‘Polymorph-EE-c’ a.k.a Java EE avatars

Polymorphism + Java EE = Polymorph-EE-c

This post covers the various avatars of Java EE containers of various shapes, sizes and flavours !

Good old ‘full-blown’ application server

• Java EE Full Profile : everything you need !
• Tried, tested and successful for years in enterprises as well as start ups

The Java EE Web Profile

• Stripped down version of the full Java EE stack
• Support for limited (yet significant) Java EE APIs. The list of specifications is available in section WP.2.1 of the Web Profile specification document 
• Vendors can choose to be compliant with only the Web Profile (e.g. Apache TomEE) or provide additional API support on top of the pre-defined list in the Web Profile

Embedded app servers

• The app server as a library concept allows you to launch a Java EE container as a process from existing Java code using specific APIs (not very different from putting another JAR in your classpath)
• Examples: Glassfish is the most prominent example of an embedded container
• Advantages: Good for testing, no setup/installation needed,

Embedded versions of Java EE APIs

• Some of the Java EE APIs specifications support execution in an embedded mode. What this means is that instead of using a Java EE (full or web profile) container, one can just leverage the services of a specific technology. This is generally achieved by using the specification centric library (JAR) invoking a bootstrap API (to be invoked by your Java code) which launches the container inside the same JVM – think of it as another (Java) process
• Embeddable API examples: EJB (OpenEJB), CDI (Weld, OpenWebBeans), Servlet (Jetty, Undertow)

Micro and BYOR (Build Your Own Runtime) frameworks

• These are lightweight breed of containers which revolves around the notion of supporting a limited set of specific APIs (in a pre-defined or flexible manner)
• Relatively new & fuelled by microservices, Docker etc.
• The BYOR style frameworks (e.g. Wildfly Swarm, KumuluzEE) allow you to pick and choose different Java EE APIs as per your requirements, build a fat JAR and kick start your application using java -jar 
• As far as Micro mode is concerned, I am only aware of Payara Micro. Here is a previous blog post on this topic
• Similarities b/w Micro & BYOR: both embrace java -jar style
• Differences b/w Micro & BYOR: Micro version has pre-defined set of APIs as opposed to a more modular approach followed by BYOR style solutions

Have you seen/used Java EE in other avatars? Drop in a comment

Cheers!