RestTemplate fails to convert properly for Generic Type Container with MappingJacksonHttpMessageConverter [SPR-7002]

[spring-projects-issues]

Simon Wong opened SPR-7002 and commented

When I used RestTemplate to retrieve the result in Generic Type Container, the MappingJacksonHttpMessageConverter could not properly determine the type (due to erasure)

e.g.

List<MyDomain> myDomainList = restTemplate.getForObject(uri, List.class);
will throw ClassCastException

the MappingJacksonHttpMessageConverter could not determine that the List container should stores MyDomain objects by passing the List.class, it could only stores as List<LinkedHashedMap>

Recommend to add something similar to TypeReference in Jackson. http://wiki.fasterxml.com/JacksonInFiveMinutes (Section: Data Binding with Generics) to solve this issue.

Personal speaking, if the new HttpEntity could provide a setTypeReference() would be much convenient.
e.g.
HttpEntity httpEntity = new HttpEntity();
httpEntity.setTypeReference(new TypeReference<List<MyDomain>>() {});

List<MyDomain> myDomainList = restTemplate.getForObject(uri, httpEntity);

---

Affects: 3.0 GA, 3.0.1

Issue Links:

• #11685 Proper handling of parameterized types in RestTemplate

Referenced from: commits a1f6eab, 247c46e, 212daa1

0 votes, 7 watchers

[spring-projects-issues]

Arjen Poutsma commented

I'm not sure I understand the second part of the description. HttpEnity is not (designed to be) used as a argument for getForObject. HttpEntity either represents request/response entity that is to be posted/retrieved, it cannot be used in the above manner.

[spring-projects-issues]

Arjen Poutsma commented

Introducing the TypeReference concept is to big a change for a minor version. I've created #11685 (scheduled for 3.1) for that.

For the time being, I've introduced a simple workaround. There is now a getJavaType method, which you can override to customize the JavaType Jackson serializes to. For instance:

converter = new MappingJacksonHttpMessageConverter() {
	@Override
	protected JavaType getJavaType(Class<?> clazz) {
		if (List.class.isAssignableFrom(clazz)) {
			return TypeFactory.collectionType(ArrayList.class, MyBean.class);
		}
		else {
			return super.getJavaType(clazz);
		}
	}
};

This will have to do for now, before we properly tackle this in 3.1.

[spring-projects-issues]

Simon Wong commented

I guess I really misunderstand the response entity before (just treat it as the meta-data for the HTTP resources). It has been clarified after read the JIRA #11634 carefully.

Thanks for your help.

[spring-projects-issues]

Ioannis Foukarakis commented

A little bit late comment, but another workaround is to use
MyDomain[] myDomains = restTemplate.getForObject(uri, MyDomain[].class);

then convert the array to a list (if needed).
I had a similar issue, tested it with Spring 3.0.2 and it worked.

Also tried to use (new ArrayList<MyDomain>()).getClass(), but it returned ArrayList as a type and it failed (as expected).

[spring-projects-issues]

Simon Wong commented

Thanks. But Array is reified (according to Java Language Spec 4.7), which will lost type safety