aws-lambda handler with InputStream com.fasterxml.jackson.databind.JsonMappingException: Can not construct instance of java.io.InputStream - serialization

Question

I put my AWS Lambda behind API gateway, and now trying to make an end-to-end call.
import java.io.InputStream
import com.amazonaws.services.lambda.runtime.{Context, RequestHandler}
import com.fasterxml.jackson.databind
case class MyClass(a: String, b: String)
class MyHandler extends RequestHandler[InputStream, Boolean] {
val scalaMapper: databind.ObjectMapper = {
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.DefaultScalaModule
new ObjectMapper().registerModule(new DefaultScalaModule)
}
def handleRequest(input: InputStream, context: Context): Boolean = {
val myClass = scalaMapper.readValue(input, classOf[MyClass])
isValid(myClass)
}
It works when I test locally by providing the handler with a string, but when in a Lambda, the handler can't use the input stream. I'm getting the error
Endpoint response body before transformations: {
"errorMessage":"An error occurred during JSON parsing",
"errorType":"java.lang.RuntimeException",
"stackTrace":[],
"cause": {
"errorMessage":"com.fasterxml.jackson.databind.JsonMappingException:
Can not construct instance of java.io.InputStream,
problem: abstract types either need to be mapped to concrete types, have custom deserializer, or be instantiated with additional type information\n
at [Source: lambdainternal.util.NativeMemoryAsInputStream#2698dc7; line: 1, column: 1]",...

Answer 1

A Java Lambda has two possible signatures:
public interface RequestHandler<I, O> {
public O handleRequest(I input, Context context);
}
and
public interface RequestStreamHandler {
public void handleRequest(InputStream input, OutputStream output, Context context) throws IOException;
}
I'm not sure if you're trying to mix the two but you're trying to tell Lambda to deserialize an InputStream.
While I try hard not to do anything in Scala, I believe you want:
case class MyClass(a: String, b: String)
class MyHandler extends RequestStreamHandler {
val scalaMapper: databind.ObjectMapper = {
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.scala.DefaultScalaModule
new ObjectMapper().registerModule(new DefaultScalaModule)
}
def handleRequest(input: InputStream, output: OutputStream context: Context): Unit = {
val myClass = scalaMapper.readValue(input, classOf[MyClass])
output.write( isValid(myClass) )
}
Though I have not tested this. Another, perhaps better way would be:
case class MyClass(a: String, b: String)
class MyHandler extends RequestHandler[MyClass, Boolean] {
def handleRequest(myClass: MyClass, context: Context): Boolean = {
isValid(myClass)
}