How to create Java microservices with Dropwizard

On Tuesday October 14th the Amsterdam Middleware Meetup experimented with Dropwizard. The idea was to find out what this technology is about, where it could be useful and what the alternatives are. So below I’ll give you an overview of Dropwizard and compare it to Spring Boot. The Dropwizard website claims: Dropwizard pulls together stable, mature libraries from the Java ecosystem into a simple, light-weight package that lets you focus on getting things done. ”¨I’ll discuss each of these claims below. Stable and mature Dropwizard uses Jetty, Jersey, Jackson and Metrics as its most important frameworks, but also a host of other stuff like Guava, Liquibase and Joda Time. The latest Dropwizard release is version 0.7.1, released on June 20th 2014. It depends on these versions of some core libraries: Jetty - 9.2.3.v20140905 - May 2014 Jackson - 2.4.1 - June 2014 Jersey - 2.11 - July 2014 The table shows that stable != out-of-date which is fine of course. The versions of core libraries used are recent though. I guess ‘stable’ means libraries with a long history. Simple The components of a Dropwizard application are shown below (taken from the tutorial https://dropwizard.io/getting-started.html):

1. Application (HelloWorldApplication.java): the applications main method, responsible for startup.
2. Configuration (HelloWorldConfiguration.java) sets configuration for an environment, this is where you may set hostnames for systems the application depends on or set usernames.
3. Data object (Saying.java).
4. Resource (HelloWordResource.java): service implementation entry point
5. Health Check (TemplateHealthCheck.java): runtime tests that show if the application still works.

Light weight We did some experiments trying to answer the question whether Dropwizard applications are light weight. The table below summarizes some of the sizes of deployments and tools. Tomcat size 14 mb Tomcat lib folder size 7 MB Jetty size 14,6 MB Jetty in Dropwizard jar: 5,4 MB Dropwizard tutorial example 10 mb Dropwizard extended example 20 MB Dropwizard Hibernate classes in package: 5 MB A Tomcat or Jetty installation takes about 14 MB, but if you count only the lib folder the size goes down to about 7 MB. The Jetty folder in Dropwizard however is only 5.5 MB. Apparently Dropwizard managed to strip away some code you don’t really need (or is packaged somewhere else, we didn’t look into that). Building the tutorial results in a 10 MB jar, so if you would run a webapp in its own Tomcat container, switching to Dropwizard saves quite a bit. On the other hand, deployment size isn’t all that important if we’re still talking < 50 MB. Compared to your default Weblogic install (513 MB, Weblogic-only on OSX) however, savings are humongous (but this is also true when you compare Weblogic to Tomcat or Jetty). Productivity We tried to run the build for the tutorial application (dropwizard-example in the dropwizard project on Github). This works fine and takes about 8 seconds using mocks for external connections. One option to explore would be to run tests against a deployed application. What we’re used to is that deploying an application for test takes lots of time and resources, but starting a Dropwizard app is quite cheap. Therefore it would be possible to run an integration test of services at the end of a build. This would be quite hard to do with e.g. Weblogic or Websphere. Spring boot Spring boot is interesting, as well as the discussion around the differences between Spring boot and Dropwizard. See https://groups.google.com/forum/#!topic/dropwizard-user/vH1h2PgC8bU The official Spring boot website says: Spring Boot makes it easy to create stand-alone, production-grade Spring based Applications that can you can "just run". We take an opinionated view of the Spring platform and third-party libraries so you can get started with minimum fuss. Most Spring Boot applications need very little Spring configuration. It’s good to see a platform change according to new insights, but still, I remember Rod Johnson saying some ten years ago that J2EE was bloated and complex and Spring was the answer. Now it seems we need Spring boot to make Spring simple? Or is it just that we don’t need application servers anymore to divide resources among processes? Dropwizard and Docker Finally we experimented with running Dropwizard in a Docker container. This can be done with limited effort because Dropwizard applications have such a small number of dependencies. Thomas Kruitbosch will report on this later. References Spring boot: https://projects.spring.io/spring-boot/ Dropwizard: https://dropwizard.io/