spring与其它框架集成

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Chapter14.Integratingwithotherwebframeworks
14.1.Introduction

SpringcanbeeasilyintegratedintoanyJava-basedwebframework.AllyouneedtodoistodeclaretheContextLoaderListenerinyourweb.xmlanduseacontextConfigLocation<context-param>tosetwhichcontextfilestoload.
The<context-param>:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/applicationContext*.xml</param-value>
</context-param>
The<listener>:
<listener>

<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

NOTE:ListenerswereaddedtotheServletAPIinversion2.3.IfyouhaveaServlet2.2container,youcanusetheContextLoaderServlettoachievethissamefunctionality.

Ifyoudon'tspecifythecontextConfigLocationcontextparameter,theContextLoaderListenerwilllookfora/WEB-INF/applicationContext.xmlfiletoload.Oncethecontextfilesareloaded,SpringcreatesaWebApplicationContextobjectbasedonthebeandefinitionsandputsitintotheServletContext.

AllJavawebframeworksarebuiltontopoftheServletAPI,soyoucanusethefollowingcodetogettheApplicationContextthatSpringcreated.
WebApplicationContextctx=WebApplicationContextUtils.getWebApplicationContext(servletContext);

TheWebApplicationContextUtilsclassisforconvenience,soyoudon'thavetorememberthenameoftheServletContextattribute.ItsgetWebApplicationContext()methodwillreturnnullifanobjectdoesn'texistundertheWebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTEkey.RatherthanriskgettingNullPointerExceptionsinyourapplication,it'sbettertousethegetRequiredWebApplicationContext()method.ThismethodthrowsanExceptionwhentheApplicationContextismissing.
OnceyouhaveareferencetotheWebApplicationContext,youcanretrievebeansbytheirnameortype.Mostdevelopersretrievebeansbyname,thencastthemtooneoftheirimplementedinterfaces.

Fortunately,mostoftheframeworksinthissectionhavesimplerwaysoflookingupbeans.NotonlydotheymakeiteasytogetbeansfromtheBeanFactory,buttheyalsoallowyoutousedependencyinjectionontheircontrollers.Eachframeworksectionhasmoredetailonitsspecificintegrationstrategies.
14.2.JavaServerFaces

JavaServerFaces(JSF)isacomponent-based,event-drivenwebframework.AccordingtoSunMicrosystem'sJSFOverview,JSFtechnologyincludes:

AsetofAPIsforrepresentingUIcomponentsandmanagingtheirstate,handlingeventsandinputvalidation,definingpagenavigation,andsupportinginternationalizationandaccessibility.

AJavaServerPages(JSP)customtaglibraryforexpressingaJavaServerFacesinterfacewithinaJSPpage.
14.2.1.DelegatingVariableResolver

TheeasiestwaytointegrateyourSpringmiddle-tierwithyourJSFweblayeristousetheDelegatingVariableResolverclass.Toconfigurethisvariableresolverinyourapplication,you'llneedtoedityourfaces-context.xml.Aftertheopening<faces-config>element,addan<application>elementanda<variable-resolver>elementwithinit.ThevalueofthevariableresolvershouldreferenceSpring'sDelegatingVariableResolver:
<faces-config>
<application>
<variable-resolver>org.springframework.web.jsf.DelegatingVariableResolver</variable-resolver>
<locale-config>

<default-locale>en</default-locale>
<supported-locale>en</supported-locale>
<supported-locale>es</supported-locale>
</locale-config>
<message-bundle>messages</message-bundle>
</application>

ByspecifyingSpring'svariableresolver,youcanconfigureSpringbeansasmanagedpropertiesofyourmanagedbeans.TheDelegatingVariableResolverwillfirstdelegatevaluelookupstothedefaultresolveroftheunderlyingJSFimplementation,andthentoSpring'srootWebApplicationContext.ThisallowsyoutoeasilyinjectdependenciesintoyourJSF-managedbeans.

