amaon.api.gateway.lambda.response.gatewayResponse.package.scala

package com.cj.lambda
import collection.JavaConversions._


/**
 * This package object wraps the poorly documented AWS API Gateway return value necessary to proper respond to HTTP requests in an
 * AWS Lambda Scala project
 */
package object gatewayResponse {
     def response(response:ResponseCode, body:String, headers:Map[String, String] = Map()):java.util.Map[String, Object] = {
      mapAsJavaMap(Map(
          "statusCode"-> response.boxed(), 
          "headers"-> mapAsJavaMap(headers).asInstanceOf[java.util.Map[java.lang.Integer, java.lang.Float]], 
          "body"-> body)
        ).asInstanceOf[java.util.Map[java.lang.String, java.lang.Object]]
    }
    
    case class ResponseCode(value:Int){
      def boxed() = {
        Int.box(value)
      }
    }

    val OK = ResponseCode(200)
}

Deploying JVM code to Amazon AWS Lambda with an API Gateway Trigger is poorly documented by Amazon. Most importantly, the API gateway requires a very specific response to no create 500 errors that look like "Execution failed due to configuration error: Malformed Lambda proxy response" or "Internal Server Error". We are required to return a very specific datatype that represents a JSON String before being serialized by Jackson. This is the Scala code that produced the correct map that is required when using the request/response method-handler mechanism such as package.Class::methodToCall.

Usage might look like the following:

package com.cj.demo

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import com.amazonaws.services.lambda.runtime.Context; 
import com.cj.lambda.gatewayResponse._


class Demo{
  
    def myHandler(context:Context ) = {
      response(OK, "David Says Hello to the Agitators")
    }
     
}