从 SpringMVC 来看 ModelAndView 中的模型是什么？

有这个基本功能的

protected ModelAndView handleRequestInternal(...) {
...
return new ModelAndView("welcomePage", "WelcomeMessage", message);
}

我知道这将返回 model 和 View。 我知道 welcomePage是我的视图名，所以这意味着像 welcomepage.jsp这样的东西将被调用。

但我对什么是模型部分感到困惑。 什么是 WelcomeMessage和 message? 在这种情况下，Model 是如何工作的？

144394 次浏览
小开

Well, WelcomeMessage is just a variable name for message (actual model with data). Basically, you are binding the model with the welcomePage here. The Model (message) will be available in welcomePage.jsp as WelcomeMessage. Here is a simpler example:

ModelAndView("hello","myVar", "Hello World!");

In this case, my model is a simple string (In applications this will be a POJO with data fetched for DB or other sources.). I am assigning it to myVar and my view is hello.jsp. Now, myVar is available for me in hello.jsp and I can use it for display.

In the view, you can access the data though:

${myVar}

Similarly, You will be able to access the model through WelcomeMessage variable.

小开
最佳答案

The model presents a placeholder to hold the information you want to display on the view. It could be a string, which is in your above example, or it could be an object containing bunch of properties.

Example 1

If you have...

return new ModelAndView("welcomePage","WelcomeMessage","Welcome!");

... then in your jsp, to display the message, you will do:-

Hello Stranger! ${WelcomeMessage} // displays Hello Stranger! Welcome!

Example 2

If you have...

MyBean bean = new MyBean();
bean.setName("Mike!");
bean.setMessage("Meow!");


return new ModelAndView("welcomePage","model",bean);

... then in your jsp, you can do:-

Hello ${model.name}! {model.message} // displays Hello Mike! Meow!
小开

It is all explained by the javadoc for the constructor. It is a convenience constructor that populates the model with one attribute / value pair.

So ...

   new ModelAndView(view, name, value);

is equivalent to:

   Map model = ...
model.put(name, value);
new ModelAndView(view, model);
小开 
new ModelAndView("welcomePage", "WelcomeMessage", message);

is shorthand for

ModelAndView mav = new ModelAndView();
mav.setViewName("welcomePage");
mav.addObject("WelcomeMessage", message);

Looking at the code above, you can see the view name is "welcomePage". Your ViewResolver (usually setup in .../WEB-INF/spring-servlet.xml) will translate this into a View. The last line of the code sets an attribute in your model (addObject("WelcomeMessage", message)). That's where the model comes into play.

小开

Here in this case, we are having 3 parameter's in the Method namely ModelandView.
According to this question, the first parameter is easily understood. It represents the View which will be displayed to the client.
The other two parameters are just like The Pointer and The Holder
Hence you can sum it up like this

ModelAndView(View, Pointer, Holder);

The Pointer just points the information in the The Holder

When the Controller binds the View with this information, then in the said process, you can use The Pointer in the JSP page to access the information stored in The Holder to display that respected information to the client.
Here is the visual depiction of the respected process.

return new ModelAndView("welcomePage", "WelcomeMessage", message);

enter image description here

小开

ModelAndView: The name itself explains it is data structure which contains Model and View data. 

Map() model=new HashMap();
model.put("key.name", "key.value");
new ModelAndView("view.name", model);


// or as follows


ModelAndView mav = new ModelAndView();
mav.setViewName("view.name");
mav.addObject("key.name", "key.value");

if model contains only single value, we can write as follows:

ModelAndView("view.name","key.name", "key.value");
小开 
@RequestMapping(value="/register",method=RequestMethod.POST)
public ModelAndView postRegisterPage(HttpServletRequest request,HttpServletResponse response,
@ModelAttribute("bean")RegisterModel bean)
{
RegisterService service = new RegisterService();
boolean b = service.saveUser(bean);


if(b)
{
return new ModelAndView("registerPage","errorMessage","Registered Successfully!");
}
else
{
return new ModelAndView("registerPage","errorMessage","ERROR!!");
}
}






/*  "registerPage" is the .jsp page -> which will viewed.
/* "errorMessage" is the variable that could be displayed in page using -> **${errorMessage}**
/* "Registered Successfully!" or "ERROR!!" is the message will be printed based on **if-else condition**

提交答案