问如何在Spring WebFlux中以编程方式配置请求上下文属性

EN

@Configuration
public class MyDelegatingWebFluxConfiguration extends DelegatingWebFluxConfiguration {
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        registry.freeMarker();
    }
}

freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> request  [in template "index.ftl" at line 8, column 20]

Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??

FTL stack trace ("~" means nesting-related):
- Failed at: ${request.contextPath}  [in template "index.ftl" at line 8, column 18]