Obtain CallerPrincipal in a utility class

Question

Hi,
I'd like to obtain the caller principal of a ejb from a utility class. I know I can easily get the EJBContext inside the ejb itself using the callback from the container to the setSeccionCoontect method, but what if I need to knwo the caller principal in a utility class called by a business method of my ejb?
By the way, I'm using EJB2.1 in Weblogic 8.1 and I'm talking about SessionBeans. I know I could obtain the caller principal inside my ejb and simply pass it as a parameter to my utility class, but I dont liek to idea of adding a user parameter to my utility clases method.
I'm aware that I could do a InitialContext.lookup("java:/comp/EJBContext") if I was using a EJB3 container, but I cant find the equivalent with EJB2.
Thanks!

Answer 1

Every thread has a stack of its own and its own copies of local variables, if a static method uses only locals it doesn't have to be synchronized.
Using lazy initialization with the singleton pattern is a good example of side effects. Examine this code:class Singleton {
    static Singleton instance;
    static Singleton getInstance() {
        if (instance == null) instance = new Singleton();
        return instance;
    // don't allow other classes to create an instance
    private Singleton() {}
}Now what happens if two threads simultaneously enter the getInstance method and both find the value of the "instance" variable null in the if-condition? You end up creating an instance of the class twice, which is not what you want. This can be solved by writing the method declaration as "synchronized static Singleton getInstance()" so no two threads can enter the method simultaneously.