Could not write EnvironmentEndpoint bean to JSON (with solution)

[yangzii0920]

Spring-Boot Version: 1.5.9 (issue starts with version 1.5.3)

Description:
I want to get a list of endpoints exposed by actuator.
So I created a bean extending AbstractEndpoin. On invoke it returns a List.
Sample code:

@Component
public cluss LustEndpoints extends AbstractEndpoint<List<Endpoint>>{
private List<Endpoint> endpoints;
@Autowired
public ListEndPoints(List<Endpoint> endpoints) {
	super("showendpoints", false, true);
	this.endpoints = endpoints;
}

@Override
public List<Endpoint> invoke() {
	return this.endpoints;
}
}

After startup and hit the /showendpoints of the server, I got a 500 response and the following message. I changed return object to only the EnvironmentEndpoint to make it clear:

"message": "Could not write JSON document: No serializer found for class org.springframework.core.convert.support.DefaultConversionService and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.springframework.boot.actuate.endpoint.EnvironmentEndpoint["resolver"]->org.springframework.boot.actuate.endpoint.EnvironmentEndpoint$PlaceholderSanitizingPropertyResolver["conversionService"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: No serializer found for class org.springframework.core.convert.support.DefaultConversionService and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: org.springframework.boot.actuate.endpoint.EnvironmentEndpoint["resolver"]->org.springframework.boot.actuate.endpoint.EnvironmentEndpoint$PlaceholderSanitizingPropertyResolver["conversionService"])"

Compare source code of 1.5.2 and 1.5.3, I found difference between invoke() method implementations. I'm not sure if it's a bug or another way to map it.

Solution:
Without changing anything, suggested by the error message, I disabled SerializationFeature.FAIL_ON_EMPTY_BEANS by setting spring.jackson.serialization.FAIL_ON_EMPTY_BEANS=false in properties file.

[bclozel]

This is because in #8282, we introduced a getResolver() method on that class, and Jackson thinks it's a POJO attribute that should be serialized.

Your workaround works, but the bottom line is - you're not supposed to serialize Spring Boot internals as JSON objects - you should at least extract information out of them and use your own DTOs. If you don't, you expose your application to this kind of issue: any change on our side is likely to break your app.