Tuesday, April 29, 2014

Spring Boot and Scala with sbt as the build tool

Earlier I had blogged about using Scala with Spring Boot and how the combination just works. There was one issue with the previous approach though - the only way to run the earlier configuration was to build the project into a jar file and run the jar file.

./gradlew build
java -jar build/libs/spring-boot-scala-web-0.1.0.jar

Spring boot comes with a gradle based plugin which should have allowed the project to run with a "gradle bootRun" command, this unfortunately gives an error for scala based projects.

EDIT: This is actually not completely true, another way to run the Spring-boot code using gradle will be to use the gradle application plugin and specify the main program this way:
apply plugin:'application'
mainClassName = "mvctest.SampleWebApplication"

A good workaround is to use sbt for building and running Spring-boot based projects. The catch though is that with gradle and maven, the versions of the dependencies would have been managed through a parent pom, now these have to be explicitly specified. This is how a sample sbt build file with the dependencies spelled out looks:

name := "spring-boot-scala-web"

version := "1.0"

scalaVersion := "2.10.4"

sbtVersion := "0.13.1"

seq(webSettings : _*)

libraryDependencies ++= Seq(
  "org.springframework.boot" % "spring-boot-starter-web" % "1.0.2.RELEASE",
  "org.springframework.boot" % "spring-boot-starter-data-jpa" % "1.0.2.RELEASE",
  "org.webjars" % "bootstrap" % "3.1.1",
  "org.webjars" % "jquery" % "2.1.0-2",
  "org.thymeleaf" % "thymeleaf-spring4" % "2.1.2.RELEASE",
  "org.hibernate" % "hibernate-validator" % "5.0.2.Final",
  "nz.net.ultraq.thymeleaf" % "thymeleaf-layout-dialect" % "1.2.1",
  "org.hsqldb" % "hsqldb" % "2.3.1",
  "org.springframework.boot" % "spring-boot-starter-tomcat" % "1.0.2.RELEASE" % "provided",
  "javax.servlet" % "javax.servlet-api" % "3.0.1" % "provided"
)


libraryDependencies ++= Seq(
  "org.apache.tomcat.embed" % "tomcat-embed-core"         % "7.0.53" % "container",
  "org.apache.tomcat.embed" % "tomcat-embed-logging-juli" % "7.0.53" % "container",
  "org.apache.tomcat.embed" % "tomcat-embed-jasper"       % "7.0.53" % "container"
)

Here I am also using xsbt-web-plugin which is plugin for building scala web applications.

xsbt-web-plugin also comes with commands to start-up tomcat or jetty based containers and run the applications within these containers, however I had difficulty in getting these to work.

What worked is the runMain command to start up the Spring-boot main program through sbt:

runMain mvctest.SampleWebApplication

and xsbt-web-plugin allows the project to be packaged as a war file using the "package" command, this war deploys and runs without any issues in a standalone tomcat container.

Here is a github project with these changes: https://github.com/bijukunjummen/spring-boot-scala-web.git

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