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Bug: JSON serialization ignores fields from child classes (Java 8 Lambda runtime works, Java 11 Lambda runtime fails) #358
Description
I noticed this issue when updating my lambda function from Java 8 to Java 11, and it seems to be related to the code in this repository.
The problematic situation occurs when a lambda function declares that it returns TestParent, but actually returns an instance of TestChild:
public class TestParent {
public String parentField = "parentField";
}
public class TestChild extends TestParent {
public String childField = "childField";
}To reproduce the issue, please run the attached test case (maven project): aws-lambda-json-child-field-bug.zip
It should fail with an error like below:
org.junit.ComparisonFailure:
Expected :{"parentField":"parentField","childField":"childField"}
Actual :{"parentField":"parentField"}
You can see that the fields from TestChild are missing. This is the issue, and this seems to be new -- in the Java 8 lambda runtime this worked ok.
Thanks for any help!
Activity
msailes commentedon Jul 28, 2022
Hi @Dretch,
I tried your sample and I couldn't get it to pass with Java 8. Could you provide a sample which is passing.
Thanks,
Dretch commentedon Jul 28, 2022
Thanks for looking @msailes
The issue does not seem to be Java 8 vs Java 11 per-se, but rather the Java 8 lambda runtime vs the Java 11 lambda runtime. So I am not expecting the test to pass simply using a Java 8 JRE.
I'm not sure if the code in this library even existed in the Java 8 lambda runtime, but nevertheless the code in this library does behave differently to the equivalent code in the Java 8 runtime.
Dretch commentedon Aug 5, 2022
I have created a proof-of-concept that shows how the Java 8 runtime works but the Java 11 runtime does not: https://github.com/Dretch/java-11-lambda-missing-fields-poc (see project README).
Hopefully this helps to investigate the issue.
msailes commentedon Aug 12, 2022
Hi @Dretch,
You are correct, there is a difference between the two versions in this case. The fix would be to use the child type instead.
Thanks.
Dretch commentedon Aug 12, 2022
Hi @msailes ,
Unfortunately in my real application there is more than one child type, and which type will be used is not known until runtime - so it is not possible to statically declare the child type.
maxday commentedon Aug 6, 2025
hi @Dretch
Following up (super late) on this, are you still facing the issue?
Thanks