Grails(6)Guide Book Chapter 7 The Web Layer

Grails(6)GuideBookChapter7TheWebLayer

7TheWebLayer

7.1Controllers

Acontrollercangeneratetheresponsedirectlyordelegatetoaview.

Tocreateacontroller,simplycreateaclasswhosenameendswithControllerinthegrails-app/controllersdirectory.

ThedefaultURLMappingconfigurationensuresthatthefirstpartofyourcontrollernameismappedtoaURIandeachactiondefinedwithinyourcontrollermapstotheURIswithinthecontrollernameURI.

7.1.1UnderstandingControllersandActions

Creatingacontroller

Thereare2commandscreate-controllerandgenerate-controller

>grailscreate-controllerbook

Tocreateafile/grails-app/controllers/myapp/BookController.groovy

CreatingActions

Acontrollercanhavemultiplepublicactionmethods,eachonemapstoaURI

classBookController{

deflist(){

//docontrollerlogic,getamodel

returnmodel

}

}

ThismethodwillmaptotheURI/book/list

PublicMethodsasActions

TheDefaultAction

ThedefaultactionoftheController,forexample,if/bookishit,theactionthatiscalledwhenthedefaultURIisrequestedisdictatedbythefollowingrules.

1.Ifthereisonlyoneaction,itisthedefault

2.Ifyouhaveanactionnamedindex,itisthedefault

3.AlternativelyyoucansetitexplicitlywiththedefaultActionproperty.

staticdefaultAction="list"

7.1.2ControllersandScopes

AvailableScopes

Scopesarehash-likeobjectswhereyoucanstorevariables.

servletContext-applicationscope,instanceofSevletContent

session-aninstanceofHttpSession

request-aninstanceofHttpServletRequest

params-mutablemapofincomingrequestquerystringorPOSTparameters

flash-

AccessingScopes

classBookController{

deffind(){

deffindBy=params["findBy"]

defappContext=request["foo"]

defloggedUser=session["logged_user"]

}

}

Orwecanvisittheparameterslikethis

deffind(){

deffindBy=params.findBy

defappContext=request.foo

defloggedUser=session.logged_user

}

UsingFlashScope

Flashscopeasatemporarystoretomakeattributesavailableforthisrequestandthenextrequestonly.Afterwardstheattributesarecleared.

Thisisreallyusefulforsettingamessagedirectlybeforeredirecting.

defdelete(){

defb=Book.get(params.id)

if(!b){

flash.message="Usernotfoundforid${params.id}"

redirect(action:list)

}

…snip...

}

ScopedControllers

Thereareseveralscopessupportedbygrails:

prototype(default)-Anewcontrollerwillbecreatedforeachrequest.

session-Onecontrolleriscreatedforthescopeofausersession

singleton-Onlyoneinstanceofthecontrollereverexists

Toconfigurethatincontroller

staticscope="singleton"

ToconfigurethatforallthecontrollersinConfig.groovy

grails.controllers.defaultScope="singleton"

7.1.3ModelsandViews

ReturningtheModel

AmodelisaMapthattheviewuseswhenrendering.

defshow(){

[book:Book.get(params.id)]

}

classBookController{

Listbooks

Listauthors

deflist(){

books=Book.list()

authors=Author.list()

}

}

Thesearefordefaultsettings,wecanuseModelAndViewdirectly.

defindex(){

deffavoriteBooks=…

returnnewModelAndView("/book/list",[bookList:favoriteBooks])

}

Onethingtobearinmindisthatcertainvariablenamescannotbeused

attributes,application

SelectingtheView

FortheshowAction,

classBookController{

defshow(){

[book:Book.get(params.id)]

}

}

Grailswilllookforaviewatthelocationgrails-app/views/book/show.gsp

Ifwewanttocontrolthat,weneedtorendertoadifferentview,weuserendermethod:

defshow(){

defmap=[book:Book.get(params.id)]

render(view:"display",model:map)//grails-app/views/book/display.gsp

}

defshow(){

defmap=[book:Book.get(params.id)]

render(view:"/shared/display",model:map)//grails-app/views/shared/display.gsp

}

RenderingaResponse

Rendersnippetsoftextorcodestotheresponsedirectlyfromthecontroller.

render"HelloSillycat!"

render(text:"<xml>SomeXml</xml>",contentType:"text/xml",encoding:"UTF-8")

References:

http://grails.org/doc/latest/guide/index.html

http://grails.org/doc/latest/guide/theWebLayer.html