AWS DynamoDB trigger using Lambda in JAVA

Question

I am trying to trigger an AWS lambda function written in Java, on dynamodb stream events. Amazon has a guide for the same, using NodeJS here http://docs.aws.amazon.com/lambd

Answer 1

Your code caused the following exception in CloudWatch log,

Class does not implement an appropriate handler interface....

Once I changed the code to the following, I can get the SNS message just fine.

public class RecomFunction implements RequestHandler<SNSEvent, Void> {

    public Void handleRequest(SNSEvent event, Context context) {

        ...
        return null;
    }

}

Answer 2

This worked for me - case DynamoDB stream events:

import com.amazonaws.services.lambda.runtime.RequestHandler;
...

public class DynamoStreamHandler implements RequestHandler<Object, Void> {
    @Override
    public Void handleRequest(Object o, Context context) {

        LinkedHashMap lhm = (LinkedHashMap) o;
        ...etc.
    }
}

It seems they use a customized JSON mapper which utilizes Map and List objects. It's quite straightforward (but tedious) to verify this for other event types by testing and print-outing logs. (sigh)

EDIT: If ~5 MB overhead is ok, you can use DynamodbEvent.DynamodbStreamRecord provided by aws-lambda-java-events library v1.1.0 as described in AWS Lambda Walkthrough 3: Process Amazon DynamoDB Events (Java) in AWS Lambda Documentation.

Answer 3

This code worked for me. You can use it to receive and process DynamoDB events in a Lambda function -

public class Handler implements RequestHandler<DynamodbEvent, Void> {

    @Override
    public Void handleRequest(DynamodbEvent dynamodbEvent, Context context) {

        for (DynamodbStreamRecord record : dynamodbEvent.getRecords()) {

            if (record == null) {
                continue;
            }

            // Your code here
        }

        return null;
    }
}

Similarly, you can use SNSEvent and SNSRecord to handle Amazon SNS events.

Answer 4

To obtain the deserialized objects from event handler : 1) In the handler get json from input stream using something like this :

private String getJsonFrom(InputStream stream) throws IOException {
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    int letter;
    while ((letter = stream.read()) != -1)
        baos.write(letter);

    return new String(baos.toByteArray());
}

2) Then create a specific deserializer derialize the object from json. 'NewImage' in case of DynamoDB event. One example here.

Answer 5

Create a handler that takes an InputStream, read in the contents of the InputStream (which is just JSON) and then deserialize it to get the data that you need.

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import com.amazonaws.services.lambda.runtime.Context; 

public class MyHandler {    
    public void handler(InputStream inputStream, OutputStream outputStream, Context context) throws IOException {           
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int letter;        
        while((letter = inputStream.read()) != -1)
        {
            baos.write(letter);                     
        }        

        //Send the contents of baos to a JSON deserializer ...          
    }      
}

It's a bit cumbersome, but as far as I'm aware AWS doesn't currently provide a higher level Java lambda interface for consuming DynamoDB Streams. I have a full blown example here with details on how I deserialized the stream of JSON to get Java objects for the data.