Spring（4.2.6）+ Jackson（2.8.4）+泛型类型：java.util.LinkedHashMap无法转换为

Question

After two days, I'm stuck with the following...

If I specify the type in the controller, it works:

@RestController
public class FooController {
    @RequestMapping(method = RequestMethod.POST)
    protected ResponseModel bar(@Valid @RequestBody Foo foo) {
        // here I have foo of type Foo
    }
}

However, if I try to take advantage of generics, it doesn't work:

public class Base<U> {
    @RequestMapping(method = RequestMethod.POST)
    protected ResponseModel bar(@Valid @RequestBody U entity) {
        // here I get java.util.LinkedHashMap instead of U
        // which, in the FooController, should be Foo
    }
}

@RestController
public class FooController extends Base<Foo> {
}

Looking at the logs, when it hits the controller with defined type I get:

Read [class com...Foo] as "application/json;charset=UTF-8" with [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter@cee662]

While at the generic one:

Read [U] as "application/json;charset=UTF-8" with [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter@cee662]

Q: What should I do to take advantage of the Generic Type, and to be able to cut the repeated code from the controllers?

Note: this is NOT a duplicate, since all the other questions are about List<T> or from an issue on ~2.6.*

Addendum: Yuri-M-Dias suggested downgrading, which I did, so 2.5.5 works with a Generic Type, but 2.8.4 doesn't. (At least for now I have a bad and good revision to work with...)

Going further into the downgrade...

I found out that the revision 2.7.9 is a good one, I get Foo out of U , while on the 2.8.0 I get the LinkedHashMap<K,V> ... maybe I missed something from the 2.8.0 release ?

Answer 1

I don't know if you happened to see Generic Controller in Spring MVC , but it may be instructive. Still, I'm not happy with what I'm about to describe, because I see what you're trying to do above. Additionally, I can't give you the reason behind the possible "necessity." Hopefully someone else will be able to fill that it.

@RestController
public class FooController extends Base<Foo> {
    @RequestMapping(method = RequestMethod.POST)
    protected ResponseModel bar(@Valid @RequestBody Foo foo) {
        super.bar(foo);
    }
}

Seems like that should make everything happy.