Well, this is the question, why? And the short answer is simple: because Java EE 8 is the most lightweight enterprise framework currently out there. Let me give you a few more details. First up, Java EE is an industry standard. It's been developed by a vendor-neutral committee and there is widespread knowledge out there because Java EE has been available for a couple of years already. Java EE consists of several specifications, and these specifications have very tight integration. Also, Java EE applies a convention of a configuration programming model, which means that you don't need cumbersome XML descriptors anymore; just throw in a couple of annotations and you're done. For most of the services you're going to develop, you will not need any external dependencies, and this leads to thin deployment artifacts. And finally, you have the availability of modern application servers that suit the cloud era.
Why is Java EE a good platform for microservices?
Java EE version history
If you have a look at the Java EE version history, which you can find at https://en.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition, you'll see we've come a long way since J2EE 1.2 was first released on December 12, 1999. If you look on the far-right side in the following diagram, you can see Java EE 8 was released on September 21, 2017, which means we have 18 years of experience and 18 years of community-built knowledge. Therefore it's definitely a very mature and stable API that's been continually improved:
Overview of Java EE 8
In the following diagram, you can see an overview of Java EE 8 in its current state, you have loads of APIs here that you can program against, and it should meet most of the needs of any enterprise's web-service development. You've got JPA for persistence, JMS for messaging, good JAX-WS for web services in structure, JAX-RS for REST services, and many more APIs you can use for your modern enterprise's application development:
And all you need is the following code, which is the only dependency required; this is the Maven dependency for the Java EE 8 API and leads to no external dependencies. All you need is Java EE 8 and Java 8; this results in very thin artifacts which speeds up your daily development and your deployment cycles, and because you have those thin WAR files, this is very Docker-friendly:
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-api</artifactId>
<version>8.0</version>
<scope>provided</scope>
</dependency>
Now there are people out there who say that Java EE 8, especially the application service, should not go in a Docker container, but those heavy times are over; modern application servers are really lightweight, have a look at Payara server or WildFly Swarm, or maybe Open Liberty or Apache TomEE, along with the various other application servers. These servers are very lightweight and are definitely suitable to be run in a Docker container. I hope by now you're convinced that Java EE 8 is indeed the most lightweight enterprise framework currently available. In the next section, we're going to have a look what's new in Java EE 8.
