spring mvc DispatcherServlet详解之前传---FrameworkServlet
2016-03-29 17:50
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springmvcDispatcherServlet详解之前传---FrameworkServlet
做项目时碰到Controller不能使用aop进行拦截，从网上搜索得知：使用springmvc启动了两个context：applicationContext和WebapplicationContext。首先我们来了解applicationContext和WebapplicationContext区别和联系吧
1.ApplicationContext和WebApplicationContext是继承关系
/**
*Interfacetoprovideconfigurationforawebapplication.Thisisread-onlywhile
*theapplicationisrunning,butmaybereloadediftheimplementationsupportsthis.
*
*<p>Thisinterfaceaddsa{@codegetServletContext()}methodtothegeneric
*ApplicationContextinterface,anddefinesawell-knownapplicationattributename
*thattherootcontextmustbeboundtointhebootstrapprocess.
*
*<p>Likegenericapplicationcontexts,webapplicationcontextsarehierarchical.
*Thereisasinglerootcontextperapplication,whileeachservletintheapplication
*(includingadispatcherservletintheMVCframework)hasitsownchildcontext.
*
*<p>Inadditiontostandardapplicationcontextlifecyclecapabilities,
*WebApplicationContextimplementationsneedtodetect{@linkServletContextAware}
*beansandinvokethe{@codesetServletContext}methodaccordingly.*/
publicinterfaceWebApplicationContextextendsApplicationContext{2.ContextLoaderListener创建基于web的应用根applicationContext并将它放入到ServletContext.
applicationContext加载或者卸载spring管理的beans。在structs和springmvc的控制层都是这样使用的。
3.DispatcherServlet创建自己的WebApplicationContext并管理这个WebApplicationContext里面的handlers/controllers/view-resolvers.
4.当ContextLoaderListener和DispatcherServlet一起使用时,ContextLoaderListener先创建一个根applicationContext，然后DispatcherSerlvet创建一个子applicationContext并且绑定到根applicationContext。
首先来看看web.xml的定义：
一般的web应用，通过ContextLoaderListener监听，ContextLoaderListener中加载的context成功后，spring将applicationContext存放在ServletContext中key值为"org.springframework.web.context.WebApplicationContext.ROOT"的attribute中。
<listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <context-param> <param-name>contextConfigLocation</param-name> <param-value>classpath*:conf/applicationContext*.xml</param-value> </context-param>
DispatcherServlet加载的context成功后，会将applicationContext存放在org.springframework.web.servlet.FrameworkServlet.CONTEXT.+(servletName)的attribute中。
<servlet> <servlet-name>mvcServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath:conf/spring-dispatcher-servlet.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet>
当然，如果没有指定*servlet.xml配置，则默认使用DispatcherServlet的默认配置DispatcherServlet.properties
#DefaultimplementationclassesforDispatcherServlet'sstrategyinterfaces. #UsedasfallbackwhennomatchingbeansarefoundintheDispatcherServletcontext. #Notmeanttobecustomizedbyapplicationdevelopers. org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\ org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\ org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\ org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\ org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\ org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager
简单的来说：springbean的管理在applicationContext中，ContextLoaderListener的作用：
1.将applicationContext的生命周期和servletContext的生命周期联系到一起。
2.自动管理applicationContext的创建，ContextLoaderListener给我们提供了一个便利，不用显式的去创建applicationContext。
DispatcherServlet相关bean的管理在
WebApplicationContext，ServletContextListener创建WebApplicationContext，WebApplicationContext可以访问
ServletContext/ServletContextAware这些bean，还可以访问getServletContext方法。
正式的官方文档：
AwebapplicationcandefineanynumberofDispatcherServlets.Eachservletwilloperateinitsownnamespace,loadingitsownapplicationcontextwithmappings,handlers,etc.OnlytherootapplicationcontextasloadedbyContextLoaderListener,ifany,willbeshared. AsofSpring3.1,DispatcherServletmaynowbeinjectedwithawebapplicationcontext,ratherthancreatingitsowninternally.ThisisusefulinServlet3.0+environments,whichsupportprogrammaticregistrationofservletinstances.
