How to call Grails from Scala

Is there a way to call a method in a Grails service, from a Scala class that is running on the same JVM? I have see开发者_如何学JAVAn something similar done from Groovy/Griffon but cannot figure out how to accomplish that in Grails. (http://www.jroller.com/aalmiray/entry/griffon_groovy_scala_working_together)

Basically, one of my Grails controllers calls some Scala code, which should return some values asynchronously. So, I guess, the only way to return those values is by calling back a method in a Grails service.

I found a way of doing it, inspired by the link in the question above, and one of the FAQs in the Grails website.

On the Scala side: Declare an object similar to the following:

package scalaCallback

object ScalaCallback{
    var cback: {def callback(example: String)} = null

    def setCallback(cb: {def callback(example: String)}){
        cback = cb
    }

    def invokeCallback(example: String){
        if(callback != null) cback.callback(example)
    }
}

On the Grails side:

Create a class in src/groovy similar to the following:

package groovyCallback
import org.codehaus.groovy.grails.commons.ApplicationHolder

class GroovyCallback{
    private GroovyCallback() {}
    private static final INSTANCE = new GroovyCallback()

    static getInstance(){ return INSTANCE }

    void callback(String example){
        ApplicationHolder.application.mainContext.yourService.yourMethod(example)   
    }
}

In your BootStrap.groovy init add the following:

scalaCallback.cback = groovyCallback.GroovyCallback.getInstance()

When you call invokeCallback("example") in Scala, it will call yourService.yourMethod("example")

Note: the jar file with your Scala class should be in the lib folder of you Grails application

Your Grails service is a Spring bean. @Autowire the service into your Scala class (it will need to be a bean/@Component) and call the method.

EDIT - added example:

For example (using Java, not Scala but the approach is exactly the same):

Java code calling service:

package grailstest;

@Component
public class ServiceInjectionTester {
    @Autowired TestService testService;

    public String testTheService() {
        return testService.serviceMethod();
    }
}

Service:

class TestService {
    String serviceMethod() {
        return "success"
    }
}

In Config.groovy:

grails.spring.bean.packages = [ "grailstest" ]

You can also wire your Java/Scala bean into your Grails classes:

class TestController {
    @Autowired
    ServiceInjectionTester serviceInjectionTester

    def index = { 
        render(text: serviceInjectionTester.testTheService())
    }
}

References:

Grails Reference 8.4 - Using Services from Java

Spring: The Foundation for Grails