Moritz Halbritter's Personal Blog
or: why won’t Micronaut serialize my empty lists?
Micronaut omits fields which are null or empty in its JSON output.
For example, this code
class Dto {
public List<String> foo;
public Optional<String> bar;
public String baz;
}
@Controller
class HelloController {
@Get
public Dto test() {
Dto result = new Dto();
result.foo = Collections.emptyList();
result.bar = Optional.empty();
result.baz = null;
return result;
}
}
results in this JSON:
{}
Micronaut not also omits null fields and empty Optional, but also empty collections. This is a bit surprising.
To disable this behaviour, put this in your application.yml:
jackson:
serialization-inclusion: NON_ABSENT # Omit null and Optional.empty(), but include empty collections
serialization:
indent-output: true # Pretty-print JSON
With this setting, the resulting JSON is
{
"foo" : [ ]
}
If you also want to include null fields and empty Optional, set serializationInclusion to ALWAYS:
{
"foo" : [ ],
"bar" : null,
"baz" : null
}
This behaviour is partly documented here.