Scala With RESTEasy (JAX-RS)

In the "code club" / "dojo" or whatever you want to call it that Ben (aka Johnny Coder) organized we have been learning about Scala the last few weeks. I have been puttering with Scala on my own for about a year now, and it has been fun to engage with other folk in the learning process. We have mostly been doing a mix of Project Euler and the S-99 problems as exercises. Those problems are fun, but they don't really reflect the kind of day to day programming tasks that I am usually engaged in.

To scratch that slightly more practical itch, I decided to see how well Scala fits in with other tools in the Java ecosystem. The Java ecosystem being broad, and my Scala kung fu being not that strong, all I have are some possibly interesting bits I discovered while trying to get Scala and RESTEasy working together.  I picked RESTEasy because in the middle of reading RESTful Java with JAX-RS.

I started off with an existing example project from chapter 11 in the RESTEasy book. I added the Scala plugin to the maven build, and I was off.

The first class I converted over was a JAXB annotated class com.restfully.shop.domain.Customer

I ran into a few things that caused me problems.  The first was this compiler message:

"';' expected but ',' found"

At the @XMLType annotation line.  The resolution was to switch from using the Array literal "{}" Java syntax to the Scala Array object.

I also got a JAXB runtime error during the JUnit tests:

....
Caused by: com.sun.xml.bind.v2.runtime.IllegalAnnotationsException: 15 counts of IllegalAnnotationExceptions
There are two properties named ....

I resolved that by using the @XmlAccessorType(XmlAccessType.FIELD) annotation.

For compatibility with the existing code that expected Java Bean style property access, I added the @BeanProperty annotation.   The annotation causes Scala to automatically generate get/set methods.

Here is the java version of Customer:

package com.restfully.shop.domain;

import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlType;

@XmlRootElement(name = "customer")
@XmlType(propOrder = {"firstName", "lastName", "street", "city", "state", "zip", "country"})
public class Customer
{
   private int id;
   private String firstName;
   private String lastName;
   private String street;
   private String city;
   private String state;
   private String zip;
   private String country;

   @XmlAttribute
   public int getId()
   {
      return id;
   }

   public void setId(int id)
   {
      this.id = id;
   }

   @XmlElement(name = "first-name")
   public String getFirstName()
   {
      return firstName;
   }

   public void setFirstName(String firstName)
   {
      this.firstName = firstName;
   }

   @XmlElement(name = "last-name")
   public String getLastName()
   {
      return lastName;
   }

   public void setLastName(String lastName)
   {
      this.lastName = lastName;
   }

   @XmlElement
   public String getStreet()
   {
      return street;
   }

   public void setStreet(String street)
   {
      this.street = street;
   }

   @XmlElement
   public String getCity()
   {
      return city;
   }

   public void setCity(String city)
   {
      this.city = city;
   }

   @XmlElement
   public String getState()
   {
      return state;
   }

   public void setState(String state)
   {
      this.state = state;
   }

   @XmlElement
   public String getZip()
   {
      return zip;
   }

   public void setZip(String zip)
   {
      this.zip = zip;
   }

   @XmlElement
   public String getCountry()
   {
      return country;
   }

   public void setCountry(String country)
   {
      this.country = country;
   }

   @Override
   public String toString()
   {
      return "Customer{" +
              "id=" + id +
              ", firstName='" + firstName + '\'' +
              ", lastName='" + lastName + '\'' +
              ", street='" + street + '\'' +
              ", city='" + city + '\'' +
              ", state='" + state + '\'' +
              ", zip='" + zip + '\'' +
              ", country='" + country + '\'' +
              '}';
   }
}

Here is my Scala conversion of Customer:

package com.restfully.shop.domain

import javax.xml.bind.annotation.XmlAttribute
import javax.xml.bind.annotation.XmlElement
import javax.xml.bind.annotation.XmlRootElement
import javax.xml.bind.annotation.XmlType
import javax.xml.bind.annotation.XmlAccessorType
import javax.xml.bind.annotation.XmlAccessType

import scala.reflect.BeanProperty

@XmlRootElement(name = "customer")
@XmlType(propOrder = Array("firstName", "lastName", "street", "city", "state", "zip", "country"))
@XmlAccessorType(XmlAccessType.FIELD)
class Customer {

