REST API Java microservice available inside same application server

Question

I have small Java (Java EE) microservice, that do some calculations. This microservice is running on the same application server as other application, also written in Java EE. First question - should these apps communicate each other by REST API or different way? Second question - if so, is there a way to save some time, by not serializing/deserializing transfer objects? I understand that communication between two apps on different servers (languages) requires serialization/deserialization, but what about mentioned situation?

Answer 1

should these apps communicate each other by REST API or different way?

Microservices should communicate over network always. If they have a REST API then use that.

if so, is there a way to save some time, by not serializing/ deserializing transfer objects?

If they are communicating over network the serialization is a must. Anyway, serialization help the decoupling. Microservices should share data but not schema/classes. The serialization must be done by loosing the schema, i.e. you could use JSON. If you share the schema (classes) you break the microservice's encapsulation. You won't be able to change a microservice implementation with other implementation (that is using a different technology stack, PHP with Nginx for example).