Processing

  • 加载必要的上下文元素，包括 WebApplicationContext 和解析器（语言环境、主题、多部分文件）。

  • 搜索并执行适当的处理器，并准备一个模型进行渲染。

  • 处理异常，使用 HandlerExceptionResolver 进行自定义解析。

  • 提供 HTTP 缓存支持，允许处理器控制缓存行为。

  • 通过 Servlet 初始化参数来自定义 DispatcherServlet 实例，包括上下文配置、命名空间和异常处理行为。

DispatcherServlet 处理请求的步骤如下：

The DispatcherServlet processes requests as follows:

  • The WebApplicationContext is searched for and bound in the request as an attribute that the controller and other elements in the process can use. It is bound by default under the DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE key.

  • The locale resolver is bound to the request to let elements in the process resolve the locale to use when processing the request (rendering the view, preparing data, and so on). If you do not need locale resolving, you do not need the locale resolver.

  • The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it.

  • If you specify a multipart file resolver, the request is inspected for multiparts. If multiparts are found, the request is wrapped in a MultipartHttpServletRequest for further processing by other elements in the process. See Multipart Resolver for further information about multipart handling.

  • An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is run to prepare a model for rendering. Alternatively, for annotated controllers, the response can be rendered (within the HandlerAdapter) instead of returning a view.

  • If a model is returned, the view is rendered. If no model is returned (maybe due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled.

在`WebApplicationContext`中声明的`HandlerExceptionResolver`Bean 用于解析请求处理期间引发的异常。那些异常解析器允许自定义处理异常的逻辑。有关更多详细信息，请参阅Exceptions。

The HandlerExceptionResolver beans declared in the WebApplicationContext are used to resolve exceptions thrown during request processing. Those exception resolvers allow customizing the logic to address exceptions. See Exceptions for more details.

为了支持 HTTP 缓存，处理器可以使用 WebRequest 的 checkNotModified 方法，以及 HTTP Caching for Controllers 中所述的带注释控制器的其他选项。

For HTTP caching support, handlers can use the checkNotModified methods of WebRequest, along with further options for annotated controllers as described in HTTP Caching for Controllers.

你可以通过向 web.xml 文件中的 Servlet 声明添加 Servlet 初始化参数（init-param 元素）来自定义各个 DispatcherServlet 实例。下表列出了受支持的参数：

You can customize individual DispatcherServlet instances by adding Servlet initialization parameters (init-param elements) to the Servlet declaration in the web.xml file. The following table lists the supported parameters:

Table 1. DispatcherServlet initialization parameters
Parameter Explanation

contextClass

Class that implements ConfigurableWebApplicationContext, to be instantiated and locally configured by this Servlet. By default, XmlWebApplicationContext is used.

contextConfigLocation

String that is passed to the context instance (specified by contextClass) to indicate where contexts can be found. The string consists potentially of multiple strings (using a comma as a delimiter) to support multiple contexts. In the case of multiple context locations with beans that are defined twice, the latest location takes precedence.

namespace

Namespace of the WebApplicationContext. Defaults to [servlet-name]-servlet.

throwExceptionIfNoHandlerFound

Whether to throw a NoHandlerFoundException when no handler was found for a request. The exception can then be caught with a HandlerExceptionResolver (for example, by using an @ExceptionHandler controller method) and handled as any others.

As of 6.1, this property is set to true and deprecated.

Note that, if default servlet handling is also configured, unresolved requests are always forwarded to the default servlet and a 404 is never raised.