Five years ago,
Spring 1.0 brought Java
dependency injection into the mainstream. Three years later,
Google
Guice 1.0 introduced annotation-based dependency injection and made Java programming
a little easier. Since then, developers have had to choose between a) writing external
configuration or b) importing vendor-specific annotations.
Today, we hope
to give developers the best of both worlds.
Google Guice and SpringSource have
partnered to standardize a proven, non-controversial set of annotations that make injectable
classes portable across frameworks. At the
moment, the set of specified annotations consists of:
- @Inject - Identifies injectable
constructors, methods, and fields
- @Qualifier - Identifies qualifier
annotations
- @Scope - Identifies scope annotations
- @Named - String-based
qualifier
- @Singleton - Identifies a type that the injector only instantiates
once
One additional interface is specified for use in conjunction with
these annotations:
- Provider<T> - Provides instances of a type T. For any type T
that can be injected, you can also inject Provider<T>.
You can check out an early
draft of the
specification. We deliberately left external dependency configuration
out, so as not to quash ongoing innovation. We haven't formally submitted this standard to the
JCP yet, but we plan to do so shortly. Standards wonks can read a draft of our
JSR
proposal.
The expert group will be inclusive and will work in
the open. For example, our mailing list is publicly readable, and we host the specification at
Google
Code. Several industry players have already expressed interest in supporting this
effort.
Contact us if you'd like to help out.
Interested in learning more about dependency injection? Don't miss Jesse and
Dhanji's Big Modular Java with
Guice session at Google I/O!By Bob Lee, Google Guice founder
