HandleRequestCollectionHelper for Quarkus Amazon Lambda

[hamburml]

Description

Hello.

We run several quarkus application as AWS Lambdas. Some are triggered by an AWS Api gateway and some by sqs or sns. A queue can collect some messages and send them via batching to a lambda. In JSON this would look like this if the message has a name and description attribute.

[{"name":"apple","description":"an apple a day..."},{"name":"strawberry","description":"red fruit"}]

A RequestHandler would look like this:

public class FruitsLambda implements RequestHandler<List<Fruit>, Void> {

    @Override
    public Void handleRequest(List<Fruit> fruit, Context context) {
        fruit.forEach(this::printName);
        return null;
    }

    private void printName(Fruit fruit) {
        Log.info(fruit.name());
        Log.info(fruit.description());
    }
}

When this runs sadly an exception occurs.

ERROR [io.qua.ama.lam.run.AbstractLambdaPollLoop] (Lambda Thread (TEST)) Failed to run lambda (TEST): java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class de.hamburml.quarkus.aws.lambda.Fruit (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; de.hamburml.quarkus.aws.lambda.Fruit is in unnamed module of loader io.quarkus.bootstrap.classloading.QuarkusClassLoader @27b71f50)

The ObjectMapper cannot infer the correct type and as fallback uses a LinkedHashMap.

This can be solved with a little trick and this is my enhancement idea...

public abstract class HandleRequestCollectionHelper<INPUT_TYPE, OUTPUT_TYPE> implements RequestHandler<Object, OUTPUT_TYPE> {
    @Inject
    ObjectMapper objectMapper;

    @Override
    public OUTPUT_TYPE handleRequest(Object input, Context context) {
        INPUT_TYPE convertedInput = objectMapper.convertValue(input, this.getCollectionReference());
        this.handle(convertedInput, context);
        return null;
    }

    public abstract TypeReference<INPUT_TYPE> getCollectionReference();

    public abstract OUTPUT_TYPE handle(INPUT_TYPE input, Context context);

}

public class FruitsLambda2 extends HandleRequestCollectionHelper<List<Fruit>, Void> {

    @Override
    public TypeReference<List<Fruit>> getCollectionReference() {
        return new TypeReference<>() { };
    }

    @Override
    public Void handle(List<Fruit> input, Context context) {
        input.forEach(this::printName);
        return null;
    }

    private void printName(Fruit fruit) {
        Log.info(fruit.name());
        Log.info(fruit.description());
    }
}

With HandleRequestCollectionHelper the subclass is forced to implement getCollectionReference so that the ObjectMapper is able to convert the LinkedHashMap to the Collection-Type. If this is done inside a HandleRequestHelper this is hidden from the developer. Maybe getCollectionReference can also be saved with some reflection magic because the type should be already there in the INPUT_TYPE parameter.

HandleRequestCollectionHelper could be added to the amazon-lambda lib. Or maybe automatically used if a Collection-Type is used in first parameter of implementation of RequestHandler-Interface.

I have a simple example here https://github.com/hamburml/quarkus-lambda-handler-with-collection Under src/test are two packages, working and notworking.

Let me know what you think of that.

Thanks
Michael

[quarkus-bot]

/cc @matejvasek (amazon-lambda), @patriot1burke (amazon-lambda)

[hamburml]

@scrocquesel maybe this is also interesting for you

[patriot1burke]

It would be better to change the reader created by the object mapper here:

https://github.com/quarkusio/quarkus/blob/main/extensions/amazon-lambda/runtime/src/main/java/io/quarkus/amazon/lambda/runtime/AmazonLambdaRecorder.java#L59

To use ObjectMapper.readerFor(TypeReference)

[hamburml]

@patriot1burke Do you have an idea how this can be done in the linked class?

[patriot1burke]

Yeah,

quarkus/extensions/amazon-lambda/runtime/src/main/java/io/quarkus/amazon/lambda/runtime/AmazonLambdaRecorder.java

Line 55 in 1323185

Class<?> parameterType = handlerMethod.getParameterTypes()[0];

Type genericType = handlerMethod.getGenericParameterTypes[0];
JavaType javaType = objectMapper.getTypeFactory().constructType(parameterType);
objectReader = new JacksonInputReader(objectMapper.reader(javaType));

I think that will work. Should do the same for the writer too. Also, probably need to handle the case where the handler class is parameterized.