JSF backing bean should be serializable?

I'm getting these messages:

[#|2010-07-30T11:28:32.723+0000|WARNING|glassfish3.0.1|javax.faces|_ThreadID=37;_ThreadName=Thread-1;|Setting non-serializable attribute value into ViewMap: (key: MyBackingBean, value class: foo.bar.org.jsf.MyBackingBean)|#]

Do these mean that my JSF backing beans should implement Serializable? Or are they refering to some other problem?

Solution 1:

Yes, you understood it correctly. The view is basically stored in the session scope. The session scope is in JSF backed by the Servlet's HttpSession. All session attributes are supposed to implement Serializable, this because the average servletcontainer may persist session data to harddisk among others to be able to share with other servers in a cluster, or to survive heavy load, or to revive sessions during server restart.

Storing raw Java objects on harddisk is only possible if the respective class implements Serializable. Then ObjectOutputStream can be used to write them to harddisk and ObjectInputStream to read them from harddisk. The servletcontainer manages this all transparently, you actually don't need to worry about it. JSF is just giving a warning so that you understand the risks.