Cannot deserialize java.time.Instant - jackson

Question

I have a RestEasyClient that has to deserialize an object that has a java.time.Instant inside. I tried to register the new JavaTimeModule from jsr310 but still got errors:
ObjectMapper mapper = new ObjectMapper()
.registerModule(new JavaTimeModule());
ResteasyClient client = new ResteasyClientBuilder()
.register(mapper)
.build();
ResteasyWebTarget target = client.target(UriBuilder.fromPath(SERVICE_URL + "/api"));
Error:
Can not construct instance of java.time.Instant: no suitable constructor found, can not deserialize from Object value (missing default constructor or creator, or perhaps need to add/enable type information?)
After modifying Rest Server to properly serialize the Instant class (ex: "fromTime": 1525681860)
New Error:
Can not construct instance of java.time.Instant: no double/Double-argument constructor/factory method to deserialize from Number value (1.52568186E9)
I managed to simulate this:
ObjectMapper deserializer = new ObjectMapper()
.registerModule(new JavaTimeModule());
Instant probe = deserializer.readValue("1525681860", Instant.class);
System.out.println(probe);
If I remove the "registerModule" line, I get the same error.
Therefore, the conclusion is that RestEasyClient not registering the module. I am definitely doing something wrong.

Answer 1

You could define a ContextResolver for ObjectMapper:
public class ObjectMapperContextResolver implements ContextResolver<ObjectMapper> {
private final ObjectMapper mapper;
public ObjectMapperContextResolver() {
this.mapper = createObjectMapper();
}
#Override
public ObjectMapper getContext(Class<?> type) {
return mapper;
}
private ObjectMapper createObjectMapper() {
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());
mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
return mapper;
}
}
And then register the resolver in your client instance:
ResteasyClient client = new ResteasyClientBuilder()
.register(ObjectMapperContextResolver.class).build();
Alternatively you could register an instance of JacksonJsonProvider. This class is the basic implementation of JAX-RS abstractions (MessageBodyReader and MessageBodyWriter) needed for binding JSON content to and from Java objects.
You can use the constructor that accepts an ObjectMapper instance.