If you are on the java platform I have an unpopular recommendation: get familiar with OSGi. Its specs, its history and its core concepts. The learning path you

If you are on the java platform I have an unpopular recommendation: get familiar with OSGi. Its specs, its history and its core concepts. The learning path you go will teach you a lot about how to build systems, how to think about api design, modularisation and standards (compared to one-off company owned tech). Its almost certainly makes you a better developer/thinker.