Java EE microservices

As mentioned in The basic architecture of Java EE applications section, traditionally, in Java EE, you were creating JARs with your applications and deploying them on an application server. With microservices, we will like to transform the same kind of JARs into runnable services:

In a traditional scenario, the application server has to support all the APIs specified in the standard.

In a microservices scenario, we will like to transform each JAR, which is an implementation of a microservice, into a runnable JAR. This can be done by creating a runtime for the given microservice and assembling this runtime and the service's archive into a runnable JAR. Since the assembled runtime will be used by only one service, we don't have to include all the Java EE modules in it. The tool that builds your microservices will have to analyze your service's archive and create a runtime, which contains only those functionalities that are required by it.

We have already sketched how we can use Java EE as a base for microservices architecture, but what are the benefits that you will achieve by doing so? Firstly, you will be able to take advantage of proven technologies and your experience with them immediately. Moreover, there is a portability aspect. As we covered in the preceding section, you are encouraged to start with monolithic applications and refactor it microservices, if necessary. Owing to the common set of technologies used and the standard archive format that is used in both scenarios, you can easily migrate between the two, creating an elastic architecture that can be changed and refactored when necessary.