Java Pattern regex search between strings

Question

Given the following strings (stringToTest):

1. G2:7JAPjGdnGy8jxR8[RQ:1,2]-G3:jRo6pN8ZW9aglYz[RQ:3,4]
2. G2:7JAPjGdnGy8jxR8[RQ:3,4]-G3:jRo6pN8ZW9aglYz[RQ:3,4]

And the Pattern:

Pattern p = Pattern.compile("G2:\\S+RQ:3,4");
if (p.matcher(stringToTest).find())
{
    // Match
}

For string 1 I DON'T want to match, because RQ:3,4 is associated with the G3 section, not G2, and I want string 2 to match, as RQ:3,4 is associated with G2 section.

The problem with the current regex is that it's searching too far and reaching the RQ:3,4 eventually in case 1 even though I don't want to consider past the G2 section.

It's also possible that the stringToTest might be (just one section):

G2:7JAPjGdnGy8jxR8[RQ:3,4]

The strings 7JAPjGdnGy8jxR8 and jRo6pN8ZW9aglYz are variable length hashes.

Can anyone help me with the correct regex to use, to start looking at G2 for RQ:3,4 but stopping if it reaches the end of the string or -G (the start of the next section).

Answer 1

You may use this regex with a negative lookahead in between:

G2:(?:(?!G\d+:)\S)*RQ:3,4

RegEx Demo

RegEx Details:

• G2:: Match literal text G2:
• (?: Start a non-capture group
  • (?!G\d+:): Assert that we don't have a G<digit>: ahead of us
  • \S: Match a non-whitespace character
• )*: End non-capture group. Match 0 or more of this
• RQ:3,4: Match literal text RQ:3,4

In Java use this regex:

String re = "G2:(?:(?!G\\d+:)\\S)*RQ:3,4";