Guice Scopes

This section considers Guice and in particular its relationship with Vaadin

To understand Guice itself, the Guice documentation is a good place to start. This documentation only addresses points which relate to its use in Krail

If you think you are not are not familiar with the idea of scopes, actually you probably are - at its simplest level, the principles are no different to thinking of variables having scope.

Vaadin Environment

The Vaadin architecture is significantly different to a typical Web environment. There are three scopes used by Krail to reflect Vaadin’s design:

UI Scope

UI Scope represents a Vaadin UI instance, and is generally equivalent to a browser tab. To give a class this scope, apply the @UIScoped annotation to the class and instantiate with Guice.

Vaadin Session Scope

Vaadin session scope represents a VaadinSession and is generally equivalent to a browser instance. To give a class this scope, apply the @VaadinSessionScoped annotation to the class and instantiate with Guice.

Singleton

A Singleton has only one instance in the application. To give a class this scope, apply the @Singleton annotation to the class and instantiate with Guice.

Singleton classes must be thread safe.

AOP

Guice AOP is used by Krail, and if you are not familiar with it the main points to note are:

• Guice AOP works only on method interception
• It does NOT work on private, static or final methods - this is very easy to forget when stubbing methods with an IDE!
• For Guice AOP to work, Guice must instantiate the object