`Unpaged` instances not Jackson-serializable out of the box

[Nowheresly]

Hi,

after upgrading to spring boot 3.2.0, some unit tests failed with the error:

16:10:11.695 [main] INFO org.springframework.mock.web.MockServletContext -- Initializing Spring TestDispatcherServlet ''
16:10:11.695 [main] INFO org.springframework.test.web.servlet.TestDispatcherServlet -- Initializing Servlet ''
16:10:11.695 [main] INFO org.springframework.test.web.servlet.TestDispatcherServlet -- Completed initialization in 0 ms
16:10:11.701 [main] WARN org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver -- Resolved [org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.UnsupportedOperationException)]

java.lang.AssertionError: Status expected:<200> but was:<500>
Expected :200
Actual   :500

Here is the test:

    @Test
    void findAll() throws Exception {
        doReturn(Page.empty()).when(activityLogService).findAll(any(Predicate.class),any(Pageable.class),any());
        mockMvc.perform(get("/api/v1/activity-logs"))
                .andExpect(status().isOk())
                .andReturn();
    }

If I replace

doReturn(Page.empty()).when(activityLogService).findAll(any(Predicate.class),any(Pageable.class),any());
with
doReturn(Page.empty(PageRequest.of(1, 10, Sort.by("id")))).when(activityLogService).findAll(any(Predicate.class),any(Pageable.class),any());
the error is gone.

It seems Page.empty() is not serializable while Page.empty(PageRequest.of(1, 10, Sort.by("id"))) is.

Is it a regression or did I miss something ?

[jsadeli]

similar issue, my error message is:

(was java.lang.UnsupportedOperationException) (through reference chain: org.springframework.data.domain.PageImpl[\"pageable\"]->org.springframework.data.domain.Unpaged[\"offset\"])

[smyth90]

You can return a PagedModel<EntityModel<MyEntity>> instead of Page<MyEntity>:

@Autowired
private final PagedResourcesAssembler<MyEntity> assembler;

public ResponseEntity<PagedModel<EntityModel<MyEntity>>> getEntities(
@RequestParam(value = "page", defaultValue = "0") final int page, 
@RequestParam(value = "size", defaultValue = "2000") final int size) {
			final var pageable = PageRequest.of(page, size);
			final var entities = repository.findAll(pageable);
			// Convert to PagedModel and return it
			return new ResponseEntity<>(assembler.toModel(entities), OK);
}

[Carla-de-Beer]

I have the same issue. All of my mockMvc tests are affected where Page results are returned.

Caused by: org.springframework.http.converter.HttpMessageNotWritableException: Could not write JSON: (was java.lang.UnsupportedOperationException)
	at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:492)
	at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:114)
	at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:297)
	at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:190)
	at 
```org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:78)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:136)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:917)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:829)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
	... 12 more
Caused by: com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.UnsupportedOperationException) (through reference chain: org.springframework.data.domain.PageImpl["pageable"]->org.springframework.data.domain.Unpaged["offset"])

[mp911de]

Our domain objects such as Pageable were never intended to be Jackson-serializable, see #1683

[wutzebaer]

Explaination why this fails: If you instanciate PageImpl without Pageable it uses the "Unpaged" isnatnce.
Before it was an enum, even when it implemented getOffset with "UnsupportedOperationException" it was not called because enums just got serialized as string:

"pageable" : "INSTANCE",

Now unpaged is an Object, and jackson tries to seralize all the fields.

My solution unitl SpringBoot offers a better way to return pages:

Instanciate PageImpl with Pageable as parameter (Of course only in tests):

new PageImpl<>(findAllResult, (Pageable) params.getArgument(1), 1)

[mp911de]

The unpaged object is represented by an enum. As this is an implementation detail, Jackson tends to apply its enum serialization.

[wutzebaer]

In the newest version it is no more an enum

final class Unpaged implements Pageable {

Thats why there errors come up now

[jsadeli]

my workaround to this issue (using custom JsonSerializer component):
https://gist.github.com/jsadeli/3cb5c2d788c853099f24c68709931b50

[claudioaze]

I've solved my tests changing
PageImpl page = new PageImpl<>(myArraylist);

by
Pageable pageable = PageRequest.of(0, 10);
PageImpl page = new PageImpl<>(myArraylist, pageable, myArraylist.size());