Using Vaadin with Scala

Scala is a multi-paradigm language integrating object-oriented and functional programming. Read more about Scala on http://www.scala-lang.org.

Getting ready

Scala installation is quite easy. Just go to http://www.scala-lang.org/downloads, download Scala, and set up system variables as follow:

• Linux/Mac

  SCALA_HOME=/Users/John/Installations/scala
  export SCALA_HOME
  export PATH=$PATH:$SCALA_HOME/bin
  

• Windows

  %SCALA_HOME% = c:\Scala
  %PATH% = %PATH%;%SCALA_HOME%\bin
  

We have to maintain our project anyhow and we are going to utilize Gradle.

Tip

There is also another way to manage Scala projects. It is called Typesafe and more info is on http://typesafe.com.

How to do it...

Carry out the following steps in order to create a new Scala project:

1. Make the project structure so we have folders where we can put our project files.

   mkdir -p vaadin-in-scala/src/main/{scala/app,webapp/WEB-INF}
   

2. Make build.gradle in the project root. It is going to be just a few lines that are necessary for running the project.

   apply plugin: 'war'
   apply plugin: 'jetty'
   apply plugin: 'scala'
       
   repositories {
     mavenCentral()
   }
       
   dependencies {
     scalaTools 'org.scala-lang:scala-compiler:2.10.0'
     scalaTools 'org.scala-lang:scala-library:2.10.0'
     compile 'org.scala-lang:scala-library:2.10.0'
     compile group:'com.vaadin', name:'vaadin-server', version:'7.0.4'
     compile group:'com.vaadin', name:'vaadin-client', version:'7.0.4'
     compile group:'com.vaadin', name:'vaadin-client-compiled', version:'7.0.4'
     compile group:'com.vaadin', name:'vaadin-themes', version:'7.0.4'
     compile group:'com.vaadin', name:'vaadin-client-compiler', version:'7.0.4'
   }
   

3. Create a new Scala class MyVaadinUI that we place into the MyVaadinUI.scala file in the folder src/main/scala/app.

   package app
   
   import com.vaadin.ui._
   import com.vaadin.server.VaadinRequest
   
   class MyVaadinUI extends UI {
     def init(request: VaadinRequest) = {
       val layout = new VerticalLayout()
       layout.setMargin(true)
       setContent(layout)
       layout.addComponent(new Label("Hello Vaadin user."))
       }
   }

4. Add the web.xml file to the src/main/webapp/WEB-INF folder.

   <?xml version="1.0" encoding="UTF-8"?>
   <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
     <display-name>Vaadin Web Application</display-name>
     <context-param>
       <description>Vaadin production mode</description>
       <param-name>productionMode</param-name>
       <param-value>false</param-value>
     </context-param>
     <servlet>
       <servlet-name>Vaadin Application Servlet</servlet-name>
       <servlet-class>com.vaadin.server.VaadinServlet</servlet-class>
       <init-param>
         <description>Vaadin UI to display</description>
         <param-name>UI</param-name>
         <param-value>app.MyVaadinUI</param-value>
       </init-param>
     </servlet>
     <servlet-mapping>
       <servlet-name>Vaadin Application Servlet</servlet-name>
       <url-pattern>/*</url-pattern>
     </servlet-mapping>
   </web-app>

5. We are done and we can run the application.

   gradle jettyRun
   

   The following output should be displayed:

   :compileJava UP-TO-DATE
   :compileScala UP-TO-DATE
   :processResources UP-TO-DATE
   :classes UP-TO-DATE
   > Building > :jettyRun > Running at http://localhost:8080/vaadin-in-scala
   

   

Tip

Downloading the example code

You can download the example code files for all Packt books you have purchased from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

How it works...

We have made a Gradle project in which we have applied the scala plugin. The Scala plugin inside the Gradle build script ensures that all the .scala files inside the src/main/scala source folder will be compiled. Scala files are compiled to .class files that are then deployed on the Jetty webserver.

The deployment descriptor (web.xml file) defines one servlet. When users access the URL with the /* pattern, which is mapped to the Vaadin servlet, MyVaadinUI is shown in the browser.

The important thing we need to check is the init-param element of the Vaadin servlet. It needs to point exactly to the UI class, which represents our application. The path to the UI class must be the full name of the class together with the package, for example, app.MyVaadinUI.

See also

• Scaladin is a Vaadin add-on that makes using Vaadin with the Scala language easier. More information can be found on the Scaladin add-on page at https://vaadin.com/directory#addon/scaladin.