Might be worth considering https://roadmap.sh/java/projects Check for advanced ones More on reddit.com

Here's a Spring project for a cancer research application that a lot of researchers use: https://github.com/cBioPortal/cbioportal/issues They're good people and they do important work; you may be able to find an issue or two you can make a PR for. More on reddit.com

An easy way would be to take a site that you use and create a clone. If that's too straightforward then you could take that site and try to put your own improvements to it. For example, make a reddit clone. If there's something you don't like that you could change, or something new and interesting that you could add then that could be a good project idea. More on reddit.com

Just find an API you want information from and build around it. For instance, find an open API showing updated flight times for air traffic. Then do the following: Find some information from the API, e.g. the next flight arriving at your nearest airport Create a simple website to display your data Deploy it Now you have a project you can continually add to when you want to develop or show off a new skill. For instance: Write your infrastructure as code e.g. with Terraform, Serverless Build a CI/CD pipeline Add login functionality Integrate a database, e.g. for storing location data Add service workers and a manifest so it can be used as a PWA Rewrite the whole thing using a different library/framework/language to compare functionality etc. You don't need to have one big idea and make the whole thing. Start with a tiny, simple, pointless idea, make that in the easiest way you can, then build on it. More on reddit.com