java - Extract the primary key from a entity object in JPA 2.0? -

let's have entity object. there way extract primary key it?

i want this:

public static object extractprimarykey(entitymanager em, object obj) {     return em.givemetheprimarykeyofthisentityobject(obj); }

reason attached copy of detached entity:

public static object attach(entitymanager em, object obj) {     return em.find(obj.getclass(), extractprimarykey(em, obj)); }

is possible? (i using eclipselink 2.1)

perhaps work:

em.getentitymanagerfactory().getpersistenceunitutil().getidentifier(obj);

ERT