ServerWebInputException is throw each time Http request with mandatory request parameters is handled. [SPR-17338]

[spring-projects-issues]

Dmytro Mrachkovskyi opened SPR-17338 and commented

ServerWebInputException is throw each time Http request with mandatory request parameters is handled in AbstractNamedValueArgumentResolver. Even though this does not brake request handling flow, exception (and stack trace)  is generated each time and it has performance impact. 

Root-cause: 

In

 

org.springframework.web.reactive.result.method.annotation.AbstractNamedValueArgumentResolver#resolveArgument 

 return this.resolveName(resolvedName.toString(), nestedParameter, exchange)
.flatMap((arg) -> mappingFunction())
.switchIfEmpty(this.getDefaultValue(namedValueInfo, parameter, bindingContext, model, exchange));

switchIfEmpty takes default value as an argument. As for mandatory arguments there is no default value ServerWebInputException will be thrown in getDefaultValue() method and wrapped into Mono.error(ex). This error mono will never be used until mandatory request parameter exists, but Exception it self is crated when there is no need in it.

Fix. Default value should be evaluated only if request parameter is empty: 

package org.springframework.web.reactive.result.method.annotation;

public abstract class AbstractNamedValueArgumentResolver extends HandlerMethodArgumentResolverSupport {

...

private Mono<Object> getDefaultValue(NamedValueInfo namedValueInfo, MethodParameter parameter,
        BindingContext bindingContext, Model model, ServerWebExchange exchange) {
        return Mono.fromSupplier(() -> {
            Object value = null;
            if (namedValueInfo.defaultValue != null) {
                value = resolveStringValue(namedValueInfo.defaultValue);
            }
            else if (namedValueInfo.required && !parameter.isOptional()) {
                handleMissingValue(namedValueInfo.name, parameter, exchange);
            }
            value = handleNullValue(namedValueInfo.name, value, parameter.getNestedParameterType());
            value = applyConversion(value, namedValueInfo, parameter, bindingContext, exchange);
            handleResolvedValue(value, namedValueInfo.name, parameter, model, exchange);
            return value;
        });
}

---

Affects: 5.0.9, 5.1 GA

Referenced from: commits 983bce1, 8422976

Backported to: 5.0.10

[spring-projects-issues]

Dmytro Mrachkovskyi commented

Pull request

[spring-projects-issues]

Rossen Stoyanchev commented

Indeed this is eagerly creating an Exception instance only to supply a default value that might not be needed in the end.