Hi,
If you are assking about jbpm / human task users, you can add them when you create the taskservice
TaskService taskService = new TaskService(emf, SystemEventListenerFactory.getSystemEventListener());
TaskServiceSession taskSession = taskService.createSession();
taskSession.addUser(new User("Administrator"));
taskSession.addUser(new User("....
here an example :
https://github.com/droolsjbpm/jbpm/blob/master/jbpm-examples/src/main/java/org/jbpm/examples/humantask/HumanTaskExample.java
you can load you list of users from a file or a database
HTH