spring-projects / spring-projects/spring-framework

Resolving generic enum types (Enum<T>) in nested bean properties

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in: core status: feedback-provided type: enhancement
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Java
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Description

Affects: 5.3.10

I am experiencing a problem with MVC method argument resolving in GET invocations. I have already reduced my problem to a bunch of classes and a reproducible example using Spring Test.

The idea is that I have a Filter Framework that heavily relies on generics. The first part of the FF, the one we are dealing with, is MVC argument resolution. The second part is translation into ORM predicates, which is out of scope.

@Data
public class SimpleFilter<T> {

    /**
     * Requires the property to be equal to the value
     */
    protected T eq;
    /**
     * Requires the property to be different from the value
     */
    protected T ne;
    /**
     * Requires the property to be any of the supplied values
     */
    protected T[] in;
    /**
     * Requires the property not to be any of the supplied values
     */
    protected T[] notIn;

    /**
     * Requires the property to be either not null or null.
     * The property can be used as:
     * <p>
     * - Unspecified: null check is ignored
     * - True: the property must be null
     * - False: the property must be not null
     */
    protected Boolean isNull;

}

Let's not talk about IntegerFilter and LongFilter, let's focus on a generic EnumFilter

public class EnumFilter<T extends Enum<T>> extends SimpleFilter<T> {
}

I know that Java erases generic types to the lower bound (java.lang.Enum), but the generic information is preserved in Java 11 when applied to a field.

Consider this particular filter

@Data
public class ExampleTestFilter implements Filter {


    private AmlObjectTypeFilter exampleObjectTypeEnum;

    private EnumFilter<AmlObjectType> exampleObjectTypeEnumGeneric;

    private SimpleFilter<AmlObjectType> exampleObjectTypeSimple;

    public static class AmlObjectTypeFilter extends SimpleFilter<AmlObjectType> {

    }
}

Consider the following controller:

@RestController
@RequestMapping("/exampleFiltering")
@Data
public class FilteringArgumentResolverTestController {

    private ExampleTestFilter filter;

    /**
     * Sample no-op function
     */
    @GetMapping
    @ResponseStatus(HttpStatus.NO_CONTENT)
    public void handleExampleTestFilter(@ModelAttribute("filter") ExampleTestFilter filter) {
        this.filter = filter;
    }
}

Now consider the following tests

@SpringBootTest(classes = AmlControlliBeApplication.class)
@ComponentScan(basePackageClasses = FilterArgumentResolverWeb2Test.class)
class FilterArgumentResolverWeb2Test extends AbstractOrbitE2eTest {

    private final FilteringArgumentResolverTestController controller;

    @Autowired
    FilterArgumentResolverWeb2Test(ConfigurableApplicationContext applicationContext, PlatformTransactionManager transactionManager, DataSource dataSource, MockMvc mockMvc, ObjectMapper objectMapper, FilteringArgumentResolverTestController controller) {
        super(applicationContext, transactionManager, dataSource, mockMvc, objectMapper);
        this.controller = controller;
    }


    @Test
    void resolveArgument_amlObjectTypeEnum_ok() {
        String value = "CONTROL";

        assertDoesNotThrow(() -> getMockMvc().perform(get("/exampleFiltering")
                        .queryParam("exampleObjectTypeEnum.eq", value))
                .andExpect(status().isNoContent())
        );

        assertAll(
                () -> assertThat(controller.getFilter(), is(notNullValue())),
                () -> assertThat(controller.getFilter(), is(instanceOf(ExampleTestFilter.class))),
                () -> assertThat(controller.getFilter(), hasProperty("exampleObjectTypeEnum", is(notNullValue()))),
                () -> assertThat(controller.getFilter(), hasProperty("exampleObjectTypeEnum", hasProperty("eq", equalTo(AmlObjectType.CONTROL))))
        );
    }