Managedbeansaredefinedinyourfaces-config.xmlfile.Belowisanexamplewhere#{userManager}isabeanthat'sretrievedfromSpring'sBeanFactory.
<managed-bean>
<managed-bean-name>userList</managed-bean-name>

<managed-bean-class>com.whatever.jsf.UserList</managed-bean-class>
<managed-bean-scope>request</managed-bean-scope>
<managed-property>
<property-name>userManager</property-name>
<value>#{userManager}</value>
</managed-property>
</managed-bean>

TheDelegatingVariableResolveristherecommendedstrategyforintegratingJSFandSpring.Ifyou'relookingformorerobustintegrationfeatures,youmighttakealookattheJSF-Springproject.
14.2.2.FacesContextUtils

AcustomVariableResolverworkswellwhenmappingyourpropertiestobeansinfaces-config.xml,butattimesyoumayneedtogrababeanexplicitly.TheFacesContextUtilsclassmakesthiseasy.It'ssimilartoWebApplicationContextUtils,exceptthatittakesaFacesContextparameterratherthanaServletContextparameter.
ApplicationContextctx=FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
14.3.Struts

StrutsisthedefactowebframeworkforJavaapplications,mainlybecauseitwasoneofthefirsttobereleased(June2001).InventedbyCraigMcClanahan,StrutsisanopensourceprojecthostedbytheApacheSoftwareFoundation.Atthetime,itgreatlysimplifiedtheJSP/Servletprogrammingparadigmandwonovermanydeveloperswhowereusingproprietaryframeworks.Itsimplifiedtheprogrammingmodel,itwasopensource,andithadalargecommunity,whichallowedtheprojecttogrowandbecomepopularamongJavawebdevelopers.
TointegrateyourStrutsapplicationwithSpring,youhavetwooptions:

ConfigureSpringtomanageyourActionsasbeans,usingtheContextLoaderPlugin,andsettheirdependenciesinaSpringcontextfile.

SubclassSpring'sActionSupportclassesandgrabyourSpring-managedbeansexplicitlyusingagetWebApplicationContext()method.
14.3.1.ContextLoaderPlugin

TheContextLoaderPluginisaStruts1.1+plug-inthatloadsaSpringcontextfilefortheStrutsActionServlet.ThiscontextreferstotherootWebApplicationContext(loadedbytheContextLoaderListener)asitsparent.Thedefaultnameofthecontextfileisthenameofthemappedservlet,plus-servlet.xml.IfActionServletisdefinedinweb.xmlas<servlet-name>action</servlet-name>,thedefaultis/WEB-INF/action-servlet.xml.

Toconfigurethisplug-in,addthefollowingXMLtotheplug-inssectionnearthebottomofyourstruts-config.xmlfile:

<plug-inclassName="org.springframework.web.struts.ContextLoaderPlugIn"/>

Thelocationofthecontextconfigurationfilescanbecustomizedusingthe"contextConfigLocation"property.

<plug-inclassName="org.springframework.web.struts.ContextLoaderPlugIn">

<set-propertyproperty="contextConfigLocation"

value="/WEB-INF/action-servlet.xml.xml,/WEB-INF/applicationContext.xml"/>

</plug-in>

Itispossibletousethisplugintoloadallyourcontextfiles,whichcanbeusefulwhenusingtestingtoolslikeStrutsTestCase.StrutsTestCase'sMockStrutsTestCasewon'tinitializeListenersonstartupsoputtingallyourcontextfilesinthepluginisaworkaround.Abughasbeenfiledforthisissue.

Afterconfiguringthisplug-ininstruts-config.xml,youcanconfigureyourActiontobemanagedbySpring.Spring1.1.3providestwowaystodothis:

OverrideStruts'defaultRequestProcessorwithSpring'sDelegatingRequestProcessor.

UsetheDelegatingActionProxyclassinthetypeattributeofyour<action-mapping>.

