Intercept Deserialization in Jackson

Question

I want to hook into Jackson's deserialization to optionally deserialize a different JSON document than the one provided. That seems like a really weird use case so let me explain.

I am using the Amazon SQS Extended client to put messages that are too large for SQS on S3 instead and a message that looks like this through SQS

["com.amazon.sqs.javamessaging.MessageS3Pointer",{"s3BucketName":"my-bucket","s3Key":"f5a0fa29-7f9c-4852-8bbb-53697799efe2"}]

An elastic beanstalk worker is listening to the other end of that which means that those messages are POSTed to a Jersey endpoint my application maintains. Since those messages are POSTed instead of using a SQS receiveMessage call the extended client will not fetch the message from S3 itself.

I was thinking it would be pretty clever to make a custom JsonDeserializer that would look at the message to see if it was an S3 pointer, download that file, and deserialize it. Otherwise, just deserialize the provided message. However, that isn't working out quite as smoothly as I hoped.

Here is what I have so far:

public class SQSS3Deserializer<T> extends JsonDeserializer<T> {
    private static final String s3PointerHeader = "com.amazon.sqs.javamessaging.MessageS3Pointer";
    private Class<T> type;
    private ObjectMapper mapper = new ObjectMapper();

    public SQSS3Deserializer() {
        super();

        type = getParameterizedTypeArgument();
    }

    @Override
    public T deserialize(JsonParser jp, DeserializationContext dc) throws IOException, JsonProcessingException {
        if (jp.isExpectedStartArrayToken()) {
            jp.nextToken();
            if (s3PointerHeader.equals(jp.getValueAsString())) {
                jp.nextToken();
                S3Pointer p = jp.readValueAs(S3Pointer.class);
                return mapper.readValue(S3Utils.getInputStream(p.s3BucketName, p.s3Key), type);
            }
        }

        return jp.readValueAs(type);
    }

    @SuppressWarnings("unchecked")
    protected Class<T> getParameterizedTypeArgument() {
        return (Class<T>) ((ParameterizedType) getClass().getGenericSuperclass()).getActualTypeArguments()[0];
    }

    static private class S3Pointer {
        public String s3BucketName;
        public String s3Key;
    }

}

For each POJO I want to deserialize I'll have to create an empty subclass with the correct generic specialization, for example:

public class POJOS3Deserializer extends SQSS3Deserializer<POJO> {}

I also will need to add the JsonDeserializer annotation to the class

@JsonDeserialize(using=POJOS3Deserializer.class)
public class POJO { ... }

However, doing it this way causes a stack overflow error because it will continually reenter my deserializer when it calls JsonParser.readValueAs() since readValueAs looks at the JsonDeserialize annotation.

So, I have two questions:

1. How do I change this to keep this fairly generic and still have Jackson do most of the heavy lifting of parsing while avoiding that recursive call?
2. Is there a way to remove the need to derive from SQSS3Deserializer for each POJO I want to deserialize this way?

Thanks