Actuator startup endpoint fails to serialize JSON when field visability is set to 'any'

[iaptekar]

I have a demo project using Spring Boot 2.7.3. The only dependencies are the web and actuator starters. I try to start the application with a BufferingApplicationStartup and set management.endpoints.web.exposure.include=* in application.properties. This goes well and I can access startup metrics at /actuator/startup.

However, if I add the property spring.jackson.visibility.field=any to application.properties and hit the actuator/startup endpoint I get the following error:

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Java 8 date/time type `java.time.Clock$SystemClock` not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable handling (through reference chain: org.springframework.boot.actuate.startup.StartupEndpoint$StartupResponse["timeline"]
->org.springframework.boot.context.metrics.buffering.StartupTimeline["events"]
->java.util.Collections$UnmodifiableRandomAccessList[0]
->org.springframework.boot.context.metrics.buffering.StartupTimeline$TimelineEvent["step"]
->org.springframework.boot.context.metrics.buffering.BufferedStartupStep["recorder"]
->org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup$$Lambda$62/0x0000000800c384d8["arg$1"]
->org.springframework.boot.context.metrics.buffering.BufferingApplicationStartup["clock"])
	at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77) ~[jackson-databind-2.13.3.jar:2.13.3]
	at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1300) ~[jackson-databind-2.13.3.jar:2.13.3]
...

None of the other spring.jackson properties I tried caused this error. Is there perhaps an issue with the ObjectMapper initialization for the startup actuator?

[philwebb]

This is somewhat related to #20291. I'm a little surprised that the same error isn't thrown during regular startup since java.time types are exposed in the getters as well.

@iaptekar Do you have the jackson-datatype-jsr310 library on your classpath? If you're using spring-boot-starter-json or spring-boot-starter-web then it should be pulled in. If not, have you tried adding it to see if it solves the issue?

[iaptekar]

Yes I have jsr310 on the classpath. I am using it via spring-boot-starter-web. Though I have tried adding it as an extra dependency and even had a go at configuring the object mapper in a @Configuration. Nothing changes, as you soon as you add the Visibility.Any option you get that exception.

[wilkinsona]

Jackson's message is misleading. It suggests adding jackson-datatype-jsr310 for any java.time.* type, but jackson-datatype-jsr310 doesn't support serialisation of java.time.Clock$SystemClock. @iaptekar, you may want to raise a Jackson issue for this.

We could address this without tackling #20291 by mapping the StartupTimeline to a DTO where we could have complete control over the classes and their suitability for serialising to JSON. Arguably, this would make the startup endpoint more consistent with other endpoints such as the mappings endpoint and its various descriptors. It would, however, require a breaking change to org.springframework.boot.actuate.startup.StartupEndpoint.StartupResponse which is public API.

[wilkinsona]

We might be able to use @JsonSerialize to take control of how StartupResponse is serialized and avoid the unwanted field serialization.

[philwebb]

I have a branch at https://github.com/philwebb/spring-boot/tree/gh-32297 that shows how @JsonSerialize could work. I'm not totally sure if we should take this approach or not.

[wilkinsona]

I like the approach. It seems low risk and addresses the problem without making a breaking change to public API. One for 3.1.12?