BothofthesemethodsallowyoutomanageyourActionsandtheirdependenciesintheaction-context.xmlfile.ThebridgebetweentheActioninstruts-config.xmlandaction-servlet.xmlisbuiltwiththeaction-mapping's"path"andthebean's"name".Ifyouhavethefollowinginyourstruts-config.xmlfile:

<actionpath="/users".../>

YoumustdefinethatAction'sbeanwiththe"/users"nameinaction-servlet.xml:

<beanname="/users".../>
14.3.1.1.DelegatingRequestProcessor

ToconfiguretheDelegatingRequestProcessorinyourstruts-config.xmlfile,overridethe"processorClass"propertyinthe<controller>element.Theselinesfollowthe<action-mapping>element.
<controller>

<set-propertyproperty="processorClass"

value="org.springframework.web.struts.DelegatingRequestProcessor"/>
</controller>

Afteraddingthissetting,yourActionwillautomaticallybelookedupinSpring'scontextfile,nomatterwhatthetype.Infact,youdon'tevenneedtospecifyatype.Bothofthefollowingsnippetswillwork:

<actionpath="/user"type="com.whatever.struts.UserAction"/>

<actionpath="/user"/>

Ifyou'reusingStruts'modulesfeature,yourbeannamesmustcontainthemoduleprefix.Forexample,anactiondefinedas<actionpath="/user"/>withmoduleprefix"admin"requiresabeannamewith<beanname="/admin/user"/>.

NOTE:Ifyou'reusingTilesinyourStrutsapplication,youmustconfigureyour<controller>withtheDelegatingTilesRequestProcessor.
14.3.1.2.DelegatingActionProxy

IfyouhaveacustomRequestProcessorandcan'tusetheDelegatingTilesRequestProcessor,youcanusetheDelegatingActionProxyasthetypeinyouraction-mapping.

<actionpath="/user"type="org.springframework.web.struts.DelegatingActionProxy"

name="userForm"scope="request"validate="false"parameter="method">

<forwardname="list"path="/userList.jsp"/>

<forwardname="edit"path="/userForm.jsp"/>
</action>

Thebeandefinitioninaction-servlet.xmlremainsthesame,whetheryouuseacustomRequestProcessorortheDelegatingActionProxy.

IfyoudefineyourActioninacontextfile,thefullfeaturesetofSpring'sbeancontainerwillbeavailableforit:dependencyinjectionaswellastheoptiontoinstantiateanewActioninstanceforeachrequest.Toactivatethelatter,addsingleton="false"toyourAction'sbeandefinition.

<beanname="/user"singleton="false"autowire="byName"

class="org.example.web.UserAction"/>
14.3.2.ActionSupportClasses

Aspreviouslymentioned,youcanretrievetheWebApplicationContextfromtheServletContextusingtheWebApplicationContextUtilsclass.AneasierwayistoextendSpring'sActionclassesforStruts.Forexample,insteadofsubclassingStruts'Actionclass,youcansubclassSpring'sActionSupportclass.

TheActionSupportclassprovidesadditionalconveniencemethods,likegetWebApplicationContext().BelowisanexampleofhowyoumightusethisinanAction:

publicclassUserActionextendsDispatchActionSupport{

publicActionForwardexecute(ActionMappingmapping,
ActionFormform,
HttpServletRequestrequest,
HttpServletResponseresponse)
throwsException{

if(log.isDebugEnabled()){

log.debug("entering'delete'method...");
}
WebApplicationContextctx=getWebApplicationContext();

UserManagermgr=(UserManager)ctx.getBean("userManager");

//talktomanagerforbusinesslogic 

returnmapping.findForward("success");
}
}

SpringincludessubclassesforallofthestandardStrutsActions-theSpringversionsmerelyhaveSupportappendedtothename:
ActionSupport,
DispatchActionSupport,
LookupDispatchActionSupportand
MappingDispatchActionSupport.