在一个web应用中使用多个DispatcherServlet，每个servlet通过自己的命名空间来获取自己的webapplicationContext，然后加载此applicationContext里面的hangdlerMapping，hangdlerAdapter等等。ContextLoaderListener加载根application，所有子applicationContext共享根applicationContext。
从版本3.1后，spring支持将DispatcherServlet注入到根applicationContext，而不用创建自己的webapplicationContext，这主要为支持servlet3.0以上版本环境的要求，因为servlet3.0以上版本支持使用编程的方式来注册servlet实例。
spring支持使用多层层次applicationContext，通常我们使用两层结构就够了。
接下来，通过深入源代码层来探究WebApplicationContext是如何创建的？
1.DispatcherServlet的初始化过程使用到applicationContext。
我们知道DispatcherServlet直接继承自FrameworkServlet，而FrameworkServlet又继承了HttpServletBean和ApplicationContextAware。
2.FrameworkServlet实现了ApplicationContextAware接口的setApplicationContext()方法，可知DispatcherServlet的applicationContext来自FrameworkServlet。
/**
*CalledbySpringvia{@linkApplicationContextAware}toinjectthecurrent
*applicationcontext.ThismethodallowsFrameworkServletstoberegisteredas
*Springbeansinsideanexisting{@linkWebApplicationContext}ratherthan
*{@link#findWebApplicationContext()finding}a
*{@linkorg.springframework.web.context.ContextLoaderListenerbootstrapped}context.
*<p>Primarilyaddedtosupportuseinembeddedservletcontainers.
*@since4.0
*/
@Override
publicvoidsetApplicationContext(ApplicationContextapplicationContext){
if(this.webApplicationContext==null&&applicationContextinstanceofWebApplicationContext){
this.webApplicationContext=(WebApplicationContext)applicationContext;
this.webApplicationContextInjected=true;
}
}3.FrameworkServlet的setApplicationContext()方法中WebApplicationContext是如何实例化的呢？
FrameworkServlet继承自HttpServletBean，HttpServletBean的初始化方法：
/**
*Mapconfigparametersontobeanpropertiesofthisservlet,and
*invokesubclassinitialization.
*@throwsServletExceptionifbeanpropertiesareinvalid(orrequired
*propertiesaremissing),orifsubclassinitializationfails.
*/
@Override
publicfinalvoidinit()throwsServletException{
if(logger.isDebugEnabled()){
logger.debug("Initializingservlet'"+getServletName()+"'");
}
//Setbeanpropertiesfrominitparameters.
try{
PropertyValuespvs=newServletConfigPropertyValues(getServletConfig(),this.requiredProperties);
BeanWrapperbw=PropertyAccessorFactory.forBeanPropertyAccess(this);
ResourceLoaderresourceLoader=newServletContextResourceLoader(getServletContext());
bw.registerCustomEditor(Resource.class,newResourceEditor(resourceLoader,getEnvironment()));
initBeanWrapper(bw);
bw.setPropertyValues(pvs,true);
}
catch(BeansExceptionex){
logger.error("Failedtosetbeanpropertiesonservlet'"+getServletName()+"'",ex);
throwex;
}
//Letsubclassesdowhateverinitializationtheylike.
initServletBean();
if(logger.isDebugEnabled()){
logger.debug("Servlet'"+getServletName()+"'configuredsuccessfully");
}
}FrameworkServlet实现了initServletBean();
/**
*Overriddenmethodof{@linkHttpServletBean},invokedafteranybeanproperties
*havebeenset.Createsthisservlet'sWebApplicationContext.
*/
@Override
protectedfinalvoidinitServletBean()throwsServletException{
getServletContext().log("InitializingSpringFrameworkServlet'"+getServletName()+"'");
if(this.logger.isInfoEnabled()){
this.logger.info("FrameworkServlet'"+getServletName()+"':initializationstarted");
}
longstartTime=System.currentTimeMillis();
try{
this.webApplicationContext=initWebApplicationContext();
initFrameworkServlet();
}
catch(ServletExceptionex){
this.logger.error("Contextinitializationfailed",ex);
throwex;
}
catch(RuntimeExceptionex){
this.logger.error("Contextinitializationfailed",ex);
throwex;
}
if(this.logger.isInfoEnabled()){
longelapsedTime=System.currentTimeMillis()-startTime;
this.logger.info("FrameworkServlet'"+getServletName()+"':initializationcompletedin"+
elapsedTime+"ms");
}
}最终追踪到FrameworkServlet的initWebApplicationContext()方法
/**
*InitializeandpublishtheWebApplicationContextforthisservlet.
