My background, which informs my personal taste here:
- Most recent 8 years, have used dynamic languages on the server (Node.js, Ruby, PHP, some Python)
- Have dabbled in C# (ASP.NET MVC and WPF)
- First 4 years professional experience as a Java web developer (servlets, Struts, Spring, Hibernate, etc)
- Have needed recently to generate greenfield Java apps for relatively straightforward CRUD web apps / JSON APIs
I personally would have a hard time going back to Spring or JEE. I initially looked at Play, which is very cool in many respects, but comes with a high complexity/magic level that makes me nervous. Probably it's great, my old bones just can't deal with another long walk to mastery like with Rails.
Here's the stack I have been most comfortable with - note that this has been for relatively simple CRUD app development, and may or may not suit your hyper-enterprise-iot-multitenant-whatever use case:
Web Framework:
Spark 2 (requires Java 8)
http://sparkjava.com/
Kevin likes: Easy to generate single runnable jar, simple route configuration, no heavy abstraction over HTTP (easy to filter, redirect, return status codes, set cookies, etc), support for a variety of modern template engines.
Kevin dislikes: pretty small community around the software
Template Engine:
jade4j
https://github.com/neuland/jade4j
Kevin likes: terse syntax I came to enjoy from Node/Ruby, can easily re-use templates on the front end if needed in Backbone. Integrates easily with Spark.
Model:
Morphia (MongoDB)
http://mongodb.github.io/morphia/
Kevin likes: it's web scale, no schema maintenance, easy to configure for dev/test/prod, easy to create fat models, doesn't require a ton of annotation for persistent fields.
Kevin dislikes: sparse documentation
Dependencies/Build:
Maven (duh)
https://maven.apache.org/
Kevin likes: doesn't matter if I like it, all Java packages live there. Lots to use and choose from both for build tasks and in your code. Make note of the Shade plugin, which makes it easy to generate a single runnable "fat jar":
https://maven.apache.org/plugins/maven-shade-plugin/
Kevin dislikes: OMG XML. Super verbose. Pretty slow. Seems to frequently download the Internet. Not fun to extend - consider shelling out to your own scripts:
http://www.mojohaus.org/exec-maven-plugin/
With the above tools, I found that it's easy to take advantage of the great software packages that do exist for Java, without making my brain hurt too much.
HTH!