DispatcherServlet (Spring Framework)

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org.springframework.web.servlet
Class DispatcherServlet

java.lang.Object
  javax.servlet.GenericServlet
      javax.servlet.http.HttpServlet
          org.springframework.web.servlet.HttpServletBean
              org.springframework.web.servlet.FrameworkServlet
                  org.springframework.web.servlet.DispatcherServlet

All Implemented Interfaces:: Serializable, Servlet, ServletConfig

public class DispatcherServlet
extends FrameworkServlet

Central dispatcher for use within the web MVC framework, e.g. for web UI controllers or HTTP-based remote service exporters. Dispatches to registered handlers for processing a web request.

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 - whether standard, or provided as part of an application - to control the routing of requests to handler objects. Default is BeanNameUrlHandlerMapping. HandlerMapping objects can be define as beans in the servlet's application context that implement the HandlerMapping interface. HandlerMappings can be given any bean name (they are tested by type).
It can use any HandlerAdapter; this allows to use any handler interface. Default is SimpleControllerHandlerAdapter, for Spring's Controller interface. Additional HandlerAdapter objects can be added through the application context. Like HandlerMappings, HandlerAdapters can be given any bean name (tested by type).
Its exception resolution strategy can be specified via a HandlerExceptionResolver, for example mapping certain exceptions to error pages. Default is none. Additional HandlerExceptionResolvers can be added through the application context. HandlerExceptionResolver can be given any bean name (tested by type).
Its view resolution strategy can be specified via a ViewResolver implementation, resolving symbolic view names into View objects. Default is InternalResourceViewResolver. Additional ViewResolver objects can be added through the application context. ViewResolvers can be given any bean name (tested by type).
Its strategy for resolving multipart requests is determined by a MultipartResolver implementation. Implementations for Jakarta Commons FileUpload and Jason Hunter's COS are included. The MultipartResolver bean name is "multipartResolver"; default is none.
Its locale resolution strategy is determined by a LocaleResolver implementation. 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 implementation. Implementations for a fixed theme and for cookie and session storage are included. The ThemeResolver bean name is "themeResolver"; default is FixedThemeResolver.

A web application can use any number of DispatcherServlets. Each servlet will operate in its own namespace. Only the root application context will be shared.

This class and the MVC approach it delivers is discussed in Chapter 12 of Expert One-On-One J2EE Design and Development by Rod Johnson (Wrox, 2002). Note that it is called ControllerServlet there; it has been renamed since to emphasize its dispatching role and avoid confusion with Controller objects that the DispatcherServlet will dispatch to.

Author:: Rod Johnson, Juergen Hoeller
See Also:: ContextLoaderListener, HandlerMapping, BeanNameUrlHandlerMapping, HandlerAdapter, SimpleControllerHandlerAdapter, Controller, HandlerExceptionResolver, SimpleMappingExceptionResolver, ViewResolver, InternalResourceViewResolver, MultipartResolver, CommonsMultipartResolver, LocaleResolver, AcceptHeaderLocaleResolver, ThemeResolver, FixedThemeResolver, Serialized Form

Field Summary
`static String`	`HANDLER_EXCEPTION_RESOLVER_BEAN_NAME` Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace.
`static String`	`HANDLER_EXECUTION_CHAIN_ATTRIBUTE` Request attribute to hold the currently chosen HandlerExecutionChain.
`static String`	`HANDLER_MAPPING_BEAN_NAME` Well-known name for the HandlerMapping object in the bean factory for this namespace.
`static String`	`LOCALE_RESOLVER_ATTRIBUTE` Request attribute to hold current locale, retrievable by views.
`static String`	`LOCALE_RESOLVER_BEAN_NAME` Well-known name for the LocaleResolver object in the bean factory for this namespace.
`static String`	`MULTIPART_RESOLVER_ATTRIBUTE` Request attribute to hold current multipart resolver, retrievable by views/binders.
`static String`	`MULTIPART_RESOLVER_BEAN_NAME` Well-known name for the MultipartResolver object in the bean factory for this namespace.
`static String`	`PAGE_NOT_FOUND_LOG_CATEGORY` Log category to use when no mapped handler is found for a request.
`protected static Log`	`pageNotFoundLogger` Additional logger to use when no mapped handler is found for a request.
`static String`	`THEME_RESOLVER_ATTRIBUTE` Request attribute to hold current theme, retrievable by views.
`static String`	`THEME_RESOLVER_BEAN_NAME` Well-known name for the ThemeResolver object in the bean factory for this namespace.
`static String`	`VIEW_RESOLVER_BEAN_NAME` Well-known name for the ViewResolver object in the bean factory for this namespace.
`static String`	`WEB_APPLICATION_CONTEXT_ATTRIBUTE` Request attribute to hold current web application context.

