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In a typical Spring Boot servlet application, Tomcat receives the HTTP request and passes it through servlet filters to Spring MVC’s DispatcherServlet. Spring MVC matches the request to a handler, invokes the appropriate controller method, and converts its return value into an HTTP response. Tomcat and Spring MVC work together, but they are separate layers.
The request path at a glance
A typical Spring MVC request follows this conceptual path:
HTTP client → embedded Tomcat connector → servlet filters → DispatcherServlet → handler mapping and adapter → @RestController method → HttpMessageConverter → HTTP response
This is a high-level servlet-stack view, not a description of Tomcat’s internal socket, thread, or protocol implementation. Configuration can also change which filters, servlets, or handlers participate.
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What Tomcat does—and what Spring MVC does
Spring Boot configures and starts an embedded servlet container for a servlet application. Tomcat is one supported server choice; Jetty and Undertow are alternatives. In the Spring Boot 3.3 reference, the default embedded server port is 8080. The application context obtains a ServletWebServerFactory; when Tomcat is selected, that is commonly the Tomcat implementation. See the Spring Boot 3.3 Servlet Web Applications reference for the version-specific details.
Tomcat provides the servlet container: it accepts servlet requests and dispatches them within the container. Spring MVC supplies the DispatcherServlet and the components that map requests to application handlers. The dispatcher is registered with the container; it is not part of Tomcat itself.
Filters run before the Spring MVC dispatcher
After the container receives a request, registered servlet filters run before the request reaches its mapped servlet. Spring Boot can register servlet and filter beans with the embedded container. By default, a single servlet maps to / and filters map to /*; mappings and filter order can be customized. These are conventional defaults, not a guaranteed trace for every application. The Spring Boot 3.3 servlet reference describes servlet and filter registration.
A filter may affect a request before it enters Spring MVC, and the request may not reach a controller at all. Other servlets, static-resource handling, errors, custom mappings, and filter behavior can alter the path.
DispatcherServlet finds the Spring MVC handler
Spring Framework describes DispatcherServlet as a front controller: it provides a shared request-processing algorithm and delegates concrete work to configurable components. In practice, Spring MVC’s handler-mapping machinery checks the request against registered endpoint mappings. For annotation-based controllers, mappings are declared with @RequestMapping and composed annotations such as @GetMapping. An adapter then invokes the selected handler, with Spring MVC resolving method arguments along the way.
For Spring Boot 3.3, path matching uses PathPatternParser by default, and the documentation describes customization and pattern restrictions. Matching details are version- and configuration-sensitive, so do not assume every pattern behaves identically across Spring Boot releases. See the Spring Boot 3.3 MVC reference.
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What @RestController changes
@RestController belongs to Spring MVC, not exclusively to Spring Boot. It combines controller behavior with response-body semantics: a method’s return value is treated as data for the response rather than, as is common with a regular @Controller, a view name. Spring Boot makes MVC setup convenient through auto-configuration when the relevant dependencies are present. The Spring getting-started guide explains the annotation’s behavior.
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The annotation does not change the underlying HTTP transport or make Tomcat select the method. Spring MVC selects and invokes the handler; response-body processing then uses a suitable HttpMessageConverter.
How a return value becomes an HTTP response
A message converter writes the controller’s return value in a representation supported by the application. JSON is common, but it is not guaranteed for every setup: the available converter depends on the classpath and configuration, and content negotiation—including the request’s Accept header—can affect the response media type.
The Spring Boot 4.1.1 Spring MVC how-to describes default JSON rendering when Jackson 3 is available. That is a release-specific detail; it should not be treated as a universal requirement for older Spring Boot versions.
Why the actual route can differ
- Servlet and filter configuration: Additional servlets, custom URL mappings, filter mappings, and filter order affect the container-level path.
- MVC configuration: Custom handler mappings, controller declarations, path-matching settings, and servlet paths can affect which handler is selected.
- Application type: This flow describes Spring MVC on the servlet stack. It is not a WebFlux request path; reactive applications should not be described as passing through Tomcat’s
DispatcherServlet. - Return-value handling: Converter dependencies, response type, content negotiation, and custom configuration determine how response data is represented.
For the framework-level role of the dispatcher, see the Spring Framework Reference: DispatcherServlet. Spring Boot’s MVC auto-configuration and annotation context are also covered in the Spring getting-started guide and the legacy Spring Boot reference.
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