Add actuator specific ObjectMapper

[vilhelm-persson-viper]

When using a custom object mapper with MapperFeature.AUTO_DETECT_GETTERS disabled the detailed information for Health endpoint is not returned.

The status is returned as expected but not the detailed information.

From the code the getStatus method has Jackson annotation but the getDetails is lacking annotation.

Problem found using SpringBoot spring-boot-starter-parent version 2.0.1.RELEASE.

As a workaround and for verification of the problem is related to Jackson an MixIn class where created annotation for getStatus and getDetails and after that the information where displayed as expected.

mapper.addMixIn(Health.class, HealthMixIn.class);

public abstract class HealthMixIn {
  @JsonValue public abstract Object getStatus();
  @JsonValue public abstract Object getDetails();
}

How to repeat:

@Bean
@Primary
public ObjectMapper create() {
    ObjectMapper mapper = new ObjectMapper();
    mapper.disable(MapperFeature.AUTO_DETECT_GETTERS)
    return mapper;
}

[philwebb]

I wonder if we should create our own ObjectMapper for the actuator.

[snicoll]

If we do, I am expecting some stuff to be configurable. For instance, you may want that Instant are formatted consistently and having our own means you'd need to configure things in two places. Doing this will certainly break other use cases.

[wilkinsona]

For instance, you may want that Instant are formatted consistently

We document the actuator's format for Instant so I think this is actually an argument in favour of using our own ObjectMapper. Doing so would mean that the precise format of the responses will always match what we've documented.

Doing this will certainly break other use cases

On the other hand, I agree with this. While it may be a bad thing that configuring the global ObjectMapper affects the Actuator's response format, the reality is that it does. I would be surprised if at least some users aren't currently relying on that.

[snicoll]

We document the actuator's format for Instant

I am not surprised but for some reason I completely eluded that. I think it's going to be quite hard to do this right. Users may care about a single ObjectMapper so we should give them the ability to do that. And the auto-configured ObjectMapper is already @Primary so we'd probably need some way to qualify the actuator specific one, if any.

[wilkinsona]

If we add an Actuator-specific ObjectMapper, we'll perhaps be adding to the problem that's described in #1789.

[vilhelm-persson-viper]

Referring to initial title where the problem where detected.

For the Health actuator I think that adding Jackson annotation also for the getDetails method would solve the problem with most custom configuration on the ObjectMapper.