In the Spring MVC framework, the DispatcherServlet is a crucial component that acts as the front controller. It is responsible for routing incoming HTTP requests to the appropriate handlers (controllers) based on the request URL. This design pattern promotes a clean separation of concerns and enhances the maintainability of web applications.
The DispatcherServlet performs several key functions:
Request Handling: It intercepts all incoming requests and delegates them to the appropriate controller based on URL patterns.
Response Rendering: After processing the request, it manages the rendering of the view (typically a JSP, Thymeleaf, or other view technologies).
Integration with Other Components: It works with various Spring components like handler mappings, view resolvers, and exception resolvers to handle the request-response lifecycle efficiently.
Application Context: The DispatcherServlet creates and manages its own application context, which can be used to load beans specific to the web layer.
The lifecycle of the DispatcherServlet can be summarized in the following steps:
HandlerMapping.ViewResolver.In a Spring application, you typically define the DispatcherServlet in the web.xml file or, in modern applications using Spring Boot, it is auto-configured.
Here’s an example of how to configure DispatcherServlet in a traditional Spring MVC application using web.xml:
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<servlet>
<servlet-name>dispatcher</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcher</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/spring/applicationContext.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
</web-app>
In a Spring Boot application, the DispatcherServlet is automatically configured, and you typically don’t need to define it explicitly. Instead, you can use annotations to configure your controllers and request mappings.
In a Spring Boot application, you do not need to explicitly define the DispatcherServlet in web.xml. Instead, the Spring Boot framework auto-configures it for you based on the dependencies present in your pom.xml.
DispatcherServlet will handle all incoming requests by default (using the / URL pattern). You can change this by customizing the servlet registration in your application code, but for most applications, the default behavior is sufficient.The @Controller annotation indicates that a class serves as a controller in the Spring MVC framework. Each method in the controller can handle different HTTP requests:
@GetMapping: This annotation is used to map HTTP GET requests to specific handler methods. In our example, showForm is mapped to the /user URL.
@PostMapping: This annotation is used for handling HTTP POST requests. The submitForm method handles form submissions.
@ModelAttribute: This annotation binds request parameters to a model object, making it easy to work with form data.
In our application, the model is represented by the User class. When a user submits the form, the data is bound to a User object, which is then added to the model for rendering in the view.
In a full-fledged application, you will also need to handle exceptions gracefully. Spring MVC provides various ways to handle exceptions:
@ExceptionHandler: You can define a method in your controller to handle specific exceptions.
ControllerAdvice: You can create a global exception handler that applies to all controllers.