Therecommendedstrategyistousetheapproachthatbestsuitsyourproject.Subclassingmakesyourcodemorereadable,andyouknowexactlyhowyourdependenciesareresolved.However,usingtheContextLoaderPluginallowyoutoeasilyaddnewdependenciesinyourcontextXMLfile.Eitherway,Springprovidessomeniceoptionsforintegratingthetwoframeworks.
14.4.Tapestry

Tapestryisapowerful,component-orientedwebapplicationframeworkfromApache'sJakartaproject(http://jakarta.apache.org/tapestry).WhileSpringhasitsownpowerfulwebuilayer,thereareanumberofuniqueadvantagestobuildingaJ2EEapplicationusingacombinationofTapestryforthewebui,andtheSpringcontainerforthelowerlayers.Thisdocumentattemptstodetailafewbestpracticesforcombiningthesetwoframeworks.ItisexpectedthatyouarerelativelyfamiliarwithbothTapestryandSpringFrameworkbasics,sotheywillnotbeexplainedhere.GeneralintroductorydocumentationforbothTapestryandSpringFrameworkareavailableontheirrespectivewebsites. 
14.4.1.Architecture

AtypicallayeredJ2EEapplicationbuiltwithTapestryandSpringwillconsistofatopUIlayerbuiltwithTapestry,andanumberoflowerlayers,hostedoutofoneormoreSpringApplicationContexts.
UserInterfaceLayer:

-concernedwiththeuserinterface
-containssomeapplicationlogic
-providedbyTapestry

-asidefromprovidingUIviaTapestry,codeinthislayerdoesitsworkviaobjectswhichimplementinterfacesfromtheServiceLayer.TheactualobjectswhichimplementtheseservicelayerinterfacesareobtainedfromaSpringApplicationContext.
ServiceLayer:

-applicationspecific'service'code

-workswithdomainobjects,andusestheMapperAPItogetthosedomainobjectsintoandoutofsomesortofrepository(database)

-hostedinoneormoreSpringcontexts

-codeinthislayermanipulatesobjectsinthedomainmodel,inanapplicationspecificfashion.Itdoesitsworkviaothercodeinthislayer,andviatheMapperAPI.Anobjectinthislayerisgiventhespecificmapperimplementationsitneedstoworkwith,viatheSpringcontext.

-sincecodeinthislayerishostedintheSpringcontext,itmaybetransactionallywrappedbytheSpringcontext,asopposedtomanagingitsowntransactions
DomainModel:

-domainspecificobjecthierarchy,whichdealswithdataandlogicspecifictothisdomain

-althoughthedomainobjecthierarchyisbuiltwiththeideathatitispersistedsomehowandmakessomegeneralconcessionstothis(forexample,bidirectionalrelationships),itgenerallyhasnoknowledgeofotherlayers.Assuch,itmaybetestedinisolation,andusedwithdifferentmappingimplementationsforproductionvs.testing.

-theseobjectsmaybestandalone,orusedinconjunctionwithaSpringapplicationcontexttotakeadvantageofsomeofthebenefitsofthecontext,e.g.,isolation,inversionofcontrol,differentstrategyimplementations,etc.
DataSourceLayer:
-MapperAPI(alsocalledDataAccessObjects):anAPIusedtopersistthedomainmodeltoarepositoryofsomesort(generallyaDB,butcouldbethefilesystem,memory,etc.)

-MapperAPIimplementations:oneormorespecificimplementationsoftheMapperAPI,forexample,aHibernate-specificmapper,aJDO-specificmapper,JDBC-specificmapper,oramemorymapper.

-mapperimplementationsliveinoneormoreSpringApplicationContexts.Aservicelayerobjectisgiventhemapperobjectsitneedstoworkwithviathecontext.
Database,filesystem,orotherrepositories:

-objectsinthedomainmodelarestoredintooneormorerepositoriesviaoneormoremapperimplementations

-arepositorymaybeverysimple(e.g.filesystem),ormayhaveitsownrepresentationofthedatafromthedomainmodel(i.e.aschemainadb).Itdoesnotknowaboutotherlayershowerver.
14.4.2.Implementation

