`DefaultAttributeConvererProvider` throws `IndexOutOfBoundException` on `Object` class

DefaultAttributeConvererProvider of dynamodb retrieves its matched types incorrectly. This causes it to create a wrong converter for some generic types.

Describe the bug

The minimal reproduction scenario is:

new DefaultAttributeConverterProvider().converterFor(EnhancedType.of(Object.class));

It generates the following stacktrace:

java.lang.IndexOutOfBoundsException: Index: 0
	at java.util.Collections$EmptyList.get(Collections.java:4456)
	at software.amazon.awssdk.enhanced.dynamodb.DefaultAttributeConverterProvider.createMapConverter(DefaultAttributeConverterProvider.java:179)
	at software.amazon.awssdk.enhanced.dynamodb.DefaultAttributeConverterProvider.findConverter(DefaultAttributeConverterProvider.java:149)
	at software.amazon.awssdk.enhanced.dynamodb.DefaultAttributeConverterProvider.converterFor(DefaultAttributeConverterProvider.java:133)

Possible Solution

I think the code should be:

if (type.rawClass() == Map.class) {

Be aware this not only happens here, but also appears on other places in this class.

The problem is caused because the DefaultAttributeConverterProvider is using the isAssignableFrom call. It writes:

if (type.rawClass().isAssignableFrom(Map.class)) {

Context

Found this while writing with a converer.

Your Environment

• AWS Java SDK version used: latest

[steven-aerts]

Hi, I am perfectly aware of that.

I am just saying that if you use by accident an Object you get the above stack trace due to a bug in the DefaultAttributeConverterProvider. Where its code on a few places says:

if (type.rawClass().isAssignableFrom(Map.class)) {

While it should be:

if (type.rawClass() == Map.class) {

Or even:

if (Map.class.isAssignableFrom(type.rawClass())) {

So the code does not give that strange stacktrace, but hits the correct error message:

.orElseThrow(() -> new IllegalStateException("Converter not found for " + type))

[chrylis]

I just ran across this problem myself. If Object is not supported (annoying but something I can deal with), then trying to map an Object field should produce an error message of “Object is not allowed” rather than a spurious unrelated exception (which, as noted above, results from using an objectively incorrect type conditional in the DefaultAttributeConverterProvider).