Regex nested backreference

Question

Is it possible to get a nested back reference to the below regex:

<field(.*)name="(.*)EndTime"(.*)\n((.*)\n)*?<property name="fieldClass" value="java.lang.String"/>\n</field>

Ie the "((.*)\n)*?"

Answer 1

Yes, this is quite possible. Just be certain to watch for which numbered group you're using. Capturing groups (and thus backreferences) are numbered according to which opening bracket comes first - so, in this case, the outer brackets would yield \1, and the inner ones would yield \2.

For example, the pattern ((.+)ab)\1\2 will match the string 1234ab1234ab1234. The first capture group will match the 4 numbers plus the ab, while the second (inner) capture group will only match the numbers. Then we repeat each one, yielding the full match.