【spring boot学习】Model&ModelMap&ModelAndView

1. Overview

In this article, we’ll look at the use of the core org.springframework.ui.Model, org.springframework.ui.ModelMap and org.springframework.web.servlet.ModelView provided by Spring MVC.

2. Maven Dependencies

Let’s start with the spring-context dependency in our pom.xml file:

<dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-context</artifactId>

<version>4.3.11.RELEASE</version>

</dependency>

The latest version of spring-context dependency can be found here.

For the ModelAndView, the spring-web dependency is required:

<dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-web</artifactId>

<version>4.3.11.RELEASE</version>

</dependency>

The latest versions of spring-web dependency can be found here.

And, if we use Thymeleaf as our view, we should add this dependency to pom.xml:

<dependency>

<groupId>org.thymeleaf</groupId>

<artifactId>thymeleaf-spring3</artifactId>

<version>3.0.8.RELEASE</version>

</dependency>

The latest version of Thymeleaf dependency can be found here.

3. Model

Let’s start with the most basic concept here – the Model.

Simply put, the model can supply attributes used for rendering views.

To provide a view with usable data, we simply add this data to its Model object. Additionally, maps with attributes can be merged with Model instances:

@GetMapping("/showViewPage")

public String passParametersWithModel(Model model) {

Map<String, String> map = new HashMap<>();

map.put("spring", "mvc");

model.addAttribute("message", "Baeldung");

model.mergeAttributes(map);

return "viewPage";

}

4. ModelMap

Just like the Model interface above, ModelMap is also used to pass values to render a view.

The advantage of ModelMap is it gives us the ability to pass a collection of values and treat these values as if they were within a Map:

@GetMapping("/printViewPage")

public String passParametersWithModelMap(ModelMap map) {

map.addAttribute("welcomeMessage", "welcome");

map.addAttribute("message", "Baeldung");

return "viewPage";

}

5. ModelAndView

The final interface to pass values to a view is the ModelAndView.

This interface allows us to pass all the information required by Spring MVC in one return:

@GetMapping("/goToViewPage")

public ModelAndView passParametersWithModelAndView() {

ModelAndView modelAndView = new ModelAndView("viewPage");

modelAndView.addObject("message", "Baeldung");

return modelAndView;

}

Constructors
Constructor and Description
`ModelAndView()` Default constructor for bean-style usage: populating bean properties instead of passing in constructor arguments.
`ModelAndView(java.lang.String viewName)` Convenient constructor when there is no model data to expose.
`ModelAndView(java.lang.String viewName, HttpStatus status)` Create a new ModelAndView given a view name and HTTP status.
`ModelAndView(java.lang.String viewName, java.util.Map<java.lang.String,?> model)` Create a new ModelAndView given a view name and a model.
`ModelAndView(java.lang.String viewName, java.util.Map<java.lang.String,?> model, HttpStatus status)` Create a new ModelAndView given a view name, model, and HTTP status.
`ModelAndView(java.lang.String viewName, java.lang.String modelName, java.lang.Object modelObject)` Convenient constructor to take a single model object.
`ModelAndView(View view)` Convenient constructor when there is no model data to expose.
`ModelAndView(View view, java.util.Map<java.lang.String,?> model)` Create a new ModelAndView given a View object and a model.
`ModelAndView(View view, java.lang.String modelName, java.lang.Object modelObject)` Convenient constructor to take a single model object.

`ModelAndView`	`addAllObjects(java.util.Map<java.lang.String,?> modelMap)` Add all attributes contained in the provided Map to the model.
`ModelAndView`	`addObject(java.lang.Object attributeValue)` Add an attribute to the model using parameter name generation.
`ModelAndView`	`addObject(java.lang.String attributeName, java.lang.Object attributeValue)` Add an attribute to the model.
`void`	`clear()` Clear the state of this ModelAndView object.
`java.util.Map<java.lang.String,java.lang.Object>`	`getModel()` Return the model map.
`protected java.util.Map<java.lang.String,java.lang.Object>`	`getModelInternal()` Return the model map.
`ModelMap`	`getModelMap()` Return the underlying `ModelMap` instance (never `null`).
`HttpStatus`	`getStatus()` Return the configured HTTP status for the response, if any.
`View`	`getView()` Return the View object, or `null` if we are using a view name to be resolved by the DispatcherServlet via a ViewResolver.
`java.lang.String`	`getViewName()` Return the view name to be resolved by the DispatcherServlet via a ViewResolver, or `null` if we are using a View object.
`boolean`	`hasView()` Indicate whether or not this `ModelAndView` has a view, either as a view name or as a direct `View` instance.
`boolean`	`isEmpty()` Return whether this ModelAndView object is empty, i.e.
`boolean`	`isReference()` Return whether we use a view reference, i.e.
`void`	`setStatus(HttpStatus status)` Set the HTTP status to use for the response.
`void`	`setView(View view)` Set a View object for this ModelAndView.
`void`	`setViewName(java.lang.String viewName)` Set a view name for this ModelAndView, to be resolved by the DispatcherServlet via a ViewResolver.
`java.lang.String`	`toString()` Return diagnostic information about this model and view.
`boolean`	`wasCleared()` Return whether this ModelAndView object is empty as a result of a call to `clear()` i.e.

6. The View

All the data, we place within these models, is used by a view – in general, a templated view to render the web page.

If we have a Thymeleaf template file targeted by our controller’s methods as their view. A parameter passed through the model will be accessible from within the thymeleaf HTML code:

<!DOCTYPE HTML>

<html xmlns:th="http://www.thymeleaf.org">

<head>

<title>Title</title>

</head>

<body>

<div>Web Application. Passed parameter : th:text="${message}"</div>

</body>

</html>

The parameter passed here is used through the syntax ${message}, which is known as a placeholder. The Thymeleaf template engine will replace this placeholder with an actual value from an attribute of the same name passed through the model.