How do we access and respond to CloudFormation custom resources using an AWS Lambda function written in Java?

I have am AWS Lambda function written in Java that I would like to use as part of a response to an AWS CloudFormation function. Amazon provides two detailed examples on how to create a CloudFormation custom resource that returns its value based on an AWS Lambda function written in Node.js, however I have been having difficulty translating the Lambda examples into Java. How can we setup our AWS Java function so that it reads the value of the pre-signed S3 URL passed in as a parameter to the Lambda function from CloudFormation and send back our desired response to the waiting CloudFormation template?