Introduce IndexAccessor SPI to customize the SpEL Indexer

[jackmiking]

closes gh-26409.

[jackmiking]

it's glad to hear your response. Your affirmation cheers me up.
I am anticipating the day it is merged into the release version.

[sbrannen]

This has been merged into main in ae3dc0d along with an additional 6 commits that revise the PR.

For an example, see the JacksonArrayNodeIndexAccessor in IndexingTests:

spring-framework/spring-expression/src/test/java/org/springframework/expression/spel/IndexingTests.java

Lines 646 to 687 in ae3dc0d

	/**
	* {@link IndexAccessor} that knows how to read and write indexes in a
	* Jackson {@link ArrayNode}.
	*/
	private static class JacksonArrayNodeIndexAccessor implements IndexAccessor {
	private final ObjectMapper objectMapper;
	JacksonArrayNodeIndexAccessor(ObjectMapper objectMapper) {
	this.objectMapper = objectMapper;
	}
	@Override
	public Class<?>[] getSpecificTargetClasses() {
	return new Class[] { ArrayNode.class };
	}
	@Override
	public boolean canRead(EvaluationContext context, Object target, Object index) {
	return (target instanceof ArrayNode && index instanceof Integer);
	}
	@Override
	public TypedValue read(EvaluationContext context, Object target, Object index) {
	ArrayNode arrayNode = (ArrayNode) target;
	Integer intIndex = (Integer) index;
	return new TypedValue(arrayNode.get(intIndex));
	}
	@Override
	public boolean canWrite(EvaluationContext context, Object target, Object index) {
	return canRead(context, target, index);
	}
	@Override
	public void write(EvaluationContext context, Object target, Object index, @Nullable Object newValue) {
	ArrayNode arrayNode = (ArrayNode) target;
	Integer intIndex = (Integer) index;
	arrayNode.set(intIndex, this.objectMapper.convertValue(newValue, JsonNode.class));
	}
	}
	}

@jackmiking, thanks again for putting together the initial prototype!

@artembilan, @pilak, @jackmiking, @jdomigon, @martin-jamszolik, and anyone else interested, we would be grateful if you could try this out in the upcoming 6.2 M1 release (scheduled for tomorrow) and let us know if you run into any issues or come up with any ideas for how to improve (or simplify) the new IndexAccessor SPI.

Cheers,

Sam

---

p.s. I have opened a separate issue (#32613) to introduce compilation support for an IndexAccessor in Spring Framework 6.2 M2, analogous to the existing CompilablePropertyAccessor SPI and tentatively named CompilableIndexAccessor.

[jackmiking]

I have reviewed the code and made some cases. It works great.

[sbrannen]

Hi @jackmiking,

Thanks for trying it out and letting us know that it works! 👍