The log parser plugin updates a job config with the following if the plugin is enabled for the job:

<parsingRulesPath>/apps/jenkins/master/parsing-rules/java-default.txt</parsingRulesPath>

Note the absolute path is used, even though the rules file is identified in the UI by its description, not its path.

The rules file description should be stored in the job configuration so that rules files can be moved around on disk without having to update all the job configs that use them.