Will a singleton created in struts action persist?

Question

If I instantiate a Singleton class in a Struts action, will it be persistent for other request firing up that action ?

I mean, if I'm in a Struts action code and I write:

Singleton object = Singleton.getInstance();

will the object exist when another user fires up the same or another action requiring that object ?

Answer 1

I get your doubt:

since Struts2 Actions are ThreadLocal, and hence every action, on every request, creates an instance of its object, will a Singleton behave correctly ?

From your code it seems you are referring to the pre-1.5* Singleton:

public class Singleton {
    private static final Singleton INSTANCE = new Singleton();

    private Singleton() {}

    public static Singleton getInstance() {
        return INSTANCE;
    }
}

The answer is yes:

private static final Singleton INSTANCE = new Singleton();

since static "wins" over ThreadLocal, and makes it unique (instantiated once, then shared).

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*Note that if you are on Java EE >= 6, there are many ways to handle Singletons better than this, with CDI, EJB3, etc... eg @Singleton EJB or @Singleton injections.