Thoughts on Spring Boot

 Having long been a fan of the Spring framework (Spring MVC, Spring Social etc), I have recently started using Spring Boot for two different projects I am currently working on.
In both cases, they are web applications - both with some key differences in technology (in terms of what I am using for client side libraries and data persistence).

Spring Boot is an opinionated implementation of Spring - and it works really nicely (most of the time).  You simply add the Spring Boot dependencies to your build file (Gradle or Maven both well supported) and you can have an application up and running with a very small amount of code (you may have seen the Spring boot application in a Tweet a while ago)

@Controller class ThisWillActuallyRun { @RequestMapping("/") @ResponseBody String home() { "Hello World!" } }
— Rob Winch (@rob_winch) August 6, 2013

Now of course, in reality you do need other configuration stuff, but the take away point is that if you are happy with Spring opinions, you can get an application up and running in pretty quick time.  For me, this is really a turning point for Java/Spring productivity - especially as Groovy has become more mature and sits so easily in Spring Boot, I don't think there is much to the argument that Java/Spring is too slow for early stage companies/prototypes/rapid development process (Aside: I know grails has been around for a while, but I think Spring and Java have stepped up here, plus I honestly have my suspicions that Spring Boot and Grails may clash at some point - they have certainly been on a collision course since Spring Boot was announced at Spring One).


The way it works is quite simple really, you add a relevant dependency to your buildfile, for example:

compile("org.springframework.boot:spring-boot-starter-web")  
compile("org.springframework.boot:spring-boot-starter-thymeleaf")


The first one is just your standard web application Spring Boot dependency, and the second is the opinionated version of Thymeleaf configuration.  Then, at startup Spring Boot has lots of AutoConfiguration files that check for the existence of key classes in the classpath, and if present it executes the auto configuration.

See here for the Thymeleaf autoconfiguration - you will see that there is heavy use of the @ConditionalOnClass annotation - which checks for relevant Thymeleaf classes, and if they are on the classpath it configures them.



Undoubtedly, there are a few times where you find yourself scratching your head at the magic, and I have on more than one occasion had to go through the Spring source code.  And sometimes, you want most of the auto configuration, but just want to tweak one or two properties, and you are left having to turn off the autoconfig and do it yourself, but for me the biggest take away point is the speed at which it is now possible to get up and running with Spring/Java/Groovy and have a decent web platform for building your product or company.