Fields inherited from class org.springframework.web.servlet.FrameworkServlet

DEFAULT_CONTEXT_CLASS, DEFAULT_NAMESPACE_SUFFIX, SERVLET_CONTEXT_PREFIX

Fields inherited from class org.springframework.web.servlet.HttpServletBean

logger

Constructor Summary
`DispatcherServlet()`

Method Summary
`protected HttpServletRequest`	`checkMultipart(HttpServletRequest request)` Convert the request into a multipart request, and make multipart resolver available.
`protected void`	`doDispatch(HttpServletRequest request, HttpServletResponse response)` Process the actual dispatching to the handler.
`protected void`	`doService(HttpServletRequest request, HttpServletResponse response)` Expose the DispatcherServlet-specific request attributes and delegate to `doDispatch` for the actual dispatching.
`protected List`	`getDefaultStrategies(Class strategyInterface)` Create a List of default strategy objects for the given strategy interface.
`protected Object`	`getDefaultStrategy(Class strategyInterface)` Return the default strategy object for the given strategy interface.
`protected HandlerExecutionChain`	`getHandler(HttpServletRequest request, boolean cache)` Return the HandlerExecutionChain for this request.
`protected HandlerAdapter`	`getHandlerAdapter(Object handler)` Return the HandlerAdapter for this handler object.
`protected long`	`getLastModified(HttpServletRequest request)` Override HttpServlet's `getLastModified` method to evaluate the Last-Modified value of the mapped handler.
`protected void`	`initFrameworkServlet()` Overridden method, invoked after any bean properties have been set and the WebApplicationContext and BeanFactory for this namespace is available.
`protected void`	`noHandlerFound(HttpServletRequest request, HttpServletResponse response)` No handler found -> set appropriate HTTP response status.
`protected ModelAndView`	`processHandlerException(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)` Determine an error ModelAndView via the registered HandlerExceptionResolvers.
`protected void`	`render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)` Render the given ModelAndView.
`protected View`	`resolveViewName(String viewName, Map model, Locale locale, HttpServletRequest request)` Resolve the given view name into a View object (to be rendered).
`void`	`setCleanupAfterInclude(boolean cleanupAfterInclude)` Set whether to perform cleanup of request attributes after an include request, i.e. whether to reset the original state of all request attributes after the DispatcherServlet has processed within an include request.
`void`	`setDetectAllHandlerExceptionResolvers(boolean detectAllHandlerExceptionResolvers)` Set whether to detect all HandlerExceptionResolver beans in this servlet's context.
`void`	`setDetectAllHandlerMappings(boolean detectAllHandlerMappings)` Set whether to detect all HandlerMapping beans in this servlet's context.
`void`	`setDetectAllViewResolvers(boolean detectAllViewResolvers)` Set whether to detect all ViewResolver beans in this servlet's context.

Methods inherited from class org.springframework.web.servlet.FrameworkServlet

createWebApplicationContext, destroy, doDelete, doGet, doPost, doPut, getContextClass, getContextConfigLocation, getNamespace, getServletContextAttributeName, getUsernameForRequest, getWebApplicationContext, initServletBean, initWebApplicationContext, isPublishContext, isPublishEvents, setContextClass, setContextConfigLocation, setNamespace, setPublishContext, setPublishEvents

Methods inherited from class org.springframework.web.servlet.HttpServletBean

addRequiredProperty, init, initBeanWrapper

Methods inherited from class javax.servlet.http.HttpServlet

doHead, doOptions, doTrace, service, service

Methods inherited from class javax.servlet.GenericServlet

getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MULTIPART_RESOLVER_BEAN_NAME

public static final String MULTIPART_RESOLVER_BEAN_NAME

Well-known name for the MultipartResolver object in the bean factory for this namespace.

See Also:: Constant Field Values

LOCALE_RESOLVER_BEAN_NAME

public static final String LOCALE_RESOLVER_BEAN_NAME

Well-known name for the LocaleResolver object in the bean factory for this namespace.

See Also:: Constant Field Values

THEME_RESOLVER_BEAN_NAME

public static final String THEME_RESOLVER_BEAN_NAME

Well-known name for the ThemeResolver object in the bean factory for this namespace.

See Also:: Constant Field Values

HANDLER_MAPPING_BEAN_NAME

public static final String HANDLER_MAPPING_BEAN_NAME

Well-known name for the HandlerMapping object in the bean factory for this namespace. Only used when "detectAllHandlerMappings" is turned off.

See Also:: setDetectAllViewResolvers(boolean), Constant Field Values

HANDLER_EXCEPTION_RESOLVER_BEAN_NAME

public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME

Well-known name for the HandlerExceptionResolver object in the bean factory for this namespace. Only used when "detectAllHandlerExceptionResolvers" is turned off.

