Basic WS with Scala

I recently had a chance to work on building SOA platforme using JEE 6 and Scala language. I will share here some snippets my be helpfull to start publishing web services using Scala, Sbt and JAX-WS. Consider the example to calculate the quotient and remainder using euclidean algorithm. Not very complexe if the inputs are positives numbers.

I- Sbt

Let’s create an sbt projet and add required dependencies

$ mkdir sws $ cd sws $ touch build.sbt $ edit build.sbt as following :

name := "Euclide"

version := "1.0"

organization := "me.ouertani"

scalaVersion := "2.9.1"

scalaSource in Compile <<= baseDirectory(_ / "src")

scalaSource in Test <<= baseDirectory(_ / "test")

libraryDependencies += "javax" % "javaee-api" % "6.0" % "provided"

libraryDependencies += "log4j" % "log4j" % "1.2.16" % "provided"

libraryDependencies += "junit" % "junit" % "4.8.2" % "test"

$ mkdir src $ touch src/Euclide.scala

That’a all for project configuration.

II- Create the WS

We will use a single Euclide.scala file for all class this will be easier for visibility

• Create a Request Class and don’t forget :
  1. default constructor
  2. field access annotation

@XmlAccessorType(XmlAccessType.FIELD)
case class Request(a : Int, b : Int ){ def this(){this(0,0)}}

1. Create a Response Class

   @XmlAccessorType(XmlAccessType.FIELD)
   @XmlType(name = "output")
   case class Response (c: Int, d: Int){ def this(){this(0,0)}}
   

2. Why not to create an exception class to handle exceptions like b is equal to 0 ```scala @XmlAccessorType(XmlAccessType.FIELD) case class ResponseException(why : String){ def this(){this(“”)}}

@XmlAccessorType(XmlAccessType.FIELD) case class FaultResponse(@BeanProperty faultInfo : ResponseException) extends Exception { def this(){this(ResponseException(“”))}}

Don’t forget to add BeanProperty annotation to faultInfo input !

5. Let’s add an interceptor to log all ws method call

```scala
object TracingInterceptor{
  import org.apache.log4j.Logger
  val L = Logger.getLogger(classOf[TracingInterceptor])
}

import TracingInterceptor._
class TracingInterceptor {

  @AroundInvoke
  def  log( context:InvocationContext):Object ={
    try {
      if (L.isDebugEnabled()) {
        val clazz = context.getMethod().getDeclaringClass().getName()
        val method = context.getMethod().getName()        
        L.debug(clazz + " : Is invoking method: " + method + " With Parameters : " + context.getParameters().mkString("[", ",","]"))
      }
    } catch {
      case  ex :Exception =>    L.warn("Unable to Intercept Method Call", ex)
    }
    context.proceed()
  }
}

1. The WS class and it’s divide method using intercpetor and stateless EJB 3.1

   @WebService(serviceName = "Euclide", targetNamespace = "http://slim.ouertani.me/")
   @Stateless()
   @Interceptors(Array(classOf[TracingInterceptor]))
   class Euclide {
     @throws(classOf[FaultResponse])
     def divide( @WebParam(name="input" )  @XmlElement(required = true, nillable = false)
    req :Request):Response =  req match {
      case Request(_, 0 ) => throw FaultResponse(ResponseException("Can't divide by ZERO!"))
      case Request(a, b ) =>  Response(a / b ,a % b)
    }
   }
   

2. Don’t forget package , imports at the head of file and it’s all:

package me.ouertani.scala.ws

import javax.interceptor.Interceptors
import javax.xml.bind.annotation.XmlElement
import javax.interceptor.{ AroundInvoke , InvocationContext }
import javax.xml.bind.annotation. { XmlAccessType , XmlAccessorType, XmlElement, XmlType}
import javax.ejb. { EJB ,Stateless }
import javax.jws. {WebService , WebParam }
import scala.reflect.BeanProperty

III- packaging and run WS

1. Let’s start compiling our projet
$ xsbt compile
2. package the jar
$ xsbt package
3. deploy it to your JEE 6 container ( mine is Glassfish 3.1.1 )

IV – test it

1- After depoyed let’s test it using soapUI tool Request 1

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:slim="http://slim.ouertani.me/">
   <soapenv:Header/>
   <soapenv:Body>
      <slim:divide>
         <input>
            <a>6</a>
            <b>4</b>
         </input>
      </slim:divide>
   </soapenv:Body>
</soapenv:Envelope>

Response 1 :

<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
   <S:Body>
      <ns2:divideResponse xmlns:ns2="http://slim.ouertani.me/">
         <return>
            <c>3</c>
            <d>0</d>
         </return>
      </ns2:divideResponse>
   </S:Body>
</S:Envelope>

Request 2 :

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:slim="http://slim.ouertani.me/">
   <soapenv:Header/>
   <soapenv:Body>
      <slim:divide>
         <input>
            <a>6</a>
            <b>0</b>
         </input>
      </slim:divide>
   </soapenv:Body>
</soapenv:Envelope>

Response 2 :

<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
   <S:Body>
      <S:Fault xmlns:ns4="http://www.w3.org/2003/05/soap-envelope">
         <faultcode>S:Server</faultcode>
         <faultstring>me.ouertani.scala.ws.FaultResponse</faultstring>
         <detail>
            <ns2:FaultResponse xmlns:ns2="http://slim.ouertani.me/">
               <faultInfo>
                  <why>Can't divide by ZERO!</why>
               </faultInfo>
            </ns2:FaultResponse>
         </detail>
      </S:Fault>
   </S:Body>
</S:Envelope>

Fine!