What else makes an enterprise technology lightweight besides the productiveness of the API? What about the runtime, the enterprise container?

Developers often complained about J2EE application servers being too slow, too cumbersome, and unwieldy to use. Installation sizes and memory consumption were quite high. Typically, a lot of applications ran on a server instance in parallel with being redeployed individually. This approach sometimes introduced additional challenges, such as classloader hierarchy issues.

Modern application servers are far from this negative image. Most of them have been heavily optimized for startup and deployment time. Especially, server-internal module approaches such as Open Service Gateway Initiative (OSGi) tackled the necessity of supporting the full Java EE API by loading required modules on demand and greatly speeding up operations. In terms of resource usage, application servers also greatly improved compared to the past. A modern container consumes less memory than a running browser instance on a desktop computer. For example, an Apache TomEE instance starts up in one second, consumes less than 40 megabytes on disk and less than 30 megabytes of memory.

The performance overhead of managed beans is equally negligible. In fact, compared to CDI managed beans and other frameworks such as Spring Framework, stateless EJBs show the best results. This is due to the fact that stateless session beans are pooled and reused after their business methods have been invoked.

Besides that, application servers manage pools of connections and threads and they enable engineers to gather statistics and performance insights out of the box. The container is responsible for providing monitoring for these aspects. DevOps engineers have the possibility to directly use this data without introducing custom metrics.

Besides these aspects, the application servers also manage the bean instances and life cycles, resources, and database transactions, as we have seen in the previous chapter.

This is the point of having an application container. It does the required work to run an enterprise application in production; the software engineers are responsible for dealing with the business logic. The container provides and manages the required resources and is forced by the standards to provide insights into deployed applications. Due to the vendors that put a lot of effort into optimizing the required technologies, the resource overhead can be kept low.

Application servers' installation sizes are still somewhat bigger than other enterprise frameworks. As of writing this book, vendors are striving to provide smaller, on-demand runtimes tailored for the application's needs. The MicroProfile initiative includes several application server vendors that define additional enterprise profiles complementary to the Java EE umbrella. These profiles are assembled from Java EE standards as well. This is a very interesting approach for developers since it doesn't require any change on the application side. The runtime, that is, the set of standards included, will be fitted to what the application needs in order to fulfill its business logic.