Class DispatcherServlet

All Implemented Interfaces:
Servlet, ServletConfig, Serializable, Aware, ApplicationContextAware, EnvironmentAware, EnvironmentCapable

public class DispatcherServlet extends FrameworkServlet
Central dispatcher for HTTP request handlers/controllers, e.g. for web UI controllers or HTTP-based remote service exporters. Dispatches to registered handlers for processing a web request, providing convenient mapping and exception handling facilities.

This servlet is very flexible: It can be used with just about any workflow, with the installation of the appropriate adapter classes. It offers the following functionality that distinguishes it from other request-driven web MVC frameworks:

  • It is based around a JavaBeans configuration mechanism.
  • It can use any HandlerMapping implementation - pre-built or provided as part of an application - to control the routing of requests to handler objects. Default is BeanNameUrlHandlerMapping and RequestMappingHandlerMapping. HandlerMapping objects can be defined as beans in the servlet's application context, implementing the HandlerMapping interface, overriding the default HandlerMapping if present. HandlerMappings can be given any bean name (they are tested by type).
  • It can use any HandlerAdapter; this allows for using any handler interface. Default adapters are HttpRequestHandlerAdapter, SimpleControllerHandlerAdapter, for Spring's HttpRequestHandler and Controller interfaces, respectively. A default RequestMappingHandlerAdapter will be registered as well. HandlerAdapter objects can be added as beans in the application context, overriding the default HandlerAdapters. Like HandlerMappings, HandlerAdapters can be given any bean name (they are tested by type).
  • The dispatcher's exception resolution strategy can be specified via a HandlerExceptionResolver, for example mapping certain exceptions to error pages. Default are ExceptionHandlerExceptionResolver, ResponseStatusExceptionResolver, and DefaultHandlerExceptionResolver. These HandlerExceptionResolvers can be overridden through the application context. HandlerExceptionResolver can be given any bean name (they are tested by type).
  • Its view resolution strategy can be specified via a ViewResolver implementation, resolving symbolic view names into View objects. Default is InternalResourceViewResolver. ViewResolver objects can be added as beans in the application context, overriding the default ViewResolver. ViewResolvers can be given any bean name (they are tested by type).
  • If a View or view name is not supplied by the user, then the configured RequestToViewNameTranslator will translate the current request into a view name. The corresponding bean name is "viewNameTranslator"; the default is DefaultRequestToViewNameTranslator.
  • The dispatcher's strategy for resolving multipart requests is determined by a MultipartResolver implementation. An implementation for standard Servlet multipart processing is included. The MultipartResolver bean name is "multipartResolver"; default is none.
  • Its locale resolution strategy is determined by a LocaleResolver. Out-of-the-box implementations work via HTTP accept header, cookie, or session. The LocaleResolver bean name is "localeResolver"; default is AcceptHeaderLocaleResolver.
  • Its theme resolution strategy is determined by a ThemeResolver. Implementations for a fixed theme and for cookie and session storage are included. The ThemeResolver bean name is "themeResolver"; default is FixedThemeResolver. Theme support is deprecated as of 6.0 with no direct replacement.

NOTE: The @RequestMapping annotation will only be processed if a corresponding HandlerMapping (for type-level annotations) and/or HandlerAdapter (for method-level annotations) is present in the dispatcher. This is the case by default. However, if you are defining custom HandlerMappings or HandlerAdapters, then you need to make sure that a corresponding custom RequestMappingHandlerMapping and/or RequestMappingHandlerAdapter is defined as well - provided that you intend to use @RequestMapping.

A web application can define any number of DispatcherServlets. Each servlet will operate in its own namespace, loading its own application context with mappings, handlers, etc. Only the root application context as loaded by ContextLoaderListener, if any, will be shared.

DispatcherServlet may be injected with a web application context, rather than creating its own internally. This is useful in Servlet 3.0+ environments, which support programmatic registration of servlet instances. See the DispatcherServlet(WebApplicationContext) javadoc for details.

Rod Johnson, Juergen Hoeller, Rob Harrop, Chris Beams, Rossen Stoyanchev, Sebastien Deleuze
See Also: