[JAVA] The story of @ViewScoped consuming memory

environment

Web application

Java 8
Java EE 7 (Payara 4)
JSF 2.2

phenomenon

The application died in OutOfMemory. Closed screen management beans are alive and R.I.P.

Suspicious part

Long session timeout
Some management beans eat memory

Initial flow

Common explanation

Annotation	Namespace	Lifetime
`@RequestScoped`	javax.enterprise.context.RequestScoped	One HTTP request/response
`@ViewScoped`	javax.faces.view.ViewScoped	While the views are the same
`@SessionScoped`	javax.enterprise.context.SessionScoped	Session start-end
`@ApplicationScoped`	javax.enterprise.context.ApplcationScoped	While the application is running
`@Dependent`	javax.enterprise.context.Dependent	Depends on the scope to which it was injected
`@ConversationScoped`	javax.enterprise.context.ConversationScoped	You can specify the start and end arbitrarily
`@FlowScoped`	javax.enterprise.context.FlowScoped	From start to end of a predefined flow

My understanding

Hmm. ** It is convenient if @ViewScoped is generated when the screen is opened and discarded when it is closed. ** ** You can give @SessionScoped the information of the logged-in user and create a business screen with @ViewScoped.

You can also specify the number of Views that a session holds in web.xml.

/web.xml
    <context-param>
        <param-name>javax.faces.STATE_SAVING_METHOD</param-name>
        <param-value>sever</param-value>
    </context-param>
    <context-param>
        <param-name>com.sun.faces.numberOfLogicalViews</param-name>
        <param-value>20</param-value>
    </context-param>
    <context-param>
        <param-name>com.sun.faces.numberOfViewsInSession</param-name>
        <param-value>20</param-value>
    </context-param>

Know if it will be released if the upper limit is exceeded.

When I did something like that, the management bean of @ViewScoped, which should have been destroyed, was so alive that the memory was crushed.

Actually

Apparently, the management bean of @ViewScoped will not be released unless it has the following pattern.

Postback with no results
Session expired

Therefore, it survives in the following pattern.

GET to another page
Page refresh
When the maximum number of logical views in a session is exceeded (expires but is not destroyed)

solution

Use OmniFaces @ViewScoped instead of the standard @ViewScoped. Just use the @ViewScoped annotation of ʻOmniFaces and it will release it when you pick up the ʻunload event of your browser. It is designed so as not to affect the default dependency as much as possible, so I wonder if it can be introduced just to use @ViewScoped.

Afterword

I wondered if View would be managed on a screen-by-screen basis, but it's not a screen-based unit, but a component tree-based unit, so it's wrong to expect that it will be released when the screen is closed.

It is a trap behavior that it is not discarded even if the maximum number of logical views is exceeded.

~~ Don't hold the session for a long time & don't make it huge ~~

References

jsf-2 – Why @ViewScoped Beans that have expired are not destroyed until the session expires stack overflow : JSF 2.2 Memory Consumption: Why does Mojarra keep the ViewScoped Beans of the last 25 Views in Memory?