java - 如何在Spring-MVC方法中绑定(bind)抽象类的子类？

Question

给定 Spring-MVC Controller 中的“保存”方法:

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

myModel 参数中的属性是一个抽象类:

public class MyModel {
    public AbstractFruit fruit;
}

是否有任何方法可以在请求中指定使用特定子类(例如 Apple)？

Answer 1

您可以在 Controller 类中使用自定义 init binder 方法:

// 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 表单绑定(bind)机制将正确设置 Apple/Banana 类中的所有字段。