Spring Deserializing a date fails with RestClient but passes with WebTestClient

Affects: spring 6.1.0-RC2 with spring boot 3.2.0-RC2 and JDK21

Description I've attached a sample Spring Boot application with a single endpoint that deserializes a date from the request data. The deserialization happens in the following lines of DateDeserializerConfig

module.addDeserializer(LocalDateTime.class, new JsonDeserializer<>() {
    @Override
    public LocalDateTime deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException {
        // the following line returns null when invoked with a RestClient
        String dateTimeWithZone = jsonParser.getValueAsString();
        logger.info("Converting {} to LocalDateTime", dateTimeWithZone);
        return ZonedDateTime.parse(dateTimeWithZone).toLocalDateTime();
    }
});

Steps to Reproduce The application contains 2 integration tests, one of which invokes the endpoint with a RestClient and the other uses WebTestClient. The same request data, headers, etc. are used in both cases.

If the tests in DemoApplicationTests are run, testEndpointWithWebClient passes, but testEndpointWithRestClient fails. The failure is caused by jsonParser.getValueAsString() returning null when the latter test runs.

If the date deserialization logic is removed, both tests pass. demo.zip

Comment From: bclozel

I think this is due to the fact that you're creating your own RestClient instance from a base builder; this means that any Spring Boot auto-configuration is not processed for this instance.

I've changed your test with the following:

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class DemoApplicationTests {

    @Autowired
    private WebTestClient webClient;

    private RestClient restClient;

    @LocalServerPort
    private int port;

    @BeforeEach
    private void setup(@Autowired RestClient.Builder builder) {
        restClient = builder.baseUrl("http://localhost:" + port)
                .defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
                .build();
    }

I think this support has been added in https://github.com/spring-projects/spring-boot/issues/37033

Thanks!

Comment From: donalmurtagh

@bclozel thanks very much for the explanation, I'll give your suggestion a try

Update: it worked!

Comment From: bclozel

Thanks for letting us know @donalmurtagh , and thanks for trying out the RC versions!