Proper handling of parameterized types in RestTemplate [SPR-7023]

[spring-projects-issues]

Arjen Poutsma opened SPR-7023 and commented

Currently, the RestTemplate has no way to handle generic types. In other words, the following does not work:

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

This should be fixed.

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Affects: 3.1.1

Issue Links:

• RestTemplate Converting Generic Types [SPR-8840] #13482 RestTemplate Converting Generic Types ("is duplicated by")
• HttpMessageConverter doesn't support typed collections [SPR-8381] #13028 HttpMessageConverter doesn't support typed collections
• Add PATCH HTTP operation to RestTemplate [SPR-14857] #19423 Add PATCH HTTP operation to RestTemplate
• RestTemplate fails to convert properly for Generic Type Container with MappingJacksonHttpMessageConverter [SPR-7002] #11667 RestTemplate fails to convert properly for Generic Type Container with MappingJacksonHttpMessageConverter

Referenced from: commits ed3823b

14 votes, 16 watchers

[spring-projects-issues]

Fotios Lioutsis commented

I am using version 3.0.3.RELEASE and found that the description above works (since #11667 is resolved). However there is no support for usage of RestTemplate getForObject with a Jackson JavaType instead. Passing responseType object as List.class does not use generics (like List<MyDomain> as response type argument in your example). There should be support as in ObjecMapper method:
public <T> T readValue(Reader src,JavaType valueType)
Perhaps the description should be updated with this in mind.

[spring-projects-issues]

Fotios Lioutsis commented

Clarification to the above comment: it is still failing with ClassCastException unless the workaround of #11667 is used.

[spring-projects-issues]

Jay Xu commented

This scenario exposes the limitation of type-erasing of Java generic handling. Looking forward to solution

[spring-projects-issues]

Mukta commented

Is a fix for this planned in any of the upcoming releases?
Is there a workaround in the time being? Thanks.

[spring-projects-issues]

Rossen Stoyanchev commented

Commit ed3823b045fd19cdb801609eb034c93dd4d75c3f:

This change makes it possible to use the RestTemplate to read an HTTP
response into a target generic type object. The RestTemplate has three
new exchange() methods that accept ParameterizedTypeReference -- a
new class that enables capturing and passing generic type info.
See the Javadoc of the three new methods in RestOperations for a
short example.

To support this feature, the HttpMessageConverter is now extended by
GenericHttpMessageConverter, which adds a method for reading an
HttpInputMessage to a specific generic type. The new interface
is implemented by the MappingJacksonHttpMessageConverter and also by a
new Jaxb2CollectionHttpMessageConverter that can read read a generic
Collection where the generic type is a JAXB type annotated with
@XmlRootElement or @XmlType.