Theonlyrealquestion(whichneedstobeaddressedbythisdocument),ishowTapestrypagesgetaccesstoserviceimplementations,whicharesimplybeansdefinedinaninstanceoftheSpringApplicationContext.
14.4.2.1.Sampleapplicationcontext

AssumewehavethefollowingsimpleApplicationContextdefinition,inxmlform:

<?xmlversion="1.0"encoding="UTF-8"?>

<!DOCTYPEbeansPUBLIC"-//SPRING//DTDBEAN//EN"

"http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<!--=========================GENERALDEFINITIONS=========================-->
<!--=========================PERSISTENCEDEFINITIONS=========================-->
<!--theDataSource-->

<beanid="dataSource"class="org.springframework.jndi.JndiObjectFactoryBean">

<propertyname="jndiName"><value>java:DefaultDS</value></property>

<propertyname="resourceRef"><value>false</value></property>
</bean>
<!--defineaHibernateSessionfactoryviaaSpringLocalSessionFactoryBean-->

<beanid="hibSessionFactory"

class="org.springframework.orm.hibernate.LocalSessionFactoryBean">

<propertyname="dataSource"><refbean="dataSource"/></property>
</bean>
<!--

-Definesatransactionmanagerforusageinbusinessordataaccessobjects.

-Nospecialtreatmentbythecontext,justabeaninstanceavailableasreference

-forbusinessobjectsthatwanttohandletransactions,e.g.viaTransactionTemplate.
-->

<beanid="transactionManager"

class="org.springframework.transaction.jta.JtaTransactionManager">
</bean>

<beanid="mapper"

class="com.whatever.dataaccess.mapper.hibernate.MapperImpl">

<propertyname="sessionFactory"><refbean="hibSessionFactory"/></property>
</bean>
<!--=========================BUSINESSDEFINITIONS=========================-->
<!--AuthenticationService,includingtxinterceptor-->

<beanid="authenticationServiceTarget"

class="com.whatever.services.service.user.AuthenticationServiceImpl">

<propertyname="mapper"><refbean="mapper"/></property>
</bean>

<beanid="authenticationService"

class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">

<propertyname="transactionManager"><refbean="transactionManager"/></property>

<propertyname="target"><refbean="authenticationServiceTarget"/></property>

<propertyname="proxyInterfacesOnly"><value>true</value></property>

<propertyname="transactionAttributes">
<props>

<propkey="*">PROPAGATION_REQUIRED</prop>
</props>
</property>
</bean>
<!--UserService,includingtxinterceptor-->

<beanid="userServiceTarget"

class="com.whatever.services.service.user.UserServiceImpl">

<propertyname="mapper"><refbean="mapper"/></property>
</bean>

<beanid="userService"

class="org.springframework.transaction.interceptor.TransactionProxyFactoryBean">

<propertyname="transactionManager"><refbean="transactionManager"/></property>

<propertyname="target"><refbean="userServiceTarget"/></property>

<propertyname="proxyInterfacesOnly"><value>true</value></property>

<propertyname="transactionAttributes">
<props>

<propkey="*">PROPAGATION_REQUIRED</prop>
</props>
</property>
</bean>
</beans>

InsidetheTapestryapplication,weneedtoloadthisapplicationcontext,andallowTapestrypagestogettheauthenticationServiceanduserServicebeans,whichimplementtheAuthenticationServiceandUserServiceinterfaces,respectively.

14.4.2.2.ObtainingbeansinTapestrypages

Atthispoint,theapplicationcontextisavailabletoawebapplicationbycallingSpring'sstaticutilityfunctionWebApplicationContextUtils.getApplicationContext(servletContext),whereservletContextisthestandardServletContextfromtheJ2EEServletspecification.Assuch,onesimplemechanismforapagetogetaninstanceoftheUserService,forexample,wouldbewithcodesuchas:
WebApplicationContextappContext=WebApplicationContextUtils.getApplicationContext(
getRequestCycle().getRequestContext().getServlet().getServletContext());

UserServiceuserService=(UserService)appContext.getBean("userService");
...somecodewhichusesUserService

Thismechanismdoeswork.Itcanbemadealotlessverbosebyencapsulatingmostofthefunctionalityinamethodinthebaseclassforthepageorcomponent.However,insomerespectsitgoesagainsttheInversionofControlapproachwhichSpringencourages,whichisbeingusedinotherlayersofthisapp,inthatideallyyouwouldlikethepagetonothavetoaskthecontextforaspecificbeanbyname,andinfact,thepagewouldideallynotknowaboutthecontextatall.