   @XmlAttribute
   @BeanProperty
   var id: Int = _
   
   @XmlElement(name = "first-name")
   @BeanProperty
   var firstName: String = _
   
   @XmlElement(name = "last-name")
   @BeanProperty
   var lastName: String = _
   
   @XmlElement
   @BeanProperty
   var street: String = _
   
   @XmlElement
   @BeanProperty
   var city: String = _
   
   @XmlElement
   @BeanProperty
   var state: String = _
   
   @XmlElement
   @BeanProperty
   var zip: String = _

   @XmlElement
   @BeanProperty
   var country: String = _

   override def toString = 
    "Customer{" +
    "id=" + id +
    ", firstName='" + firstName + '\'' +
    ", lastName='" + lastName + '\'' +
    ", street='" + street + '\'' +
    ", city='" + city + '\'' +
    ", state='" + state + '\'' +
    ", zip='" + zip + '\'' +
    ", country='" + country + '\'' +
    '}'
   
}

The next class I converted was com.restfully.shop.domain.Customers

This conversion was very similar, but it was dealing with collections.  I found that Scala 2.8 has a new object scala.collection.JavaConversions that contains many implicit conversion for Java collections. 

Here is the Java version of Customers:

package com.restfully.shop.domain;

import javax.xml.bind.annotation.XmlElementRef;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.XmlTransient;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

/**
 * @author Bill Burke
 * @version $Revision: 1 $
 */
@XmlRootElement(name = "customers")
public class Customers
{
   protected Collection customers = new ArrayList();
   protected List links;

   @XmlElementRef
   public Collection getCustomers()
   {
      return customers;
   }

   public void setCustomers(Collection customers)
   {
      this.customers = customers;
   }

   @XmlElementRef
   public List getLinks()
   {
      return links;
   }

   public void setLinks(List links)
   {
      this.links = links;
   }

   @XmlTransient
   public String getNext()
   {
      if (links == null) return null;
      for (Link link : links)
      {
         if ("next".equals(link.getRelationship())) return link.getHref();
      }
      return null;
   }

   @XmlTransient
   public String getPrevious()
   {
      if (links == null) return null;
      for (Link link : links)
      {
         if ("previous".equals(link.getRelationship())) return link.getHref();
      }
      return null;
   }

}

Here is my Scala conversion of Customers:

package com.restfully.shop.domain

import java.util.{ArrayList => JArrayList}
import java.util.{Collection => JCollection}
import java.util.{List => JList}

import javax.xml.bind.annotation.XmlElementRef
import javax.xml.bind.annotation.XmlRootElement
import javax.xml.bind.annotation.XmlTransient
import javax.xml.bind.annotation.XmlAccessorType
import javax.xml.bind.annotation.XmlAccessType

import scala.collection.Iterable
import scala.collection.JavaConversions._
import scala.collection.mutable.Buffer

@XmlRootElement(name = "customers")
@XmlAccessorType(XmlAccessType.PROPERTY)
class Customers {

  var customers = Iterable[Customer]() 
  var links: Buffer[Link] = Buffer()
  
  @XmlElementRef
  def getCustomers: JCollection[Customer] = customers
  def setCustomers(customers: JCollection[Customer]) = {
    this.customers = customers
  }
 
  @XmlElementRef
  def getLinks: JList[Link] = links
  def setLinks(links: JList[Link]) = {
    this.links = links
  }
  
  @XmlTransient
  def getNext(): String = findHref("next")
 
  @XmlTransient
  def getPrevious(): String = findHref("previous")
  
  private def findHref(rname: String): String = {
    val rel = links.filter(_.getRelationship == rname)
    rel match {
      case Buffer() => null
      case _        => rel.head.getHref
    }
  }
  
}

That’s about as far as I got this weekend.  I guess I was actually mostly working with JAXB this time.  The same example code has JPA as was as JAX-RS, and I’m going to try and convert the entire project to Scala, and if I do, I’ll upload it to BitBucket.