Added test case for api : _api/web/doesuserhavepermissions, you can use this example to test for a specific permission of a specific user. You must add the user to the SharePoint owner group, otherwise it will return false. If the user don’t event have right to enter the subsite, the api will return 403.

https://gitlab.com/quantr/sharepoint/Sharepoint-Java-API/blob/83750c61ec040a699ca02525bc4402ad7ae69227/src/test/java/hk/quantr/sharepoint/TestHavePermissions.java

The library is open source https://gitlab.com/quantr/sharepoint/Sharepoint-Java-API