*<p>Delegatesto{@link#createWebApplicationContext}foractualcreation
*ofthecontext.Canbeoverriddeninsubclasses.
*@returntheWebApplicationContextinstance
*@see#FrameworkServlet(WebApplicationContext)
*@see#setContextClass
*@see#setContextConfigLocation
*/
protectedWebApplicationContextinitWebApplicationContext(){
WebApplicationContextrootContext=
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
WebApplicationContextwac=null;
if(this.webApplicationContext!=null){
//Acontextinstancewasinjectedatconstructiontime->useit
wac=this.webApplicationContext;
if(wacinstanceofConfigurableWebApplicationContext){
ConfigurableWebApplicationContextcwac=(ConfigurableWebApplicationContext)wac;
if(!cwac.isActive()){
//Thecontexthasnotyetbeenrefreshed->provideservicessuchas
//settingtheparentcontext,settingtheapplicationcontextid,etc
if(cwac.getParent()==null){
//Thecontextinstancewasinjectedwithoutanexplicitparent->set
//therootapplicationcontext(ifany;maybenull)astheparent
cwac.setParent(rootContext);
}
configureAndRefreshWebApplicationContext(cwac);
}
}
}
if(wac==null){
//Nocontextinstancewasinjectedatconstructiontime->seeifone
//hasbeenregisteredintheservletcontext.Ifoneexists,itisassumed
//thattheparentcontext(ifany)hasalreadybeensetandthatthe
//userhasperformedanyinitializationsuchassettingthecontextid
wac=findWebApplicationContext();
}
if(wac==null){
//Nocontextinstanceisdefinedforthisservlet->createalocalone
wac=createWebApplicationContext(rootContext);
}
if(!this.refreshEventReceived){
//EitherthecontextisnotaConfigurableApplicationContextwithrefresh
//supportorthecontextinjectedatconstructiontimehadalreadybeen
//refreshed->triggerinitialonRefreshmanuallyhere.
onRefresh(wac);
}
if(this.publishContext){
//Publishthecontextasaservletcontextattribute.
StringattrName=getServletContextAttributeName();
getServletContext().setAttribute(attrName,wac);
if(this.logger.isDebugEnabled()){
this.logger.debug("PublishedWebApplicationContextofservlet'"+getServletName()+
"'asServletContextattributewithname["+attrName+"]");
}
}
returnwac;
}我们来分析整个流程吧：
1.获取根applicationContext。
WebApplicationContextrootContext=
WebApplicationContextUtils.getWebApplicationContext(getServletContext());
/**
*Findtheroot{@linkWebApplicationContext}forthiswebapp,typically
*loadedvia{@linkorg.springframework.web.context.ContextLoaderListener}.
*<p>Willrethrowanexceptionthathappenedonrootcontextstartup,
*todifferentiatebetweenafailedcontextstartupandnocontextatall.
*@paramscServletContexttofindthewebapplicationcontextfor
*@returntherootWebApplicationContextforthiswebapp,or{@codenull}ifnone
*@seeorg.springframework.web.context.WebApplicationContext#ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE
*/
publicstaticWebApplicationContextgetWebApplicationContext(ServletContextsc){
returngetWebApplicationContext(sc,WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);
}
/**
*Findacustom{@linkWebApplicationContext}forthiswebapp.
*@paramscServletContexttofindthewebapplicationcontextfor
*@paramattrNamethenameoftheServletContextattributetolookfor
*@returnthedesiredWebApplicationContextforthiswebapp,or{@codenull}ifnone
*/
publicstaticWebApplicationContextgetWebApplicationContext(ServletContextsc,StringattrName){
Assert.notNull(sc,"ServletContextmustnotbenull");
Objectattr=sc.getAttribute(attrName);
if(attr==null){
returnnull;
}
if(attrinstanceofRuntimeException){
throw(RuntimeException)attr;
}
if(attrinstanceofError){
throw(Error)attr;
}
if(attrinstanceofException){
thrownewIllegalStateException((Exception)attr);
}
if(!(attrinstanceofWebApplicationContext)){
thrownewIllegalStateException("ContextattributeisnotoftypeWebApplicationContext:"+attr);
}
return(WebApplicationContext)attr;
}2.判断webapplicationContext是否存在？存在的话就重利用该webapplicationContext
protectedvoidconfigureAndRefreshWebApplicationContext(ConfigurableWebApplicationContextwac){
if(ObjectUtils.identityToString(wac).equals(wac.getId())){
//Theapplicationcontextidisstillsettoitsoriginaldefaultvalue
//->assignamoreusefulidbasedonavailableinformation
if(this.contextId!=null){
wac.setId(this.contextId);
}
else{
//Generatedefaultid...
