Generics with Spring RESTTemplate

I have a class like that:

public class Wrapper<T> {

 private String message;
 private T data;

 public String getMessage() {
    return message;
 }

 public void setMessage(String message) {
    this.message = message;
 }
 
 public T getData() {
    return data;
 }

 public void setData(T data) {
    this.data = data;
 }

}

and I use resttemplate as follows:

...
Wrapper<Model> response = restTemplate.getForObject(URL, Wrapper.class, myMap);
Model model = response.getData();
...

However it throws a:

ClassCastException

I read that: https://stackoverflow.com/questions/4392326/problem-when-trying-to-use-jackson-in-java but didn't help. There are some topics related to my problem etc.: https://jira.springsource.org/browse/SPR-7002 and https://jira.springsource.org/browse/SPR-7023

Any ideas?

PS: My error is that:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to a.b.c.d.Model

I think resttemplate can not understand my generic variable and maybe it accepts it as an Object instead of generic T. So it becomes a LinkedHashMap. You can read from it here It says that when explaining from what it marshalls to:

> JSON Type | Java Type > > object | LinkedHashMap

ParameterizedTypeReference has been introduced in 3.2 M2 to workaround this issue.

Wrapper<Model> response = restClient.exchange(loginUrl, 
                          HttpMethod.GET, 
                          null, 
                          new ParameterizedTypeReference<Wrapper<Model>>() {}).getBody();

However, the postForObject/getForObject variant was not introduced.

The only thing I think you could do is creating a new class that extends Wrapper and uses model as a generic.

class WrapperWithModel extends Wrapper<Model>{};

WrapperWithModel response = restTemplate.getForObject(URL, WrapperWithModel.class);

It's not the best solution, but at least you won't have to unmarshall manually the response.

Do not use generics with RestTemplate. Wrap request and response object with wrapper object that will hide the generics.