There is nothing new in writing Micro-services. If you can create a web-app in Java you can write micro-services too.
Micro-service is a architectural pattern which defines how the system architecture will work, not the way its programmed.
If you have a larger web-app and you have decomposed it into smaller individual unit that can work independently congrats, you have the new micro-services.
PS: With moving to micro-services architecture, number of new challenges will come like routing, gateway, discovery , security ..etc.
For Java, Spring Boot is the best suitable option to go with micro-services.