wac.setId(ConfigurableWebApplicationContext.APPLICATION_CONTEXT_ID_PREFIX+
ObjectUtils.getDisplayString(getServletContext().getContextPath())+"/"+getServletName());
}
}
wac.setServletContext(getServletContext());
wac.setServletConfig(getServletConfig());
wac.setNamespace(getNamespace());
wac.addApplicationListener(newSourceFilteringListener(wac,newContextRefreshListener()));
//Thewacenvironment's#initPropertySourceswillbecalledinanycasewhenthecontext
//isrefreshed;doiteagerlyheretoensureservletpropertysourcesareinplacefor
//useinanypost-processingorinitializationthatoccursbelowpriorto#refresh
ConfigurableEnvironmentenv=wac.getEnvironment();
if(envinstanceofConfigurableWebEnvironment){
((ConfigurableWebEnvironment)env).initPropertySources(getServletContext(),getServletConfig());
}
postProcessWebApplicationContext(wac);
applyInitializers(wac);
wac.refresh();
}不存在的话，根据配置的属性名去查询：
/**
*Retrievea{@codeWebApplicationContext}fromthe{@codeServletContext}
*attributewiththe{@link#setContextAttributeconfiguredname}.The
*{@codeWebApplicationContext}musthavealreadybeenloadedandstoredinthe
*{@codeServletContext}beforethisservletgetsinitialized(orinvoked).
*<p>Subclassesmayoverridethismethodtoprovideadifferent
*{@codeWebApplicationContext}retrievalstrategy.
*@returntheWebApplicationContextforthisservlet,or{@codenull}ifnotfound
*@see#getContextAttribute()
*/
protectedWebApplicationContextfindWebApplicationContext(){
StringattrName=getContextAttribute();
if(attrName==null){
returnnull;
}
WebApplicationContextwac=
WebApplicationContextUtils.getWebApplicationContext(getServletContext(),attrName);
if(wac==null){
thrownewIllegalStateException("NoWebApplicationContextfound:initializernotregistered?");
}
returnwac;
}3.如果还查询不到WebapplicationContext，那么就创建一个新的WebapplicationContext，并绑定到rootWebapplicationContext上：
/**
*InstantiatetheWebApplicationContextforthisservlet,eitheradefault
*{@linkorg.springframework.web.context.support.XmlWebApplicationContext}
*ora{@link#setContextClasscustomcontextclass},ifset.
*<p>Thisimplementationexpectscustomcontextstoimplementthe
*{@linkorg.springframework.web.context.ConfigurableWebApplicationContext}
*interface.Canbeoverriddeninsubclasses.
*<p>Donotforgettoregisterthisservletinstanceasapplicationlisteneronthe
*createdcontext(fortriggeringits{@link#onRefreshcallback},andtocall
*{@linkorg.springframework.context.ConfigurableApplicationContext#refresh()}
*beforereturningthecontextinstance.
*@paramparenttheparentApplicationContexttouse,or{@codenull}ifnone
*@returntheWebApplicationContextforthisservlet
*@seeorg.springframework.web.context.support.XmlWebApplicationContext
*/
protectedWebApplicationContextcreateWebApplicationContext(ApplicationContextparent){
Class<?>contextClass=getContextClass();
if(this.logger.isDebugEnabled()){
this.logger.debug("Servletwithname'"+getServletName()+
"'willtrytocreatecustomWebApplicationContextcontextofclass'"+
contextClass.getName()+"'"+",usingparentcontext["+parent+"]");
}
if(!ConfigurableWebApplicationContext.class.isAssignableFrom(contextClass)){
thrownewApplicationContextException(
"Fatalinitializationerrorinservletwithname'"+getServletName()+
"':customWebApplicationContextclass["+contextClass.getName()+
"]isnotoftypeConfigurableWebApplicationContext");
}
ConfigurableWebApplicationContextwac=
(ConfigurableWebApplicationContext)BeanUtils.instantiateClass(contextClass);
wac.setEnvironment(getEnvironment());
wac.setParent(parent);
wac.setConfigLocation(getContextConfigLocation());
configureAndRefreshWebApplicationContext(wac);
returnwac;
}4.将子applicationContext发布到servletcontext上。
if(this.publishContext){
//Publishthecontextasaservletcontextattribute.
