dependency injection

Dependency Injection Options for Java

by on February 17, 2014 8:49 am

I wanted to take some time to put together a summary of some popular dependency injection (DI) frameworks for Java. This is a high-level overview of what’s available.

First off, what is dependency injection?

“Dependency injection is a software design pattern that allows the removal of hard-coded dependencies and makes it possible to change them, whether at run-time or compile-time.” – Wikipedia

If you’ve ever had a constructor with 12 parameters, you’ve already encountered a compelling reason to use dependency injection.

Most objects require references to other objects to be useful. Dependency injection allows the system to provide those references without you having to manage all of those dependencies at the application level.

This sounds complicated, but it’s really not. Since this is not an in-depth discussion of dependency injection, check out the Wikipedia page for several examples in various languages.

Dagger

Beginning with one of the simplest, most lightweight frameworks available, Dagger is a tiny library (<100KB) that is useful for programs that must minimize their footprint, as in the case of mobile applications. It lacks many of the features of the larger frameworks, but it makes it up in speed and a neat compile-time validation tool.

Google Guice

Guice is Google’s attempt to create a feature-rich, independent DI facility. It is useful in most applications, especially web development. It provides a lot more features than Dagger, but it is slower and can be complex.

Spring DI

Spring is huge. It’ll do everything for you, even write perl so that the perl can then do your laundry. Of course it has dependency injection.

The upside is that if you are already using Spring, enabling and using DI is very easy and makes for a very well integrated approach.

The downside is that if Spring isn’t your thing or you are trying to add DI to an existing enterprise application, it may be challenging to isolate the small subset of features that you want to use.

Spring DI can be configured either through XML or through annotations. I strongly recommend the annotated approach. It is much easier to traverse in code and can provide significant insights to developers that need to understand what’s going on.

Java EE6 CDI

CDI is the Context and Dependency Injection framework that is included in Java Enterprise Edition. On the surface, it looks very similar to Spring’s annotation-based DI mechanism and, in reality, it is. There are some things that it does differently under the covers, but for the most part it is attempting to solve exactly the same problems for the Java EE crowd.

PicoContainer

I mention this one last because I just came across it while poking around the internet. PicoContainer, like Dagger, is a very small framework that intends to do a few things very well. It doesn’t have the features or complexity of Spring or CDI, and in exchange you get simplicity.

I don’t know much about this one but I am now aware of its existence. A new adventure every day!

Deduplication

This post was published with the permission of one of our software consultants, Shannon Griswold (www.thegrisexplores.com). Original text can be found here.

— Shannon Griswold, asktheteam@keyholesoftware.com

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8 responses to “Dependency Injection Options for Java”

  1. […] Google Guice is a lightweight injection framework that alleviates the need for the common Factory Patterns many developers turn to when needing to marshal the creation of objects. RoboGuice is an extension of that framework built specifically for Android to help developers cover typical tasks in Android development. There are also other frameworks available, so check out the post by Keyhole’s Shannon Griswold on some of the alternatives – Dependency Injection Options for Java. […]

  2. As a note, Dagger is a Google/Square joint thing. Dagger2 is nearly early access, and is more feature-filled than Dagger 1, 100% compile-time, faster, and has a cleaner configuration model. It lives at http://github.com/google/dagger – the Square folks have given us the go-ahead for the google fork to be canonical for Dagger 2.

  3. Robert says:

    I find Dagger to go in the right direction to eliminate implicit/hidden stuff, but I find it does not go the extra “really no magic” mile. I think that code generation (annotation processing) qualifies as magic in this regard.

    If you allow a shameless plug, check out https://github.com/vanillasource/jaywire, which is pure Java 8 Code, less than 20K. If you want explicit dependency wiring, maybe that is what you are looking for.

  4. LG says:

    I created my own injector in a couple of hours. It can inject in static fields, create instances on the fly, it scans the whole classpath for @Component and @Inject, it differentiates singletons and multitons, it can even scan for concrete implementation of abstract components and inject them It also inject loggers with right class type, and much more. It is composed of 4 classes, a bunch of Java 8 , is simple and super fast. I just DONT GET why people use Spring and other shit. People are getting lazier and lazier. everything must use ” industry standard framework BLABLA” .. write your own stuff ! nothing can be more industry standard than that…

    • Zoli says:

      Usually people also use other features of Spring.
      The other reason is time to market. People already knows Spring and they don’t need to write their own DI and test it. If they need some extra functionality like lifecycle management they don’t need to extend their “framework” and spend time on it. Somebody wants to work on your code? Cool, let’s learn your custom DI for it…
      Everybody want to create their own framework…

      • Robert says:

        The other side of that coin is when Time to Market dominates architecture decisions and only short term values are recognized.

        Estimating the real cost of making something vs. getting something off-the-shelf is really hard. It is however easy when you only plan short term, which is exactly the reason it is usually only planned short term. But that is a whole other (off-topic) discussion…

        In general I agree with LG, that the decision to use something as complicated as Spring, CDI, EJBs or JSF is often not made based on technical merits or even Time to Market, is just a lazy default position.

        Injection IS easy, and it shouldn’t require a complex library or runtime. And if a few days of coding can cover the requirements of a particular project, that sounds pretty good to me versus getting a big bundle of third party dependencies.

  5. Adam says:

    Here is another minimalist DI implementation: https://github.com/AdamSkywalker/ray

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