replacing regex in java string, which contains `
` symbol

Question

I have to replace the content of this xml string through java

<My:tag>value_1 22&#xA;value_2 54&#xA;value_3 11</My:tag>

so, this string has been taken from an xml and when I acquire it I have this result:

<My:tag>value_1 22
value_2 54
value_3 11</My:tag>

If I try to replace the content by this way:

String regex =  "(<My:tag>)(.*)(</My:tag>)";
String new_string = old_string.replaceAll(regex,"<My:tag> new_stuff </My:tag>");

I get no result. I think because of the 
 symbol

but if I try to replace the string without the 
 symbol, everything goes fine.

Suggestions? Thanks

Answer 1

I'd suggest using an XML library like JDOM or DOM4J for manipulating XML instead of using regular expressions.

Answer 2

I'm not 100% sure how the java regex-engine works, but I can't possibly imagine that an entity would cause your problems. You should first try to simply remove your brackets, since you're replacing the entire expression, and not extracting anything.

What might be causing it though is if your entity is actually translated to a new-line, it might be the case that your regex won't catch it unless you're explicitly doing a multiline match. You could also try doing

[.\n]*

instead of your

.*

This might be a bid greedy though, and the backtracking to much for the matcher to handle. Unfortunately, I don't have any java stuff installed on this machine, so I can't really try it and test it. One other possibility would be to actively look for the next opening angle bracket, like so:

[^<]*

EDIT:
As you suggested, i tried your link and the following worked perfectly:

Expression:

<My:tag>[^<]*</My:tag>

Replacement:

<My:tag> new_stuff </My:tag>

Test string:

<My:tag>value_1 22&#xA;value_2 54&#xA;value_3 11</My:tag>

Answer 3

I can't see why the 
 itself would cause any issue - not unless it's getting converted to an actual newline at some point.

If this is the case, you need to enable DOTALL mode, so that the . matches newline also (which it doesn't by default).

To enable DOTALL, simply start the expression with (?s)
(if you created a Pattern object, you could also pass the flag in to that.)

Anyway, try this:

String regex =  "(?s)(?<=<(My:tag)>).*?(?=</\1>)";
String new_string = old_string.replaceAll(regex,"new_stuff");

You can also enable it for a specific part of a regex with (?s:regex-segment) for example:

String regex =  "(?<=<(My:tag)>)(?s:.*?)(?=</\1>)";