Great questions.

- OSGi: offers run-time modularization (based on classloaders), with a more dynamic model (bundles can start/stop/load/unload). Often derided for its complexity, which Jigsaw has tried to reduce (in part by offering a less dynamic model)

- Forced modularization: fortunately, Java 9 has many migration features to allow incremental modularization. Most notable are automatic modules, which allow you to treat non-modularized JARs as modules, and interoperation between automatic modules and the classpath

Hope this helps.