How to pass a generic collection Class object as an argument - spring-mvc

Question

I've RESTful service Spring MVC based.
The service has a RESTful resource method that returns the following response:
public class OperationalDataResponse<T> {
private String status;
private String statusMessage;
private T result;
//getters and setters
}
This response object encapsulates the result object of type T.
On the client side I use RestTemplate with GsonHttpMessageConverter added.
I get the response from service as a ResponseEntity
I handle the generic response with runtime Type as below:
public class OperationalDataRestClient<REQ,RESULT_TYPE> {
public OperationalDataResponse<RESULT_TYPE> getOperationalData(String resourcePath, Map<String, Object> urlVariables, Class<RESULT_TYPE> resultType) {
//code to invoke service and get data goes here
String responseString = responseEntity.getBody();
response = GsonHelper.getInstance().fromJson(responseString, getType(OperationalDataResponse.class, resultType));
}
Type getType(final Class<?> rawClass, final Class<?> parameter) {
return new ParameterizedType() {
#Override
public Type[] getActualTypeArguments() {
return new Type[] { parameter };
}
#Override
public Type getRawType() {
return rawClass;
}
#Override
public Type getOwnerType() {
return null;
}
};
}
}
This works like a charm as long as my resultType is a non-collection class.
So, this works great from caller code:
getOperationalData(someResourcePath, someUrlVariables, MyNonGenericClass.class)
However if my resultType is a collection (say, List<String> or List<MyNonGenericClass>)
then I don't know how to pass the resultType Class from the caller code.
For example, from caller code,
getOperationalData(someResourcePath, someUrlVariables, List.class)
or
getOperationalData(someResourcePath, someUrlVariables, List<MyNonGenericClass>.class)
throws compilation error.
I tried passing on ArrayList.class as well but that too doesn't work.
Any suggestion how can I pass a generic collection as a resultType from caller code (in other words, as an example, how can I pass the class object of a List<String> or List<MyNonGenericClass> from caller code ?)

Answer 1

If you know that ResultType is coming as a List, Then it will obvious fail like you said compilation issue.Why? because you are trying to send a List when you method only accepts a single value.In order to over come that issue you will have to change the method arguments to the following
public OperationalDataResponse<RESULT_TYPE> getOperationalData(String resourcePath, Map<String, Object> urlVariables, List<Class<RESULT_TYPE>> resultType){
....
}
and you will have to make some slight modification to getType() Method,loop it and then pass each class value to getType method like so
for(MyNonGenericClass myClass:mylist){
getType(OperationalDataResponse.class, myClass.getClass());
}