class BookService {
    static scope = "session"
    ...
}
scope
Purpose
Changes the scope of a service
Examples
Description
By default services are "singleton" scoped which means that clients of a service only ever use a single instance (a singleton) of the service. This behaviour can be changed by specifying a scope attribute with on the following values:
- 
prototype- A new service is created every time it is injected into another class - 
request- A new service will be created per request - 
flash- A new service will be created for the current and next request only - 
flow- In web flows the service will exist for the scope of the flow - 
conversation- In web flows the service will exist for the scope of the conversation. ie a root flow and its sub flows - 
session- A service is created for the scope of a user session - 
singleton(default) - Only one instance of the service ever exists 
See Scoped Services in the user guide for more information.