Good kata, but need to add some tests like a -3., 50. etc.
My solution was applied, but returns true with examples above. Good luck further

Does it necessary paste "+" after first character class?

Hah, sorry, that's my bad. I didn't see that number included in [...]. Sorry again

Does Java have that flag? I had tried find this, but only see it with JavaScript.

My non-perfomance code crashes perfomance test and allow me to "Final Submit" when I just try to print str1 and str2 params

There are nice to replace your (\w\w\w*) to (\w{2,}) (means "2 letters and more")
But with your solution I got nice knowleadge about group()!

There are should be string.replaceFirst instead of string.replace

It's amazing kata. I need to solve this

My bad with isPalindrome. Should be likes:
if (numInString.equals(new StringBuilder(numInString).reverse().toString()))
return true;

You are awesome.....