Adding answer for IntelliJ Idea 2022 UE.
Embedded persisted derby DB is created in your project directory, there should be derby.log file and db directory (after the app was launched at least once). May also check the derby.log text file whether the db was created successfully.
- Stop application (embedded db has to be accessed by one app at at time)
- From IntelliJ menu select: View->Tools->Database
- On a newly opened Database panel select New->Datasource from path->Provide path to embedded directory. Also, select Driver: Apache Embedded.
- On Data Source and Drivers Dialog select Authentication: No auth and click OK. On the same dialog switch to 'Schemas' tab and select 'All schemas'. Click OK.
- Now the DB would be present in a pane, unfold it and unfold the SA Scheme.
There it contains your tables.
Press 'deactivate' on the pane to disconnect the DB viewer prior to relaunching the application.