See Also:: setDetectAllViewResolvers(boolean), Constant Field Values

VIEW_RESOLVER_BEAN_NAME

public static final String VIEW_RESOLVER_BEAN_NAME

Well-known name for the ViewResolver object in the bean factory for this namespace. Only used when "detectAllViewResolvers" is turned off.

See Also:: setDetectAllViewResolvers(boolean), Constant Field Values

HANDLER_EXECUTION_CHAIN_ATTRIBUTE

public static final String HANDLER_EXECUTION_CHAIN_ATTRIBUTE

Request attribute to hold the currently chosen HandlerExecutionChain. Only used for internal optimizations.

WEB_APPLICATION_CONTEXT_ATTRIBUTE

public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE

Request attribute to hold current web application context. Otherwise only the global web app context is obtainable by tags etc.

See Also:: RequestContextUtils.getWebApplicationContext(javax.servlet.ServletRequest)

MULTIPART_RESOLVER_ATTRIBUTE

public static final String MULTIPART_RESOLVER_ATTRIBUTE

Request attribute to hold current multipart resolver, retrievable by views/binders.

See Also:: RequestContextUtils.getMultipartResolver(javax.servlet.ServletRequest)

LOCALE_RESOLVER_ATTRIBUTE

public static final String LOCALE_RESOLVER_ATTRIBUTE

Request attribute to hold current locale, retrievable by views.

See Also:: RequestContextUtils.getLocaleResolver(javax.servlet.http.HttpServletRequest)

THEME_RESOLVER_ATTRIBUTE

public static final String THEME_RESOLVER_ATTRIBUTE

Request attribute to hold current theme, retrievable by views.

See Also:: RequestContextUtils.getThemeResolver(javax.servlet.http.HttpServletRequest)

PAGE_NOT_FOUND_LOG_CATEGORY

public static final String PAGE_NOT_FOUND_LOG_CATEGORY

Log category to use when no mapped handler is found for a request.

See Also:: Constant Field Values

pageNotFoundLogger

protected static final Log pageNotFoundLogger

Additional logger to use when no mapped handler is found for a request.

Constructor Detail

DispatcherServlet

public DispatcherServlet()

Method Detail

setCleanupAfterInclude

public void setCleanupAfterInclude(boolean cleanupAfterInclude)

Set whether to perform cleanup of request attributes after an include request, i.e. whether to reset the original state of all request attributes after the DispatcherServlet has processed within an include request. Else, just the DispatcherServlet's own request attributes will be reset, but not model attributes for JSPs or special attributes set by views (for example, JSTL's).

Default is true, which is strongly recommended. Views should not rely on request attributes having been set by (dynamic) includes. This allows JSP views rendered by an included controller to use any model attributes, even with the same names as in the main JSP, without causing side effects. Only turn this off for special needs, for example to deliberately allow main JSPs to access attributes from JSP views rendered by an included controller.

setDetectAllHandlerMappings

public void setDetectAllHandlerMappings(boolean detectAllHandlerMappings)

Set whether to detect all HandlerMapping beans in this servlet's context. Else, just a single bean with name "handlerMapping" will be expected.

Default is true. Turn this off if you want this servlet to use a single HandlerMapping, despite multiple HandlerMapping beans being defined in the context.

setDetectAllHandlerExceptionResolvers

public void setDetectAllHandlerExceptionResolvers(boolean detectAllHandlerExceptionResolvers)

Set whether to detect all HandlerExceptionResolver beans in this servlet's context. Else, just a single bean with name "handlerExceptionResolver" will be expected.

Default is true. Turn this off if you want this servlet to use a single HandlerExceptionResolver, despite multiple HandlerExceptionResolver beans being defined in the context.

setDetectAllViewResolvers

public void setDetectAllViewResolvers(boolean detectAllViewResolvers)

Set whether to detect all ViewResolver beans in this servlet's context. Else, just a single bean with name "viewResolver" will be expected.

Default is true. Turn this off if you want this servlet to use a single ViewResolver, despite multiple ViewResolver beans being defined in the context.

initFrameworkServlet

protected void initFrameworkServlet()
                             throws ServletException,
                                    BeansException

Overridden method, invoked after any bean properties have been set and the WebApplicationContext and BeanFactory for this namespace is available.

Loads HandlerMapping and HandlerAdapter objects, and configures a ViewResolver and a LocaleResolver.

Overrides:: initFrameworkServlet in class FrameworkServlet

Throws:: BeansException - if thrown by ApplicationContext methods; ServletException - in case of an initialization exception

getDefaultStrategy

protected Object getDefaultStrategy(Class strategyInterface)
                             throws BeansException

Return the default strategy object for the given strategy interface.

