@Target(value=TYPE)
 @Retention(value=RUNTIME)
public @interface IdClass

Specifies a composite primary key class that is mapped to multiple fields or properties of the entity.

The names of the fields or properties in the primary key class and the primary key fields or properties of the entity must correspond and their types must be the same.

 Example:
 @IdClass(com.acme.EmployeePK.class)
 @Entity
 public class Employee {
 @Id String empName;
 @Id Date birthDay;
 ...
 }