带有 SNS 的 Lambda -> SQS AWS

Question

Im have a aws lambda which will be triggered from SNS -> SQS. It means, I have a SNS and then SQS is a subcriber. Then I have a lambda triggered by SQS.

I have build a simple Lambda as below

public class EnhancedCanonicalLambdaHandler implements RequestHandler<SQSEvent, String> {
    static final Logger log = LogManager.getLogger(EnhancedCanonicalLambdaHandler.class);
    static final ObjectMapper objectMapper = new ObjectMapper();

    @Override
    public String handleRequest(SQSEvent sqsEvent, Context context) {
        log.info("There are {} records to be processing ...", sqsEvent.getRecords().size());

        for(SQSEvent.SQSMessage msg : sqsEvent.getRecords()) {
// I want to map msg.getBody()
        }
    }

And the msg.getBody will have json like below

{
   "Type":"Notification",
   "MessageId":"d3056919-1db0-5bcb-b5ce-3df0eb234dd9",
   "TopicArn":"arn:aws:sns:us-east-2:enhance-canonical-topic",
   "Subject":"nghia do subject",
   "Message":"{\n\"groupRuleSourceLocation\" : \"groupRuleSourceLocation\",\n\"canonicalSourceLocation\": \"canonicalSourceLocation\"\n}",
   "Timestamp":"2019-02-22T13:08:35.147Z",
   "SignatureVersion":"1",
   "SigningCertURL":"https://sns.us-east-2.amazonaws.com/.pem",
   "UnsubscribeURL":"https://sns.us-east-2.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:us-east-2:057351434671:enhance-canonical-topic:",
   "MessageAttributes":{}
}

I would like to see if AWS they have anyway to map this body message to an Pojo defined already? or we need to use json or mapper to map to an object we define?

Thanks,

Answer 1

You'll have to map it yourself or use mappers (like you mentioned) such as Gson or Jackson

Here's an example of how you can achieve this using Gson:

Gson gson = new Gson();
String snsOrSqsMessageBody = "{\r\n   \"Type\":\"Notification\",\r\n   \"MessageId\":\"d3056919-1db0-5bcb-b5ce-3df0eb234dd9\",\r\n   \"TopicArn\":\"arn:aws:sns:us-east-2:enhance-canonical-topic\",\r\n   \"Subject\":\"nghia do subject\",\r\n   \"Message\":\"{\\n\\\"groupRuleSourceLocation\\\" : \\\"groupRuleSourceLocation\\\",\\n\\\"canonicalSourceLocation\\\": \\\"canonicalSourceLocation\\\"\\n}\",\r\n   \"Timestamp\":\"2019-02-22T13:08:35.147Z\",\r\n   \"SignatureVersion\":\"1\",\r\n   \"SigningCertURL\":\"https:\/\/sns.us-east-2.amazonaws.com\/.pem\",\r\n   \"UnsubscribeURL\":\"https:\/\/sns.us-east-2.amazonaws.com\/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:us-east-2:057351434671:enhance-canonical-topic:\",\r\n   \"MessageAttributes\":{}\r\n}";
MyCustomClass myCustomObject = gson.fromJson(snsOrSqsMessageBody, MyCustomClass.class);

Just for the sake of curiosity: what role is SQS playing in your application? You could simply subscribe your Lambda to your SNS topic, removing one layer of complexicity in your architecture.

Hope this helps!