tisdag 12 november 2013

Love is in the details. Or when I really fell in love with Dropwizard

So Dropwizard seems to be the rage around Java / Scala developers today as an extremely clean and minimalistic framework for DTRS ("Doing The Right Stuff") when it comes to serving up thick clients with REST-ful data. If you haven't checked it out yet, I urge you to.
It is really one of those few frameworks that looks so shiny and sexy that you immediately start thinking about in which of your projects you could introduce it. The last time I was this enthustiastic about a new library was when I first laid my eyes on Camel, which shares the same minimalistic mindset.

Now, a lot has been said about it's excellent choice of best-of-breeds libraries, the YAML configuration, server-less environment and the ability to quickly assemble healtchecks. But the tiny one thing that made me realize that the folks at Yammer really put in a lot of thought into the package was not as profound as the above points. It was a really small feature that simply tells you that these guys has been in the trenches and know what they're doing. Now, which of all features could that be?

Error logging...

As I started to play around with a small hello world hobby project and got my first 500 error back at me it said something like:

"There was an error processing your request. It has been logged (ID 2e7c06aac7bcf2aa)."

Looking into the server logs I see a stacktrace with the same ID appended:

 ERROR [2013-11-12 11:18:23,651] com.yammer.dropwizard.jersey.LoggingExceptionMapper: Error handling a request: 2e7c06aac7bcf2aa  
 ! java.lang.RuntimeException: My extremely PITA error  
 ! at se.com.eyc.employeecatalog.EmployeeCatalogue.allEmployees(EmployeeCatalogue.java:38) ~[dropwizard.jar:na]  
 ! at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.6.0_45]  
 ! at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) ~[na:1.6.0_45]  
 ! at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) ~[na:1.6.0_45]  
 ! at java.lang.reflect.Method.invoke(Method.java:597) ~[na:1.6.0_45]  
 ! at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) ~[jersey-server-1.17.1.jar:1.17.1]  
 ! at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185) ~[jersey-server-1.17.1.jar:1.17.1] ! at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) ~[jersey-server-1.17.1.jar:1.17.1]  
 ! at com.yammer.dropwizard.jersey.OptionalResourceMethodDispatchAdapter$OptionalRequestDispatcher.dispatch(OptionalResourceMethodDispatchAdapter.java:37) ~[dropwizard-core-0.6.2.jar:na]  
 ! at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302) ~[jersey-server-1.17.1.jar:1.17.1]  
 ! at com.sun.jersey.server.impl.uri.rules.ResourceObjectRule.accept(ResourceObjectRule.java:100) ~[jersey-server-1.17.1.jar:1.17.1]  
 ! at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) ~[jersey-server-1.17.1.jar:1.17.1]  

Now this is great handing out of the box for three reasons:
  • Your customer / client system has an ID they can refer to which you can find with a simple grep in the logs
  • The default behaviour in DW is to NOT hand your stacktrace to your clients (unlike say a plain Tomcat among others). I can not believe that you still today sometimes see customer facing sites with no configured error page. That actually happened to me just a couple of days ago when a pretty big web shop happily informed me that they had not tweaked their connection pool for the MySQL database in the backend. This is just sloppy and DW simply does the right thing for you out of the box.
  • The stacktrace actually contains the artifact id and version of the dependencies that was involved in the stack. This is pure genious as it helps tremendesly i.e. when you submit bugs since everyone can easily see which versions of what you were using.
So, just a small example why I think DW rocks and proves that the guys who built it knows what they're doing. It seems to be a stable foundation to build your next web app or service on. I sincerely hope that it can stay out of the typical OS feature creep and stay simple and lean.

Til next time!

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