Usage Instructions for Model Objects in SpringMVC

The main function of model objects is to save data, which can be used to bring data to the front end.

Commonly used model objects are the following:

ModelAndView (As the name implies, models and views can carry both data information and view information. The general usage is as follows.)

    /**
     * ModelAndView  Binding data to a view   ( ModelMap Used to transfer data  View Object for jumping) 
     * @return
     * @throws Exception
     */
    @RequestMapping(value="/case2")
    public ModelAndView case2() throws Exception {
        ModelAndView mav = new ModelAndView();
        mav.setViewName("/demo03/model.jsp");
        mav.addObject("sex", "boy");
        return mav;
    }

Map , and modelAndView Principle 1, the same is to put data one by one requestScope In, the data fetched from the front end is also ${model data}

    /**
     *  Target methods can be added  Map  Type ( In fact, it can also be  Model  Type or  ModelMap  Type ) Parameters of . 
     * @param map
     * @return
     */
    @RequestMapping("/case")
    public String case1(Map map) throws Exception{
        map.put("sex", " Achieve success !!");
        return "/demo03/model.jsp";
    }

@SessionAttributes (Equivalent to creating session Object to the session Put data in the object, which is perfectly solved with 1 annotation here)

The basic format is as follows:

/**
 * @SessionAttributes  In addition to specifying the attributes that need to be put into the session by the attribute name, ( What is actually used is  value  Attribute value ),
 *  You can also specify which model attributes need to be put into the session by the object type of the model attributes ( What is actually used is  types  Attribute value )
 *  Attention :  This annotation can only be placed on the top of the class .  And can't modify the method when it is in map Neutralization session Medium   Each has stored it 1 Entity classes, 1 A String String of class 
 */
@SessionAttributes("user")
@Controller
public class SessionController { 
 @ModelAttribute("user")
 public User getUser(){
  User user = new User();
  return user;
 }
 /**
  * http://localhost:8080/s/s1?id=1
  *  Request forwarding  forward:  No processing is required 
  *  Request redirection  redirect:  Use SessionAttribute Mode   Used to pass to in redirection    Stores the value in the session Medium   "Remember to clear when you use it" 
  * @return
  * @throws Exception
  */
 @RequestMapping(value="/s1",method=RequestMethod.GET)
 public String case1(@ModelAttribute("user") User user) throws Exception{
  return "redirect:/s2";
 }
 
 @RequestMapping(value="/s2",method=RequestMethod.GET)
 public String case2(Map map,HttpServletResponse res,SessionStatus sessionStatus) throws Exception{
  User user=(User)map.get("user");
  res.getWriter().println(user.getId());
  sessionStatus.setComplete();
  return null;
 }
}

Difference between Model and ModelAndView in SpringMVC

1. Main differences

Model Is the default parameter that exists in every request, using its addAttribute() Method to pass the server's value to the jsp Page;

ModelAndView Include model And view Two parts, when using, you need to instantiate yourself and use ModelMap Used to pass values, or set view Name of

2. Examples

1) Use Model Value transfer

@RequestMapping(value="/list-books")
 private String getAllBooks(Model model){
  logger.error("/list-books");
  List<Book> books= bookService.getAllBooks();
  model.addAttribute("books", books);
  return "BookList";
 }

In jsp Page profit ${books} You can take out the value

2) Use ModelAndView There are two ways to pass values. The different methods are in jsp The value of the page is different, and the value of the page is set view Name of

public ModelAndView resolveException(HttpServletRequest request, HttpServletResponse response,
        Object handler, Exception ex) {
        LibraryException le=null;
        if(ex instanceof LibraryException){
            le=(LibraryException)ex;
        }else{
            le=new LibraryException(" System unknown exception! ");
        }
 
        ModelAndView modelAndView=new ModelAndView();
        modelAndView.addObject("exception",le.getMessage());
        modelAndView.getModel().put("exception",le.getMessage());
        modelAndView.setViewName("error"); 
        return modelAndView;
    }

jsp Medium ${requestScope.exception1} Can be removed exception1 The value of;

jsp Medium ${exception2} Can be removed exception2 Value of