How to retrieve user name from a given Subject?

Question

I am in a situation where I need to retrieve user name from the Subject that is populated when user logs in. I have the active Subject and I do following to get the principals in the subject and iterate through them:
Set principals = subject.getPrincipals();
Iterator ite = principals.iterator();
while (ite.hasNext()) {
Principal prin = (Principal)ite.next();
String name = prin.getName();
But this contains all the principals, including user name, roles, password, etc. How do I programmatically determine which one is user name?

Answer 1

Don't you have different principal types? I am making a jaas module and I have different principals for roles, groups etc. I think of principals as attributes, the type in the attribute name and the principal name is the attribute value.
To get all the principals of the type SomePrincipal, you can use:
Set principals = subject.getPrincipals(SomePrincipal.class)
You can also take som principal an test wether it is an instance of som type:
if (Principal p instanceof SomePrincipal){..}
An other solution which might be better if you have many different attributes is to store both attribute name and value in the name of the principal.
If "mark" is a username the principal name will be "username:mark" el.
Then it will be easy to find the username.