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When to use Dependency Injection

Tuesday, January 20, 2009
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Labels: Misko Hevery

13 comments :

  1. Tim O'BrienJanuary 20, 2009 at 10:08:00 PM PST

    Don't forget Plexus. I think more people are unwittingly using Plexus every day than something like Pico, it is at the core of Maven.

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  2. Hamlet D'ArcyJanuary 21, 2009 at 7:50:00 AM PST

    I'll defend Spring here...

    Spring has a very good deployment package and you can easily only include the DI jars and not include all the others. Don't use what you don't need.

    Spring supports annotations, in fact I would have said it is the recommended configuration choice. There is no data to support the claim though.

    Spring supports constructor injection, and again I would have said it is the recommended approach. No data though.

    Spring also has great support for autowiring JUnit tests. Cool! Check it out: http://is.gd/gIcB

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  3. David LinsinJanuary 22, 2009 at 3:32:00 AM PST

    I agree with Hamelt here. I'm using Spring every day and I only use it with constructor injection.

    However, if you are referring to the Spring Documentation, you are indeed right.

    The Spring team generally advocates the usage of setter injection, since a large number of constructor arguments can get unwieldy, especially when some properties are optional.

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  4. Blair ZajacJanuary 23, 2009 at 11:23:00 AM PST

    Spring has a JavaConfig that is in beta which allows one to use DI in Java (or Scala code for that matter) without using any XML.

    I understand it is possible to mix JavaConfig with XML, but I haven't done that on any of my projects.

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  5. Gavin BongJanuary 26, 2009 at 8:21:00 PM PST

    One of the problems I face with Guice is the fact that a Provider only provides a #get() method. Is there a feature to pass in parameters to a variant of the get method like AssistedInject ? Does Spring have a comparable thing to Providers ?

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  6. Dhanji R. PrasannaJanuary 27, 2009 at 8:29:00 PM PST

    @andorra Yes Spring has "Factory" interfaces, which are the same thing, but they are not available by default and are not type safe last I checked.

    Spring also has an assisted inject equivalent with Factory methods (and interfaces), which uses method decoration. Again, it is a bit clunky but it's there.

    @Hamlet
    Annotations != type safety
    JavaConfig is also not type safe, like Guice's binder API.

    As for other features, Guice has much more compelling servlet and JPA stories, which are 90% of use cases in the kitchen sink.

    Disclaimer: I am a Guice team member.

    Dhanji.

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  7. Blair ZajacJanuary 27, 2009 at 9:46:00 PM PST

    @Dhanji

    Can you explain more the statement "JavaConfig is not ype safe". With JavaConfig, everything is done in Java code so it checks all the types.

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  8. Dhanji R. PrasannaJanuary 27, 2009 at 10:07:00 PM PST

    @Blair

    Oops, I meant to say JavaConfig *AOP* is also not typesafe.

    Dhanji. =)

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  9. DEPRECATEDpeterssonJanuary 27, 2009 at 11:36:00 PM PST

    i am using spring in my dayjob and guice in my pet projects, both for about half a year.

    both have increased my productivity drastically.

    spring seems to have an advantage at the business side - as a manager, you will recruit a spring expert easier than a guice expert.

    on the other hand, it seems much easier to mess up the spring configuration, than the guice config. @Inject apeared more intuitive to my coworkers on the pet project than using the external config.

    what bothers me in both cases: there seems to be a tendency to view the injector/webappcontext as a super-factory.

    so i've seen the approach that should be used as a last resort more often than i should:

    StaticUtils.injectorFromservletContext(). getInstance( SomeDao.class );
    SpringUtils.getBean("someDao");

    in 99% of the cases, this is wrong, since you could simply inject the right class using @Inject or as a < property >. effectively you transform your class to a top-level class by abusing the DI container this way.

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  10. Chad WoolleyFebruary 10, 2009 at 11:22:00 PM PST

    Use Ruby and you won't need a DI framework:

    * http://rubyconf.org/talks/18
    * http://rubyconf2008.confreaks.com/recovering-from-enterprise.html

    ...although I disagree with Jamis that DI is completely unnecessary (you can hear me on the video) - DI is still a valuable architecture, even in Ruby. Like testing, it generally leads programmers to do Good Things - such as loose coupling and high cohesion.

    Unfortunately, most Ruby frameworks (such as Rails) are architected in a way that pretty much precludes the widespread or high-level use of DI in your app.

    However, if you are not constrained by a framework, DI is an excellent way to structure your app. Start with a simple Registry pattern which builds your App and take it from there (like this: http://geminstaller.rubyforge.org/code/coverage/lib-geminstaller-registry_rb.html). Simple, maybe ugly, but the result of pure YAGNI TDD and completely functional (btw, this started out with Needle but I scrapped it because it was my only external dependency).

    -- Chad

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  11. iSilver LabsOctober 12, 2010 at 11:06:00 AM PDT

    We just developed a open source Light Weight Ioc / Dependency Injection framework. Can you have a look?

    http://blog.isilverlabs.com/2010/08/lightweight-ioc-dependency-injection-framework/

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  12. Nikita NaikAugust 31, 2011 at 9:28:00 PM PDT

    i am planning make my project on inversion of control/dependency injection.can anybody please suggest me from where actually my project should start????? reply as soon as possible...i need your help because i have understood the concept but unable to implement.

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  13. Nikita NaikAugust 31, 2011 at 9:32:00 PM PDT

    please let me know how to make framework using dependency injection??? and how to implement the concept of inversion control

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