What is Model in ModelAndView from Spring MVC

Question

Having this basic function  protected ModelAndView handleRequestInternal                    return new ModelAndView  welcomePage    WelcomeMessage   message       I know that this will return modelandView   I know that welcomePage is my viewname so that means something like welcomepage jsp will get called   But I am confused with what is Model part   What is WelcomeMessage and message and how Model work in that scenario

User · Answer

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);

User · Answer

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 - gt  which will viewed      errorMessage  is the variable that could be displayed in page using - gt      errorMessage        Registered Successfully   or  ERROR    is the message will be printed based on   if-else condition

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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  quot welcomePage quot    quot WelcomeMessage quot   message

[spring] What is Model in ModelAndView from Spring MVC?

Examples related to spring

Examples related to spring-mvc