Luckily,thereisamechanismtoallowthis.WerelyuponthefactthatTapestryalreadyhasamechanismtodeclarativelyaddpropertiestoapage,anditisinfactthepreferredapproachtomanageallpropertiesonapageinthisdeclarativefashion,sothatTapestrycanproperlymanagetheirlifecycleaspartofthepageandcomponentlifecycle.
14.4.2.3.ExposingtheapplicationcontexttoTapestry

FirstweneedtomaketheApplicationContextavailabletotheTapestrypageorComponentwithouthavingtohavetheServletContext;thisisbecauseatthestageinthepage's/component'slifecyclewhenweneedtoaccesstheApplicationContext,theServletContextwon'tbeeasilyavailabletothepage,sowecan'tuseWebApplicationContextUtils.getApplicationContext(servletContext)directly.OnewayisbydefiningacustomversionoftheTapestryIEnginewhichexposesthisforus:
packagecom.whatever.web.xportal;
...
import...
...

publicclassMyEngineextendsorg.apache.tapestry.engine.BaseEngine{

publicstaticfinalStringAPPLICATION_CONTEXT_KEY="appContext";

/**
*@seeorg.apache.tapestry.engine.AbstractEngine#setupForRequest(org.apache.tapestry.request.RequestContext)

*/

protectedvoidsetupForRequest(RequestContextcontext){
super.setupForRequest(context);

//insertApplicationContextinglobal,ifnotthere 
Mapglobal=(Map)getGlobal();

ApplicationContextac=(ApplicationContext)global.get(APPLICATION_CONTEXT_KEY);

if(ac==null){
ac=WebApplicationContextUtils.getWebApplicationContext(
context.getServlet().getServletContext()
);
global.put(APPLICATION_CONTEXT_KEY,ac);
}
}
}

ThisengineclassplacestheSpringApplicationContextasanattributecalled"appContext"inthisTapestryapp's'Global'object.MakesuretoregisterthefactthatthisspecialIEngineinstanceshouldbeusedforthisTapestryapplication,withanentryintheTapestryapplicationdefinitionfile.Forexample:
file:xportal.application:

<?xmlversion="1.0"encoding="UTF-8"?>
<!DOCTYPEapplicationPUBLIC

"-//ApacheSoftwareFoundation//TapestrySpecification3.0//EN"

"http://jakarta.apache.org/tapestry/dtd/Tapestry_3_0.dtd">
<application

name="WhateverxPortal"

engine-class="com.whatever.web.xportal.MyEngine">
</application>
14.4.2.4.Componentdefinitionfiles

Nowinourpageorcomponentdefinitionfile(*.pageor*.jwc),wesimplyaddproperty-specificationelementstograbthebeansweneedoutoftheApplicationContext,andcreatepageorcomponentpropertiesforthem.Forexample:

<property-specificationname="userService"

type="com.whatever.services.service.user.UserService">

global.appContext.getBean("userService")
</property-specification>

<property-specificationname="authenticationService"

type="com.whatever.services.service.user.AuthenticationService">

global.appContext.getBean("authenticationService")
</property-specification>

TheOGNLexpressioninsidetheproperty-specificationspecifiestheinitialvaluefortheproperty,asabeanobtainedfromthecontext.Theentirepagedefinitionmightlooklikethis:

<?xmlversion="1.0"encoding="UTF-8"?>
<!DOCTYPEpage-specificationPUBLIC

"-//ApacheSoftwareFoundation//TapestrySpecification3.0//EN"

