Java/spring reflection, fill object instance dynamically from Strings

I have a Map as followed:

final Map<String, String[]> paramMap = multipartRequest.getParameterMap();

and im filling the values using reflections into a model:

final Class<?> requestClass = config.getModelClazz();
        Object requestModel = new Object();
        try {
            requestModel = requestClass.newInstance();
        } catch (InstantiationException | IllegalAccessException e1) {
            LOGGER.warn("Failed while creating instance: " + e1);
        }

        for (final Field field : requestClass.getDeclaredFields()) {
            field.setAccessible(true);
            for (final Map.Entry<String, String[]> entry : paramMap.entrySet()) {
                if (field.getName().equals(entry.getKey())) {
                    try {
                        field.set(requestModel, entry.getValue()[0]);
                    } catch (IllegalArgumentException | IllegalAccessException e1) {
                        LOGGER.warn("Failed while setting value: " + e1);
                    }
                }
            }
        }

The problem is that field.set() can only set values from the model which are strings, since the value-entry of the map is a string too. I know that spring somehow can convert request-params in primitive types. For example:

if you call the url /test.view?age=18&isMale=true and have a GET-Controller as followed:

 @RequestMapping(value = "/test.view", method = RequestMethod.GET)
public String openView(@ModelAttribute(value = "test") final Test test){

    return "test";
}

public class Test {
   private Integer age;
   private Boolean isMale;
   //getter & setter
}

the request-params are getting filled into the model, which are not only Strings

Does anyone know, how exacly they are mapping the request-params to other types? Or do you have any different approach for my problem?