Spring Boot is an integration framework, which means that it does not implement various things itself, but provides an easy way to take a 3rd party implementation and plug it into your application. In Java there are multiple migration frameworks, including the ones that do migrations in a way similar to Rails. However, this approach is not very popular for exactly the same reasons people writing comments here distrust annotation-based configurations - it's not always obvious what an ORM will do for you. The recommended approach in Spring Boot is to use Flyway library which combines plain SQL migrations with custom Java code for complex data transformations and seeding the db.

Regarding ecosystem, the Java one is the biggest and has much more to offer than any other technology. Spring Boot can work with all libraries and there exist Spring Boot plugins for the configuration of the most popular solutions (data storages, clouds, templates, MQs etc).

The package management in Java is mature and one of the best and is now replicated/reused on other platforms. E.g. Java-based Nexus repository can be used for hosting libraries for JS and Docker and tools like Apache Maven can build and manage not only Java projects (I think it's even possible to wrap Rails project in Maven).