如何在Spring-MVC方法中绑定抽象类的子类？

Question

Given a "save" method in a Spring-MVC controller:

@RequestMapping(value = "/save")
public void save(@ModelAttribute(MY_KEY) final MyModel myModel) { ... }

with a property in the myModel parameter that is an abstract class:

public class MyModel {
    public AbstractFruit fruit;
}

Is there any way of specifying use of a particular subclass (eg Apple ) in the request?

Answer 1

You can use custom init binder method in your controller class:

// Additionally using MY_KEY as "value" parameter of this annotation
// is not working in some cases
@InitBinder
public void initBinder(WebDataBinder webDataBinder, HttpServletRequest servletRequest) {

    // Probably you only want to init this when form is submitted
    if (!"POST".equalsIgnoreCase(httpServletRequest.getMethod()) {
        return;
    }

    // Filter out all request when we have nothing to do
    Object nonCastedTarget = webDataBinder.getTarget();
    if (nonCastedTarget == null || !(nonCastedTarget instanceof MyModel)) {
        return;
    }

    MyModel target = (MyModel) nonCastedTarget;
    if (/* some condition */) {
        target.setFruit(new Apple());
    } else {
        target.setFruit(new Banana());
    }
}

Spring form binding mechanism will then correctly set all fields in Apple/Banana class.