"http://jakarta.apache.org/tapestry/dtd/Tapestry_3_0.dtd">

<page-specificationclass="com.whatever.web.xportal.pages.Login">

<property-specificationname="username"type="java.lang.String"/>

<property-specificationname="password"type="java.lang.String"/>

<property-specificationname="error"type="java.lang.String"/>

<property-specificationname="callback"type="org.apache.tapestry.callback.ICallback"persistent="yes"/>

<property-specificationname="userService"

type="com.whatever.services.service.user.UserService">

global.appContext.getBean("userService")
</property-specification>

<property-specificationname="authenticationService"

type="com.whatever.services.service.user.AuthenticationService">

global.appContext.getBean("authenticationService")
</property-specification>

<beanname="delegate"class="com.whatever.web.xportal.PortalValidationDelegate"/>

<beanname="validator"class="org.apache.tapestry.valid.StringValidator"lifecycle="page">

<set-propertyname="required"expression="true"/>

<set-propertyname="clientScriptingEnabled"expression="true"/>
</bean>

<componentid="inputUsername"type="ValidField">

<static-bindingname="displayName"value="Username"/>

<bindingname="value"expression="username"/>

<bindingname="validator"expression="beans.validator"/>
</component>

<componentid="inputPassword"type="ValidField">

<bindingname="value"expression="password"/>

<bindingname="validator"expression="beans.validator"/>

<static-bindingname="displayName"value="Password"/>

<bindingname="hidden"expression="true"/>
</component>
</page-specification>

14.4.2.5.Addingabstractaccessors

NowintheJavaclassdefinitionforthepageorcomponentitself,allweneedtodoisaddanabstractgettermethodforthepropertieswehavedefined,toaccessthem.WhenthepageorcomponentisactuallyloadedbyTapestry,itperformsruntimecodeinstrumentationontheclassfiletoaddthepropertieswhichhavebeendefined,andhookuptheabstractgettermethodstothenewlycreatedfields.Forexample:

//ourUserServiceimplementation;willcomefrompagedefinition 

publicabstractUserServicegetUserService();

//ourAuthenticationServiceimplementation;willcomefrompagedefinition 

publicabstractAuthenticationServicegetAuthenticationService();

Forcompleteness,theentireJavaclass,foraloginpageinthisexample,mightlooklikethis:
packagecom.whatever.web.xportal.pages;

/**
*Allowstheusertologin,byprovidingusernameandpassword.
*Aftersuccessfullyloggingin,acookieisplacedontheclientbrowser
*thatprovidesthedefaultusernameforfuturelogins(thecookie
*persistsforaweek).

*/

publicabstractclassLoginextendsBasePageimplementsErrorProperty,PageRenderListener{

/**thekeyunderwhichtheauthenticateduserobjectisstoredinthevisitas*/

publicstaticfinalStringUSER_KEY="user";

/**
*Thenameofacookietostoreontheuser'smachinethatwillidentify
*themnexttimetheylogin.

**/

privatestaticfinalStringCOOKIE_NAME=Login.class.getName()+".username";

privatefinalstaticintONE_WEEK=7*24*60*60;

//---attributes 

publicabstractStringgetUsername();

publicabstractvoidsetUsername(Stringusername);

publicabstractStringgetPassword();

publicabstractvoidsetPassword(Stringpassword);

publicabstractICallbackgetCallback();

publicabstractvoidsetCallback(ICallbackvalue);

publicabstractUserServicegetUserService();

publicabstractAuthenticationServicegetAuthenticationService();

//---methods 

protectedIValidationDelegategetValidationDelegate(){

return(IValidationDelegate)getBeans().getBean("delegate");
}

protectedvoidsetErrorField(StringcomponentId,Stringmessage){
IFormComponentfield=(IFormComponent)getComponent(componentId);

