ViewResolver in Spring MVC

Welcome to this comprehensive guide on utilizing the ViewResolver interface in Spring MVC. As a core component of Spring's MVC framework, ViewResolver plays a pivotal role in mapping view names to actual views. Whether you're new to Spring MVC or looking to refresh your understanding, this article aims to provide a clear and detailed examination of ViewResolver

Understanding ViewResolver in Spring MVC

In the context of Spring MVC, the ViewResolver interface assists in mapping logical view names, returned by the Controller, to actual view objects, such as JSPs or Thymeleaf templates. It forms a bridge between the controller and the view component of the MVC architecture, determining which view to display based on the logical view name

The Role of ViewResolver in the Spring MVC Flow

When a request is processed by a Spring MVC application, the request is received by the DispatcherServlet, which then routes it to the appropriate controller. The controller performs the required business logic and returns a ModelAndView object, containing the model data and the logical name of the view

This logical view name is passed onto the ViewResolver, which then resolves it to a specific view technology, such as JSP, Thymeleaf, or FreeMarker. The DispatcherServlet will render this view, along with the model data, back to the client.

Implementing ViewResolver: A Step-by-Step Guide

Now that we've understood the concept of ViewResolver, let's see how we can implement it in a Spring MVC application.

Step 1 − Setting up the Project

Create a new Spring MVC project using Spring Boot Initializer or Spring STS. Include necessary dependencies like Spring Web MVC and Thymeleaf

Step 2 − Configuring ViewResolver

In a typical Spring MVC application, ViewResolver is configured in the application's configuration class, annotated with @Configuration. Here is an example of configuring a ViewResolver using InternalResourceViewResolver for JSP views:

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.example.demo")
public class AppConfig implements WebMvcConfigurer {
   @Bean
   public ViewResolver viewResolver() {
      InternalResourceViewResolver resolver = new InternalResourceViewResolver();
      resolver.setPrefix("/WEB-INF/views/");
      resolver.setSuffix(".jsp");
      resolver.setOrder(1);
      return resolver;
   }
}

In the above code, we've set the prefix and suffix to denote that our views are JSP files located in /WEB-INF/views/ directory. The setOrder(1) method sets the priority of this ViewResolver.

Step 3 − Creating a Controller

Next, we'll create a controller that returns a ModelAndView object. The logical view name returned here will be resolved by our ViewResolver

@Controller
public class HomeController {
   @RequestMapping("/")
   public ModelAndView home() {
      ModelAndView modelAndView = new ModelAndView("home");
      modelAndView.addObject("message", "Welcome to Spring MVC!");
      return modelAndView;
   }
}

In the above code, "home" is the logical view name. Our ViewResolver will resolve this to /WEB-INF/views/home.jsp.

Step 4 − Creating the View

Finally, create a JSP file named home.jsp in the /WEB-INF/views/ directory. This is the view that will be rendered to the user.

Multiple ViewResolvers

In more complex applications, you might want to use multiple ViewResolvers. For instance, you may want to use Thymeleaf for certain views and JSP for others. In this scenario, you can configure multiple ViewResolvers and set their order of precedence using the setOrder() method. The ViewResolver with the lowest order value has the highest precedence. If a ViewResolver can't resolve a view, the next ViewResolver in order is tried.

Custom ViewResolver

While Spring provides ready-to-use ViewResolver implementations for most popular view technologies, you might sometimes need to create a custom ViewResolver. This could be useful if you're using a view technology that Spring doesn't support out-of-the-box, or if you need more control over how views are resolved.

To create a custom ViewResolver, you'll need to create a class that implements the ViewResolver interface and override the resolveViewName() method. Here's a simple example −

public class CustomViewResolver implements ViewResolver {
   @Override
   public View resolveViewName(String viewName, Locale locale) throws Exception {
      // Custom logic to resolve view
   }
}

In the resolveViewName() method, you can implement your custom logic for resolving views. Once done, you can add your CustomViewResolver to your application's configuration just like any other ViewResolver

Conclusion

The ViewResolver in Spring MVC is an essential component that links the Controller and View layers of the MVC architecture. Understanding how to configure and utilize ViewResolvers effectively can greatly improve your ability to create robust and flexible Spring MVC applications.

With its out-of-the-box support for a wide range of view technologies, and the flexibility to implement custom view resolution strategies, the ViewResolver interface is a perfect demonstration of Spring's "Make the common case easy, and the complex case possible" philosophy.