Default implementation delegates to getDefaultStrategies, expecting a single object in the list.

Parameters:: strategyInterface - the strategy interface
Returns:: the corresponding strategy object
Throws:: BeansException - if initialization failed
See Also:: getDefaultStrategies(java.lang.Class)

getDefaultStrategies

protected List getDefaultStrategies(Class strategyInterface)
                             throws BeansException

Create a List of default strategy objects for the given strategy interface.

The default implementation uses the "DispatcherServlet.properties" file (in the same package as the DispatcherServlet class) to determine the class names. It instantiates the strategy objects and satisifies ApplicationContextAware if necessary.

Parameters:: strategyInterface - the strategy interface
Returns:: the List of corresponding strategy objects
Throws:: BeansException - if initialization failed

doService

protected void doService(HttpServletRequest request,
                         HttpServletResponse response)
                  throws Exception

Expose the DispatcherServlet-specific request attributes and delegate to doDispatch for the actual dispatching.

Specified by:: doService in class FrameworkServlet

Parameters:: request - current HTTP request; response - current HTTP response
Throws:: Exception - in case of any kind of processing failure
See Also:: doDispatch(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)

doDispatch

protected void doDispatch(HttpServletRequest request,
                          HttpServletResponse response)
                   throws Exception

Process the actual dispatching to the handler.

The handler will be obtained by applying the servlet's HandlerMappings in order. The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters to find the first that supports the handler class.

All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers themselves to decide which methods are acceptable.

Parameters:: request - current HTTP request; response - current HTTP response
Throws:: Exception - in case of any kind of processing failure

getLastModified

protected long getLastModified(HttpServletRequest request)

Override HttpServlet's getLastModified method to evaluate the Last-Modified value of the mapped handler.

checkMultipart

protected HttpServletRequest checkMultipart(HttpServletRequest request)
                                     throws MultipartException

Convert the request into a multipart request, and make multipart resolver available. If no multipart resolver is set, simply use the existing request.

Parameters:: request - current HTTP request
Returns:: the processed request (multipart wrapper if necessary)
Throws:: MultipartException

getHandler

protected HandlerExecutionChain getHandler(HttpServletRequest request,
                                           boolean cache)
                                    throws Exception

Return the HandlerExecutionChain for this request. Try all handler mappings in order.

Parameters:: request - current HTTP request; cache - whether to cache the HandlerExecutionChain in a request attribute
Returns:: the HandlerExceutionChain, or null if no handler could be found
Throws:: Exception

noHandlerFound

protected void noHandlerFound(HttpServletRequest request,
                              HttpServletResponse response)
                       throws IOException

No handler found -> set appropriate HTTP response status.

Parameters:: request - current HTTP request; response - current HTTP response
Throws:: IOException - if thrown by the HttpServletResponse

getHandlerAdapter

protected HandlerAdapter getHandlerAdapter(Object handler)
                                    throws ServletException

Return the HandlerAdapter for this handler object.

Parameters:: handler - the handler object to find an adapter for
Throws:: ServletException - if no HandlerAdapter can be found for the handler. This is a fatal error.

processHandlerException

protected ModelAndView processHandlerException(HttpServletRequest request,
                                               HttpServletResponse response,
                                               Object handler,
                                               Exception ex)
                                        throws Exception

Determine an error ModelAndView via the registered HandlerExceptionResolvers.

Parameters:: request - current HTTP request; response - current HTTP response; handler - the executed handler, or null if none chosen at the time of the exception (for example, if multipart resolution failed); ex - the exception that got thrown during handler execution
Returns:: a corresponding ModelAndView to forward to
Throws:: Exception - if no error ModelAndView found

render

protected void render(ModelAndView mv,
                      HttpServletRequest request,
                      HttpServletResponse response)
               throws Exception

Render the given ModelAndView. This is the last stage in handling a request. It may involve resolving the view by name.

Parameters:: mv - the ModelAndView to render; request - current HTTP servlet request; response - current HTTP servlet response
Throws:: Exception - if there's a problem rendering the view

resolveViewName

protected View resolveViewName(String viewName,
                               Map model,
                               Locale locale,
                               HttpServletRequest request)
                        throws Exception

Resolve the given view name into a View object (to be rendered).

Default implementations asks all ViewResolvers of this dispatcher. Can be overridden for custom resolution strategies, potentially based on specific model attributes or request parameters.

Parameters:: viewName - the name of the view to resolve; model - the model to be passed to the view; locale - the current locale; request - current HTTP servlet request
Returns:: the View object, or null if none found
Throws:: Exception - if the view cannot be resolved (typically in case of problems creating an actual View object)
See Also:: ViewResolver.resolveViewName(java.lang.String, java.util.Locale)