$2$3$4@" + sipServer + ">");

This Regex matches, but not the following one:

sipRequest = sipRequest.replaceFirst("(^From: \")(.*)(\" <sip:)(.*)@(.*)>", "$1$2$3$4@" + sipServer + ">");

Note: Only difference is the "^" sign before "From". So why does this expression not match? It starts at a new line, so it should match.

Thanks for help.

Answer 1

Quoting the JavaDoc of Pattern :

By default, the regular expressions ^ and $ ignore line terminators and only match at the beginning and the end, respectively, of the entire input sequence. If MULTILINE mode is activated then ^ matches at the beginning of input and after any line terminator except at the end of input. When in MULTILINE mode $ matches just before a line terminator or the end of the input sequence.

So you need to set the multiline flag, because the default meaning of ^ is beginning of string , not beginning of line.

Answer 2

The operation ^ works only if you are using Pattern.MULTILINE . Since string.replaceAll() creates patterns without options you have to create pattern yourself, than create matcher and use replacing facilities of matcher.