All about Dispatcher Servlet

Up to this point, you might have learned numerous Java & Spring related concepts such as RESTful services, microservices, security, and many more. However, in the process, core concepts often get overlooked, and the inner workings of these systems remain unclear.

Not to worry, if you've made it this far, let's embark on a journey together to understand the "DispatcherServlet."

1. DispatcherServlet with Spring:

Role:

In Spring’s MVC framework, the DispatcherServlet acts as the front controller. It intercepts incoming requests and manages the entire request processing lifecycle.

Configuration:

In a Spring-based application, you configure the DispatcherServlet typically using XML or Java-based configurations. This includes specifying its mappings, defining handler mappings, view resolvers, and other components to manage the flow of requests to appropriate controllers.

Spring's MVC Flow:

Upon receiving a request, DispatcherServlet identifies the appropriate controller based on URL mappings. It delegates request handling to the specific controller, which processes the request, obtains necessary data, and returns a ModelAndView or other response.

2. DispatcherServlet with Spring Boot:

Auto-Configuration:

In Spring Boot, the DispatcherServlet setup is streamlined. It’s automatically configured based on sensible defaults without explicit configuration. The servlet, along with default mappings, views, and necessary components, is automatically set up behind the scenes.

Simplified Setup:

Spring Boot’s convention over configuration approach means developers don’t have to explicitly define DispatcherServlet configurations. The servlet’s default behavior is applied, minimizing setup and allowing rapid development without extensive configuration.

3. DispatcherServlet without Spring:

In Servlet-based Web Applications:

In non-Spring-based Java web applications, developers manage servlets directly without the DispatcherServlet abstraction. They create servlet classes extending `javax.servlet.http.HttpServlet` and configure them in the `web.xml` file or through Servlet 3.0+ annotations.

Handling Requests:

Developers handle the entire request lifecycle explicitly within servlet classes, managing tasks such as request parsing, data processing, and response generation without the layered approach provided by the DispatcherServlet in Spring.

In summary, the DispatcherServlet plays a pivotal role in managing incoming requests in Spring-based applications, whether traditionally configured within Spring or in a streamlined manner within Spring Boot. However, in non-Spring-based applications, the direct handling of servlets bypasses the DispatcherServlet abstraction, requiring explicit control over the entire request-handling process.