HeaderMethodArgumentResolver doesn't resolve Optional.empty() for non-existing header [SPR-15151]

[spring-projects-issues]

Artem Bilan opened SPR-15151 and commented

The test-case to reproduce:

@Test
public void resolveNullHeaderToOptional() throws Exception {
	class Foo {

		public void optionalHeader(@Header("foo") Optional<String> foo) {

		}

	}

	GenericApplicationContext cxt = new GenericApplicationContext();
	cxt.refresh();

	HeaderMethodArgumentResolver resolver = new HeaderMethodArgumentResolver(new DefaultConversionService(),
			cxt.getBeanFactory());


	Method method = ReflectionUtils.findMethod(Foo.class, "optionalHeader", (Class<?>[]) null);
	MethodParameter optionalParameter = new SynthesizingMethodParameter(method, 0);

	Message<String> message = MessageBuilder.withPayload("foo")
//				.setHeader("foo", "bar")
			.build();
	Object result = resolver.resolveArgument(optionalParameter, message);
	assertEquals(Optional.empty(), result);
}

The "guilty" code is here in the AbstractNamedValueMethodArgumentResolver:

if (!ClassUtils.isAssignableValue(parameter.getParameterType(), arg)) {
	arg = this.conversionService.convert(arg, TypeDescriptor.forObject(arg), new TypeDescriptor(parameter));
}

Meanwhile org.springframework.web.method.annotation.AbstractNamedValueMethodArgumentResolver delegates to the ConversionService independently of the types compatibility:

try {
	arg = binder.convertIfNecessary(arg, parameter.getParameterType(), parameter);
}
catch (ConversionNotSupportedException ex) {

The here is like currently Spring Integration relies on the SpEL method invocation and we can't properly move to the InvocableHandlerMethod foundation, because of missing conversions.

I guess I can come up as a workaround with something like OptionalHeaderMethodArgumentResolver implementation, but would be great to have a fix in the Core as well.

Thanks.

---

Affects: 4.3.5

[spring-projects-issues]

Juergen Hoeller commented

I've revised the condition to consider nested parameters as well. So we're still not unconditionally triggering conversion but at least we're always triggering it for Optional now.