spring MVC model

使用spring MVC的人都知道,控制器是通过Model把数据传到view层的.那么它们具体是通过什么来定位传递的数据呢?

比如控制器中的一个方法:

Java代码  

1. @RequestMapping(value = "/add",method=RequestMethod.GET)  
2.     public String addInputNews(String practiceWay, Model model) {  
3.         commonAction(model);  
4.         List<RoleLevel> roles=this.roleLevelDao.getAll();  
5.         model.addAttribute("roles",roles);//选择上级  
6.         model.addAttribute(new RoleLevel());  
7.         return jspFolder+"/add";  
8.     }  

 在view层可以通过${roles}来获取数据,即view层通过model中的key进行获取.

那么问题来了,如果是model.addAttribute(roles);//选择上级 呢?没有key?!

经过查spring MVC官方资料,view层可以通过${roleLevelList } 来获取数据.

具体是什么依据呢?

以下是官方资料:

The ModelMap class is essentially a glorified Map that can make adding objects that are to be displayed in (or on) a View adhere to a common naming convention. Consider the following Controller implementation; notice that objects are added to the ModelAndView without any associated name specified.

public class DisplayShoppingCartController implements Controller {

    public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

        List cartItems = // get a List of CartItem objects
        User user = // get the User doing the shopping

        ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name

        mav.addObject(cartItems); <-- look ma, no name, just the object
        mav.addObject(user); <-- and again ma!

        return mav;
    }
}

The ModelAndView class uses a ModelMap class that is a custom Map implementation that automatically generates a key for an object when an object is added to it. The strategy for determining the name for an added object is, in the case of a scalar object such as User, to use the short class name of the object's class. The following examples are names that are generated for scalar objects put into a ModelMap instance.

The strategy for generating a name after adding a Set or a List is to peek into the collection, take the short class name of the first object in the collection, and use that with List appended to the name. The same applies to arrays although with arrays it is not necessary to peek into the array contents. A few examples will make the semantics of name generation for collections clearer: