How to choose the right bean scope

Question

I noticed that there are different bean scopes like    RequestScoped  ViewScoped  FlowScoped  SessionScoped  ApplicationScoped   What is the purpose of each  How do I choose a proper scope for my bean

User · Answer

Since JSF 2 3 all the bean scopes defined in package javax faces bean package have been deprecated to align the scopes with CDI  Moreover they re only applicable if your bean is using  ManagedBean annotation  If you are using JSF versions below 2 3 refer to the legacy answer at the end     From JSF 2 3 here are scopes that can be used on JSF Backing Beans   1   javax enterprise context ApplicationScoped  The application scope persists for the entire duration of the web application  That scope is shared among all requests and all sessions  This is useful when you have data for whole application   2   javax enterprise context SessionScoped  The session scope persists from the time that a session is established until session termination  The session context is shared between all requests that occur in the same HTTP session  This is useful when you wont to save data for a specific client for a particular session   3   javax enterprise context ConversationScoped  The conversation scope persists as log as the bean lives  The scope provides 2 methods  Conversation begin   and Conversation end    These methods should called explicitly  either to start or end the life of a bean   4   javax enterprise context RequestScoped  The request scope is short-lived  It starts when an HTTP request is submitted and ends after the response is sent back to the client  If you place a managed bean into request scope  a new instance is created with each request  It is worth considering request scope if you are concerned about the cost of session scope storage   5   javax faces flow FlowScoped  The Flow scope persists as long as the Flow lives  A flow may be defined as a contained set of pages  or views  that define a unit of work  Flow scoped been is active as long as user navigates with in the Flow    6   javax faces view ViewScoped  A bean in view scope persists while the same JSF page is redisplayed  As soon as the user navigates to a different page  the bean goes out of scope     The following legacy answer applies JSF version before 2 3     As of JSF 2 x there are 4 Bean Scopes               SessionScoped     RequestScoped    ApplicationScoped    ViewScoped            Session Scope     The session scope persists from the time that a session is established until session termination  A session terminates   if the web application invokes the invalidate method on the   HttpSession object  or if it times out       RequestScope    The request scope is short-lived  It starts when an HTTP request is submitted and ends after the response is sent back   to the client  If you place a managed bean into request scope  a new   instance is created with each request  It is worth considering request   scope if you are concerned about the cost of session scope storage       ApplicationScope     The application scope persists for the entire duration of the web application  That scope is shared among all   requests and all sessions  You place managed beans into the   application scope if a single bean should be shared among all   instances of a web application  The bean is constructed when it is   first requested by any user of the application  and it stays alive   until the web application is removed from the application server       ViewScope       View scope was added in JSF 2 0  A bean in view scope persists while the same JSF page is redisplayed   The JSF   specification uses the term view for a JSF page   As soon as the user   navigates to a different page  the bean goes out of scope       Choose the scope you based on your requirement    Source  Core Java Server Faces 3rd Edition by David Geary  amp  Cay Horstmann  Page no  51 - 54

User · Answer

Introduction It represents the scope  the lifetime  of the bean  This is easier to understand if you are familiar with  quot under the covers quot  working of a basic servlet web application  How do servlets work  Instantiation  sessions  shared variables and multithreading    Request View Flow Session ApplicationScoped A  RequestScoped bean lives as long as a single HTTP request-response cycle  note that an Ajax request counts as a single HTTP request too   A  ViewScoped bean lives as long as you re interacting with the same JSF view by postbacks which call action methods returning null void without any navigation redirect  A  FlowScoped bean lives as long as you re navigating through the specified collection of views registered in the flow configuration file  A  SessionScoped bean lives as long as the established HTTP session  An  ApplicationScoped bean lives as long as the web application runs  Note that the CDI  Model is basically a stereotype for  Named  RequestScoped  so same rules apply  Which scope to choose depends solely on the data  the state  the bean holds and represents  Use  RequestScoped for simple and non-ajax forms presentations  Use  ViewScoped for rich ajax-enabled dynamic views  ajaxbased validation  rendering  dialogs  etc   Use  FlowScoped for the  quot wizard quot    quot questionnaire quot   pattern of collecting input data spread over multiple pages  Use  SessionScoped for client specific data  such as the logged-in user and user preferences  language  etc   Use  ApplicationScoped for application wide data constants  such as dropdown lists which are the same for everyone  or managed beans without any instance variables and having only methods  Abusing an  ApplicationScoped bean for session view request scoped data would make it to be shared among all users  so anyone else can see each other s data which is just plain wrong  Abusing a  SessionScoped bean for view request scoped data would make it to be shared among all tabs windows in a single browser session  so the enduser may experience inconsitenties when interacting with every view after switching between tabs which is bad for user experience  Abusing a  RequestScoped bean for view scoped data would make view scoped data to be reinitialized to default on every single  ajax  postback  causing possibly non-working forms  see also points 4 and 5 here   Abusing a  ViewScoped bean for request  session or application scoped data  and abusing a  SessionScoped bean for application scoped data doesn t affect the client  but it unnecessarily occupies server memory and is plain inefficient  Note that the scope should rather not be chosen based on performance implications  unless you really have a low memory footprint and want to go completely stateless  you d need to use exclusively  RequestScoped beans and fiddle with request parameters to maintain the client s state  Also note that when you have a single JSF page with differently scoped data  then it s perfectly valid to put them in separate backing beans in a scope matching the data s scope  The beans can just access each other via  ManagedProperty in case of JSF managed beans or  Inject in case of CDI managed beans  See also   Difference between View and Request scope in managed beans Advantages of using JSF Faces Flow instead of the normal navigation system Communication in JSF2 - Managed bean scopes    CustomScoped NoneScoped Dependent It s not mentioned in your question  but  legacy  JSF also supports  CustomScoped and  NoneScoped  which are rarely used in real world  The  CustomScoped must refer a custom Map lt K  Bean gt  implementation in some broader scope which has overridden Map put   and or Map get   in order to have more fine grained control over bean creation and or destroy  The JSF  NoneScoped and CDI  Dependent basically lives as long as a single EL-evaluation on the bean  Imagine a login form with two input fields referring a bean property and a command button referring a bean action  thus with in total three EL expressions  then effectively three instances will be created  One with the username set  one with the password set and one on which the action is invoked  You normally want to use this scope only on beans which should live as long as the bean where it s being injected  So if a  NoneScoped or  Dependent is injected in a  SessionScoped  then it will live as long as the  SessionScoped bean  See also   Expire specific managed bean instance after time interval what is none scope bean and when to use it  What is the default Managed Bean Scope in a JSF 2 application    Flash scope As last  JSF also supports the flash scope  It is backed by a short living cookie which is associated with a data entry in the session scope  Before the redirect  a cookie will be set on the HTTP response with a value which is uniquely associated with the data entry in the session scope  After the redirect  the presence of the flash scope cookie will be checked and the data entry associated with the cookie will be removed from the session scope and be put in the request scope of the redirected request  Finally the cookie will be removed from the HTTP response  This way the redirected request has access to request scoped data which was been prepared in the initial request  This is actually not available as a managed bean scope  i e  there s no such thing as  FlashScoped  The flash scope is only available as a map via ExternalContext getFlash   in managed beans and   flash  in EL  See also   How to show faces message in the redirected page Pass an object between  ViewScoped beans without using GET params CDI missing  ViewScoped and  FlashScoped

[jsf] How to choose the right bean scope?

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