    @Test
    void resolveArgument_amlObjectTypeSimple_ok() {
        String value = "CONTROL";

        assertDoesNotThrow(() -> getMockMvc().perform(get("/exampleFiltering")
                        .queryParam("exampleObjectTypeSimple.eq", value))
                .andExpect(status().isNoContent())
        );
        assertAll(
                () -> assertThat(controller.getFilter(), is(notNullValue())),
                () -> assertThat(controller.getFilter(), is(instanceOf(ExampleTestFilter.class))),
                () -> assertThat(controller.getFilter(), hasProperty("exampleObjectTypeSimple", is(notNullValue()))),
                () -> assertThat(controller.getFilter(), hasProperty("exampleObjectTypeSimple", hasProperty("eq", equalTo(AmlObjectType.CONTROL))))
        );
    }
}

The problems here

If I declare (even as a static class) a boilerplate filter class bound to the AmlObjectType enum, it works. But if I declare a field as EnumFilter<AmlObjectType> Spring is unable to resolve the property as it thinks the property value should be cast to Enum, which is the generic bound of EnumFilter<T extends Enum<T>>.

E.g. using GET /api?exampleObjectTypeEnum.eq=CONTROL works, using GET /api?exampleObjectTypeEnumGeneric.eq=CONTROL or GET /api?exampleObjectTypeSimple.eq=CONTROL does not.

It would not happen using JSON POST with Jackson Object Mapper.

  assertDoesNotThrow(() -> getMockMvc().perform(get("/exampleFiltering")
                        .queryParam("exampleObjectTypeSimple.eq", value))
                .andExpect(status().isNoContent())
        );

Caused by: java.lang.AssertionError: 
Expected: hasProperty("exampleObjectTypeSimple", hasProperty("eq", <CONTROL>))
     but:  property 'exampleObjectTypeSimple'  property 'eq' was "CONTROL"
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
	at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:6)
	at it.orbit.common.web.filtering.FilterArgumentResolverWeb2Test.lambda$resolveArgument_amlObjectTypeSimple_ok$44(FilterArgumentResolverWeb2Test.java:195)
	at org.junit.jupiter.api.AssertAll.lambda$assertAll$1(AssertAll.java:68)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)
	at java.base/java.util.stream.ReferencePipeline$11$1.accept(ReferencePipeline.java:442)
	at java.base/java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)
	at org.junit.jupiter.api.AssertAll.assertAll(AssertAll.java:77)
	... 87 more

In this case, using SimpleFilter<AmlObjectType> results in Spring setting the value CONTROL (String) as an Object into the property, which fails the assertion because I am comparing an enum with a string.

  assertDoesNotThrow(() -> getMockMvc().perform(get("/exampleFiltering")
                        .queryParam("exampleObjectTypeEnumGeneric.eq", value))
                .andExpect(status().isNoContent())
        );

2021-12-02 16:40:48.514 DEBUG 2248 --- [    Test worker] o.s.t.web.servlet.TestDispatcherServlet  : GET "/exampleFiltering?exampleObjectTypeEnumGeneric.eq=CONTROL", parameters={masked}
2021-12-02 16:40:48.520  WARN 2248 --- [    Test worker] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.validation.BindException: org.springframework.validation.BeanPropertyBindingResult: 1 errors
Field error in object 'filter' on field 'exampleObjectTypeEnumGeneric.eq': rejected value [CONTROL]; codes [typeMismatch.filter.exampleObjectTypeEnumGeneric.eq,typeMismatch.exampleObjectTypeEnumGeneric.eq,typeMismatch.eq,typeMismatch.java.lang.Enum,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [filter.exampleObjectTypeEnumGeneric.eq,exampleObjectTypeEnumGeneric.eq]; arguments []; default message [exampleObjectTypeEnumGeneric.eq]]; default message [Failed to convert property value of type 'java.lang.String' to required type 'java.lang.Enum' for property 'exampleObjectTypeEnumGeneric.eq'; nested exception is java.lang.IllegalArgumentException: The target type java.lang.Enum does not refer to an enum]]

In this case, Spring detects the target type as Enum, and can't cast CONTROL to the root Enum class

  assertDoesNotThrow(() -> getMockMvc().perform(get("/exampleFiltering")
                        .queryParam("exampleObjectTypeEnum.eq", value))
                .andExpect(status().isNoContent())
        );