StringattrName=getServletContextAttributeName();
getServletContext().setAttribute(attrName,wac);
if(this.logger.isDebugEnabled()){
this.logger.debug("PublishedWebApplicationContextofservlet'"+getServletName()+
"'asServletContextattributewithname["+attrName+"]");
}
}/**
*ReturntheServletContextattributenameforthisservlet'sWebApplicationContext.
*<p>Thedefaultimplementationreturns
*{@codeSERVLET_CONTEXT_PREFIX+servletname}.
*@see#SERVLET_CONTEXT_PREFIX
*@see#getServletName
*/
publicStringgetServletContextAttributeName(){
returnSERVLET_CONTEXT_PREFIX+getServletName();
}
/**
*PrefixfortheServletContextattributefortheWebApplicationContext.
*Thecompletionistheservletname.
*/
publicstaticfinalStringSERVLET_CONTEXT_PREFIX=FrameworkServlet.class.getName()+".CONTEXT.";
最后，ContextLoaderListener启动时如何产生applicationContext呢？
见参考我的这篇文章：
小结：
我们就以FrameworkServlet的官方说明来结束吧。没有比它更合适的！希望你喜欢。
publicabstractclassFrameworkServlet
extendsHttpServletBean
implementsApplicationContextAwareBaseservletforSpring'swebframework.ProvidesintegrationwithaSpringapplicationcontext,inaJavaBean-basedoverallsolution.
Thisclassoffersthefollowingfunctionality:
ManagesaWebApplicationContextinstanceperservlet.Theservlet'sconfigurationisdeterminedbybeansintheservlet'snamespace.
Publisheseventsonrequestprocessing,whetherornotarequestissuccessfullyhandled.
SubclassesmustimplementdoService(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)tohandlerequests.BecausethisextendsHttpServletBeanratherthanHttpServletdirectly,beanpropertiesareautomaticallymappedontoit.SubclassescanoverrideinitFrameworkServlet()forcustominitialization.
Detectsa"contextClass"parameterattheservletinit-paramlevel,fallingbacktothedefaultcontextclass,XmlWebApplicationContext,ifnotfound.Notethat,withthedefaultFrameworkServlet,acustomcontextclassneedstoimplementtheConfigurableWebApplicationContextSPI.
Acceptsanoptional"contextInitializerClasses"servletinit-paramthatspecifiesoneormoreApplicationContextInitializerclasses.Themanagedwebapplicationcontextwillbedelegatedtotheseinitializers,allowingforadditionalprogrammaticconfiguration,e.g.addingpropertysourcesoractivatingprofilesagainstthecontext'senvironment.SeealsoContextLoaderwhichsupportsa"contextInitializerClasses"context-paramwithidenticalsemanticsforthe"root"webapplicationcontext.
Passesa"contextConfigLocation"servletinit-paramtothecontextinstance,parsingitintopotentiallymultiplefilepathswhichcanbeseparatedbyanynumberofcommasandspaces,like"test-servlet.xml,myServlet.xml".Ifnotexplicitlyspecified,thecontextimplementationissupposedtobuildadefaultlocationfromthenamespaceoftheservlet.
Note:Incaseofmultipleconfiglocations,laterbeandefinitionswilloverrideonesdefinedinearlierloadedfiles,atleastwhenusingSpring'sdefaultApplicationContextimplementation.ThiscanbeleveragedtodeliberatelyoverridecertainbeandefinitionsviaanextraXMLfile.
Thedefaultnamespaceis"'servlet-name'-servlet",e.g."test-servlet"foraservlet-name"test"(leadingtoa"/WEB-INF/test-servlet.xml"defaultlocationwithXmlWebApplicationContext).Thenamespacecanalsobesetexplicitlyviathe"namespace"servletinit-param.
AsofSpring3.1,FrameworkServletmaynowbeinjectedwithawebapplicationcontext,ratherthancreatingitsowninternally.ThisisusefulinServlet3.0+environments,whichsupportprogrammaticregistrationofservletinstances.SeeFrameworkServlet(WebApplicationContext)Javadocfordetails.
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