IValidationDelegatedelegate=getValidationDelegate();

delegate.setFormComponent(field);

delegate.record(newValidatorException(message));
}

/**
*Attemptstologin.
*
*<p>Iftheusernameisnotknown,orthepasswordisinvalid,thenanerror
*messageisdisplayed.
*

**/

publicvoidattemptLogin(IRequestCyclecycle){
Stringpassword=getPassword();

//Doalittleextraworktoclearoutthepassword. 

setPassword(null);

IValidationDelegatedelegate=getValidationDelegate();

delegate.setFormComponent((IFormComponent)getComponent("inputPassword"));

delegate.recordFieldInputValue(null);

//Anerror,fromavalidationfield,mayalreadyhaveoccurred. 

if(delegate.getHasErrors())

return;

try{
Useruser=getAuthenticationService().login(getUsername(),getPassword());
loginUser(user,cycle);
}

catch(FailedLoginExceptionex){

this.setError("Loginfailed:"+ex.getMessage());

return;
}
}

/**
*Setsupthe{@linkUser}astheloggedinuser,creates
*acookiefortheirusername(forsubsequentlogins),
*andredirectstotheappropriatepage,or
*aspecifiedpage).
*

**/

publicvoidloginUser(Useruser,IRequestCyclecycle){
Stringusername=user.getUsername();

//Getthevisitobject;thiswilllikelyforcethe 

//creationofthevisitobjectandanHttpSession. 
Mapvisit=(Map)getVisit();
visit.put(USER_KEY,user);

//Afterloggingin,gototheMyLibrarypage,unlessotherwise 

//specified. 
ICallbackcallback=getCallback();

if(callback==null)

cycle.activate("Home");

else
callback.performCallback(cycle);

//I'vefoundthatfailingtosetamaximumageandapathmeansthat 

//thebrowser(IE5.0anyway)quietlydropsthecookie. 
IEngineengine=getEngine();

Cookiecookie=newCookie(COOKIE_NAME,username);
cookie.setPath(engine.getServletPath());
cookie.setMaxAge(ONE_WEEK);

//Recordtheuser'susernameinacookie 
cycle.getRequestContext().addCookie(cookie);
engine.forgetPage(getPageName());
}

publicvoidpageBeginRender(PageEventevent){

if(getUsername()==null)
setUsername(getRequestCycle().getRequestContext().getCookieValue(COOKIE_NAME));
}
}
14.4.3.Summary

Inthisexample,we'vemanagedtoallowservicebeansdefinedintheSpringApplicationContexttobeprovidedtothepageinadeclarativefashion.Thepageclassdoesnotknowwheretheserviceimplementationsarecomingfrom,andinfactitiseasytoslipinanotherimplementation,forexample,duringtesting.ThisinversionofcontrolisoneoftheprimegoalsandbenefitsoftheSpringFramework,andwehavemanagedtoextenditallthewayuptheJ2EEstackinthisTapestryapplication.
14.5.WebWork

WebWorkisawebframeworkdesignedwithsimplicityinmind.It'sbuiltontopofXWork,whichisagenericcommandframework.XWorkalsohasanIoCcontainer,butitisn'tasfull-featuredasSpringandwon'tbecoveredinthissection.WebWorkcontrollersarecalledActions,mainlybecausetheymustimplementtheActioninterface.TheActionSupportclassimplementsthisinterface,anditismostcommonparentclassforWebWorkactions.

WebWorkmaintainsitsownSpringintegrationproject,locatedonjava.netinthexwork-optionalproject.Currently,threeoptionsareavailableforintegratingWebWorkwithSpring:

SpringObjectFactory:overrideXWork'sdefaultObjectFactorysoXWorkwilllookforSpringbeansintherootWebApplicationContext.

ActionAutowiringInterceptor:useaninterceptortoautomaticallywireanAction'sdependenciesasthey'recreated.

SpringExternalReferenceResolver:lookupSpringbeansbasedonthenamedefinedinan<external-ref>elementofan<action>element.

AllofthesestrategiesareexplainedinfurtherdetailinWebWork'sDocumentation.
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