WorkLogPRO REST API is available on Apiary. You can browse our API and generate source code for various programming languages. It has a lot of options when compared to only textual api documentation. We strongly suggest you to give it a try.
WorklogPRO Java API is available here. You can use Java API for integration with your own apps, Script Runner scripts or "Worklog Verification" scripts.
WorklogPRO also has build-in scripting feature which allows you to verify worklogs, do custom actions when work logged, timesheet approved etc. Please check Scripting page for more details.