Cannot Select Parameterized Type
I Want to Create a Rest to Communicate Between Server and Client. the Constructor Given Below: Public Class Resthelper { Public Resthelper(String Url, I Input...
I want to create a rest to communicate between server and client.
The constructor given below:
public class RestHelper<I, R> {
public RestHelper(String url, I input, Class<R> output){
ResponseEntity<R> responseEntity = restTemplate.exchange(url, HttpMethod.POST, requestEntity, output );
}
}
For normal type, I can do:
RestHelper<User, Result> helper = new RestHelper<>(url, user, Result.class);
How can I pass a generic type, like:
ResultContainData<Boolean>
The code below is not working:
ResultContainData<Boolean> result = new ResultContainData<>();
RestHelper<User, ResultContainData<Boolean>> helper = new RestHelper<>(url, user, (Class<ResultContainData<Boolean>>) ((ParameterizedType) result.getClass().getGenericSuperclass()).getActualTypeArguments()[0]);
I got a runtime error: cannot cast to ParameterizedType.
2 Answers
I got the solution.
ResultContainData<Boolean> result = new ResultContainData<>();
RestHelper<User, ResultContainData<Boolean>> helper = new RestHelper<>(url, user, (Class<ResultContainData<Boolean>>)result.getClass());
It's working for me. I am still looking for a better solution.
You can only learn the value of I and R by capturing them in a subclass definition - otherwise they are erased at runtime. Ex:
class MyStringRestHelper extends RestHelper<String, String> {
Then using something like my TypeTools you can resolve the values of I and R:
Class<?>[] typeArgs = TypeResolver.resolveRawArguments(RestHelper.class, MyStringRestHelper.class);
Class<?> i = typeArgs[0];
Class<?> r = typeArgs[1];
assert i == r == String.class;
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
