Can java.util.regex.Pattern be used in a painless script?

[Jamshid]

Is there a way to use java.util.regex.Pattern in a painless script? I get an error:

curl -i -XPOST http://localhost:9200/_scripts/painless/_execute -H 'Content-type: application/json' --data-binary '{"script": {"source": "return java.util.regex.Pattern.matches(\"a*b\",\"aaab\");", "params": { "test":1 } } }'

HTTP/1.1 500 Internal Server Error
content-type: application/json; charset=UTF-8
content-length: 668

{"error":{"root_cause":[{"type":"script_exception","reason":"compile error","script_stack":["... n java.util.regex.Pattern.matches(\"a*b\",\"aaab\");","                             ^---- HERE"],"script":"return java.util.regex.Pattern.matches(\"a*b\",\"aaab\");","lang":"painless"}],"type":"script_exception","reason":"compile error","script_stack":["... n java.util.regex.Pattern.matches(\"a*b\",\"aaab\");","                             ^---- HERE"],"script":"return java.util.regex.Pattern.matches(\"a*b\",\"aaab\");","lang":"painless","caused_by":{"type":"illegal_argument_exception","reason":"method [java.util.regex.Pattern, matches/2] not found"}},"status":500}

Other java.util classes seem to work:

curl -i -XPOST http://localhost:9200/_scripts/painless/_execute -H 'Content-type: application/json' --data-binary '{"script": {"source": "new java.util.BitSet(10).length();", "params": { "test":1 } } }'

HTTP/1.1 200 OK
content-type: application/json; charset=UTF-8
content-length: 14

{"result":"0"}

I know there is built-in regex support but that requires the pattern be a literal, hard-coded string. A native script I'm trying to port to painless needs to use a regex pattern string passed as a parameter.

[spinscale (Alexander Reelsen)]

please see https://www.elastic.co/guide/en/elasticsearch/painless/7.5/painless-walkthrough.html#modules-scripting-painless-regex - especially about enabling regexes and how regexes are used. Pattern.compile is not included intentionally.