Scala, #ResponseBody, and Map - spring

Question

I'm experimenting with Scala in a spring3 project, and I'm not getting what I expect when I return a map with #ResponseBody. I'm including a working example in java along with my attempt in scala
// This is Java
#RequestMapping(value="/pbx.admin", method=RequestMethod.GET)
public #ResponseBody Map<String, Object> getInfo2(HttpServletRequest request, Model model){
Map<String, Object> map = new HashMap<String, Object>();
map.put("pbx", "admin");
map.put("method", "s");
return map;
}
The java returns json with the pbx & method defined, which is what I'm expecting.
// This is Scala
#RequestMapping(value= Array("/pbx.admin"),
method=Array(RequestMethod.GET))
#ResponseBody
def getInfo2() = {
Map("pbx" -> "admin", "method" -> "s")
}
The scala returns something different though:
{
empty: false,
traversableAgain: true
}
What do I need to do in order to get my map keys / values?
And for extra credit, Is there a better 'scala way' to do this? Thanks!

Answer 1

Spring MVC framework wasn't built with Scala in mind and it doesn't recognize Scala's Map. You must convert scala.collection.Map to java.util.Map. You can either use implicit conversion:
import collection.JavaConversions._
def getInfo2(): java.util.Map[String, String] = {
Map("pbx" -> "admin", "method" -> "s")
}
or convert it manually:
import collection.JavaConverters._
def getInfo2() = {
Map("pbx" -> "admin", "method" -> "s").asJava
}
Mind the imports, they are important.
I suspect Spring can be hacked to accept Scala collections, but obviously not out-of-the box.

Answer 2

Spring MVC uses Jackson. You need to register the Jackson scala module as a mapper. This adds support for scala to Jackson allowing it to recognize the collections.
Example:
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.ScalaModule
import com.fasterxml.jackson.module.scala.DefaultScalaModule
class ScalaObjectMapper extends ObjectMapper {
{
registerModule(DefaultScalaModule)
}
}
Then you need to add it to you message converters
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper">
<bean class="com.petzfactor.packwall.web.module.ScalaObjectMapper"></bean>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
The module is on github at https://github.com/FasterXML/jackson-module-scala

Answer 3

Scala module is required to serialize scala objects such as Collections, Option and case classes. Here is a way to register the Jackson Scala module only by modifying the Spring context.
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper" ref="objectMapperWithScala"/>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
<bean name="scalaModule" class="com.fasterxml.jackson.module.scala.DefaultScalaModule"/>
<bean name="objectMapper" class="com.fasterxml.jackson.databind.ObjectMapper"/>
<bean name="objectMapperWithScala" factory-bean="objectMapper" factory-method="registerModule">
<constructor-arg ref="scalaModule"/>
</bean>