Referencing changelogs from S3

I am building a lambda function in AWS that uses the Java API. Essentially, I want the lambda to pull the changelogs / artifacts from S3. Has anyone done anything similar?

The structure in S3 is something like:

s3Bucket/db/dbName/changelog.xml
s3Bucket/db/dbName/changelogs/changelog2.sql

s3Bucket/db/dbName/changelogs/changelogN.sql

In the Java call, how would I pass the S3 changelog key to the constructor:
String changelog = “how to pass the S3 object key?”
ResourceAccessor = which resource accessor will handle this?
Liquibase liquibase = new Liquibase(changelog, resourceAccessor, database);

Thank you.