This succeeds because target property is of type AmlObjectTypeFilter which is bound directly to AmlObjectType

Debugging

org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessException details (1) are:
PropertyAccessException 1:
org.springframework.beans.TypeMismatchException: Failed to convert property value of type 'java.lang.String' to required type 'java.lang.Enum' for property 'exampleObjectTypeEnumGeneric.eq'; nested exception is java.lang.IllegalArgumentException: The target type java.lang.Enum does not refer to an enum
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertIfNecessary(AbstractNestablePropertyAccessor.java:600)
	at org.springframework.beans.AbstractNestablePropertyAccessor.convertForProperty(AbstractNestablePropertyAccessor.java:609)
	at org.springframework.beans.AbstractNestablePropertyAccessor.processLocalProperty(AbstractNestablePropertyAccessor.java:458)
	at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:278)
	at org.springframework.beans.AbstractNestablePropertyAccessor.setPropertyValue(AbstractNestablePropertyAccessor.java:266)
	at org.springframework.beans.AbstractPropertyAccessor.setPropertyValues(AbstractPropertyAccessor.java:104)
	at org.springframework.validation.DataBinder.applyPropertyValues(DataBinder.java:851)
	at org.springframework.validation.DataBinder.doBind(DataBinder.java:747)
	at org.springframework.web.bind.WebDataBinder.doBind(WebDataBinder.java:198)
	at org.springframework.web.bind.ServletRequestDataBinder.bind(ServletRequestDataBinder.java:118)
	at org.springframework.web.servlet.mvc.method.annotation.ServletModelAttributeMethodProcessor.bindRequestParameters(ServletModelAttributeMethodProcessor.java:158)
	at org.springframework.web.method.annotation.ModelAttributeMethodProcessor.resolveArgument(ModelAttributeMethodProcessor.java:171)
	at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121)
	at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:179)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:146)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:655)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
	at org.springframework.test.web.servlet.TestDispatcherServlet.service(TestDispatcherServlet.java:72)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
	at org.springframework.mock.web.MockFilterChain$ServletFilterProxy.doFilter(MockFilterChain.java:167)
	at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:134)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:327)
	at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:115)
	at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:81)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:121)
	at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:115)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:105)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:149)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:63)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.oauth2.server.resource.web.BearerTokenAuthenticationFilter.doFilterInternal(BearerTokenAuthenticationFilter.java:121)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:103)
	at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:89)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.header.HeaderWriterFilter.doHeadersAfter(HeaderWriterFilter.java:90)
	at org.springframework.security.web.header.HeaderWriterFilter.doFilterInternal(HeaderWriterFilter.java:75)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:110)
	at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:80)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.context.request.async.WebAsyncManagerIntegrationFilter.doFilterInternal(WebAsyncManagerIntegrationFilter.java:55)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:336)
	at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:211)
	at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183)
	at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358)
	at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271)
	at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:134)
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
	at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:134)
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
	at org.springframew

I also found that Spring could be aware of the actual generic type of a field at some point. I was spelunking deep into Introspector and found the below

Screenshot debugging

This shows that the generic type is known for the field, but then looks like Spring ignores the property generic binding and works only on the (raw....) type.

At AbstractNestablePropertyAccessors# variable ph has now lost any information about the generic binding of the filter class's property.

And at line 590 the "target class" is now just Enum.

Porkarounds

  • Use HTTP POST to deserialize the filter object
  • Define a subclass for each Enum you want to use in a filter

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the MockMvc cases in FilterArgumentResolverWeb2Test.java, especially the nested generic enum properties. Start with AbstractNestablePropertyAccessor.convertIfNecessary and the ModelAttributeMethodProcessor path shown in the trace. Done means generic nested properties resolve AmlObjectType.CONTROL rather than retaining a String or treating the target as java.lang.Enum.

Written by the indexing model from the issue text.

Assessment

Tech stack
java, spring
Domain
api, backend
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
55/100

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