@UniqueConstraint and @Column Unique attribute.

@Entity
@Table(uniqueConstraints=
           @UniqueConstraint(columnNames = {"email", "empl_id"})) 
public class EntityClass {
    ...
}

@Entity
@Table(name="USER_TABLE") 
public class User{
  @Id
  @Column(name = "ID")
  private String id;

  @Column(name = "SSN", unique=true)
  private String ssnumber;