David A Good

Basics of Using DynamoDB with Java

December 01, 2020

WIP: open questions, lessons learned, tips, etc. from working with DynamoDB in Java.

Different SDKs

Below are the official SDKs and clients available for Java. Beware of different SDKs especially when researching issues, e.g. before digging into documentation, check which SDK or which version it is for.

Watch out for transactional operations as well. They have their own classes, like Get and Put

Just as with Java, NodeJS and Python have older, lower-level SDKs which require you to write DynamoDB JSON, like {'Name': {'S': 'Jack}}, and newer SDKs which take care of the datatype “wrapping” for you so you can just write: {'Name': 'Jack'}

AWS SDK v2 Java

Feature Requests



Questions and Answers

How is UpdateItem handled if no existing item matches the supplied Key?

Answer: A new item is created with the supplied key and the update supplied in the UpdateExpression.


Start with an empty table

PK SK UserName

…and run this:

aws dynamodb --table MyTable --key '{"PK": {"S": "ORDER#123"}, "SK": {"S": "A"}}' --update-expression "set UserName = :username" --expression-attribute-values = '{":username": {"S": "User123"}}'

This will result in a new item being created:

PK SK UserName
ORDER#123 A User123

To prevent this you must add a ConditionExpression which will result in a condition check failure if no item matches the provided Key (and therefore no PK attribute exists for that Key):

--condition-expression "attribute_exists(PK)"

Software engineer crafting full-stack, cloud-native solutions for enterprise. GitHub | LinkedIn | Twitter