Redirect one Request to many internal requests in handler. Reflection+custom annotations

I have one controller method(in real project it SOAP service's method):

@Slf4j
@RestController
public class ControllerDispatcher {

@PostMapping("request")
public void sendGenericRequest(@RequestBody MainRequest mainRequest) {}
}

In this method I receive MainRequest class. This class is wrapper(ExternalRequest). It contains 3 internal requests:

@Data
public class MainRequest {

    enum Type {FIRST, SECOND, LAST}

    private Type type;  //type of request
    private String request; //internal request in String format.
}

I need logic like spring dispather-servlet(something similar) and having caught the request to throw it in the desired method. I create Handler with custom annotation:

@InternalHandlerAnnotation
public class InternalRequestHandler {

    public void firstInternalrequest(FirstInternalRequest firstInternalRequest){

    }

    public void secondInternalrequest(SecondInternalRequest secondInternalRequest){

    }

    public void lastInternalrequest(LastInternalRequest lastInternalRequest){

    }
}

I want hadle MainRequest, unmarshal InternalRequest from MainRequest to class and redirect to concrete hadler's method.

It is 3 internal requests with I can receive:

@Data
public class FirstInternalRequest {
    private Long id;
    private String name;
    private int age;
}

@Data
public class SecondInternalRequest {
    private Long id;
    private String description;
}

@Data
public class LastInternalRequest {
    private Long id;
    private String hz;
    private int hz2;
}

Now I need mechanism for detect and redirect internal request to methods of handler class. I have resolcer:

@Component
public class HandlersResolver {
    private final ApplicationContext context;
    private Map<String, Object> beansWithAnnotation;

    public HandlersResolver(ApplicationContext context) {
        this.context = context;
    }

    @PostConstruct
    public void init() {
        beansWithAnnotation = context.getBeansWithAnnotation(InternalHandlerAnnotation.class);
        initHandler();
    }

    private void initHandler() {
        for (Map.Entry<String, Object> entry : beansWithAnnotation.entrySet()) {
            Annotation[] annotations = entry.getValue().getClass().getAnnotations();
            for (Annotation annotation : annotations) {
                if (annotation instanceof InternalHandlerAnnotation) {
                    Object beanWithMyAnnotation = entry.getValue();
                    Method[] declaredMethods = beanWithMyAnnotation.getClass().getDeclaredMethods();
                    for (Method declaredMethod : declaredMethods) {
                     Parameter[] parameters = declaredMethod.getParameters();
                     Parameter parameter = parameters[0];
                     Class<?> type = parameter.getType();
                     //convert String to type   
                }
                }
            }

        }
    }
}

I can detect bean with my annotation. Get methods and in each method get Parameter. but how to be next do not understand. How can I convert String from MainRequets to this type and cal method in handler?