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The Web Beans (JSR-299) specification defines a set of services for the Java EE environment that makes applications much easier to develop. Web Beans layers an enhanced lifecycle and interaction model over existing Java component types including JavaBeans and Enterprise Java Beans. As a complement to the traditional Java EE programming model, the Web Beans services provide:
an improved lifecycle for stateful components, bound to well-defined contexts,
a typesafe approach to dependency injection,
interaction via an event notification facility, and
a better approach to binding interceptors to components, along with a new kind of interceptor, called a decorator, that is more appropriate for use in solving business problems.
Dependency injection, together with contextual lifecycle management, saves the user of an unfamiliar API from having to ask and answer the following questions:
what is the lifecycle of this object?
how many simultaneous clients can it have?
is it multithreaded?
where can I get one from?
do I need to explicitly destroy it?
where should I keep my reference to it when I'm not using it directly?
how can I add an indirection layer, so that the implementation of this object can vary at deployment time?
how should I go about sharing this object between other objects?
A Web Bean specifies only the type and semantics of other Web Beans it depends upon. It need not be aware of the actual lifecycle, concrete implementation, threading model or other clients of any Web Bean it depends upon. Even better, the concrete implementation, lifecycle and threading model of a Web Bean it depends upon may vary according to the deployment scenario, without affecting any client.
Events, interceptors and decorators enhance the loose-coupling that is inherent in this model:
event notifications decouple event producers from event consumers,
interceptors decouple technical concerns from business logic, and
decorators allow business concerns to be compartmentalized.
Most importantly, Web Beans provides all these facilities in a typesafe way. Web Beans never uses string-based identifiers to determine how collaborating objects fit together. And XML, though it remains an option, is rarely used. Instead, Web Beans uses the typing information that is already available in the Java object model, together with a new pattern, called binding annotations, to wire together Web Beans, their dependencies, their interceptors and decorators and their event consumers.
The Web Beans services are general and apply to the following types of components that exist in the Java EE environment:
all JavaBeans,
all EJBs, and
all Servlets.
Web Beans even provides the necessary integration points so that other kinds of components defined by future Java EE specifications or by non-standard frameworks may be cleanly integrated with Web Beans, take advantage of the Web Beans services, and interact with any other kind of Web Bean.
Web Beans was influenced by a number of existing Java frameworks, including Seam, Guice and Spring. However, Web Beans has its own very distinct character: more typesafe than Seam, more stateful and less XML-centric than Spring, more web and enterprise-application capable than Guice.
Most importantly, Web Beans is a JCP standard that integrates cleanly with Java EE, and with any Java SE environment where embeddable EJB Lite is available.
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