A comparative look at three popular dependency injection frameworks: Spring, Guice, and OSGi declarative services. Supporting code is found at https://github.com/rombert/email-sender .

1. Dependency Injection – Spring, Guice, OSGi
Dependency Injection – Spring, Guice, OSGi
Robert Munteanu, Adobe Systems Inc
http://robert.muntea.nu
@rombert

2. $ whoami
$DAYJOB
•
Computer Scientist at
Adobe Systems Inc
FOSS
•
Apache Sling
•
MantisBT
•
•
http://robert.muntea.nu
Mylyn Connector for
MantisBT
Mylyn Connector for
Review Board
@rombert

3. Why Dependency Injection?
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Drive out accidental complexity
•
•
Leave the boilerplate to others
Decouple collaborators
•
Increase reusability
•
Ease testing
•
Increase coherence
http://robert.muntea.nu
@rombert

4. Accidental complexity – locating a service
ctx = new InitialContext();
ds =
(DataSource)ctx.lookup("jdbc/fastCoffeeDB");
http://robert.muntea.nu
@rombert

5. Accidental complexity – manually wiring components
DataSource ds = getDataSource(); // OK impl ;-)
AddressDao dao = new AddressDao(ds);
PersistenceComponent pc = new
PersistenceComponent(dao);
ServerConfig cfg = new ServerConfig(props);
ServerComponent sc = new ServerComponent(cfg);
Application app = new
Application(Arrays.asList(pc, sc));
app.start();
http://robert.muntea.nu
@rombert

6. Decouple collaborators – ease testing
public class ServiceMonitor {
public notifyIfDown() {
Service s =
ServiceFactory.getServiceToCheck();
try
{
s.connect()
} catch ( ServiceException e) {
ServiceFactory.getNotificationService().notifyOf
(e);
}
}
}
http://robert.muntea.nu
@rombert

7. Decouple collaborators – increase reusability
Service 2
Service 1
Service
AppContext 1
http://robert.muntea.nu
@rombert

8. Decouple collaborators – increase coherence
TextFormatter
EmailSender
SmtpService
RecipientFinder
http://robert.muntea.nu
@rombert

9. Dependency Injection – walkthrough
Image courtesy of FreeFoto.com
http://robert.muntea.nu
@rombert

10. Dependency Injection – walkthrough
Email Sender App
Technologies
Deliver formatted email
to large number of
recipients
Spring 3.2 - JavaConfig
http://robert.muntea.nu
Guice 3.0
OSGi DS 1.6.2
@rombert

11. Dependency Injection – bottom line
All frameworks prevent accidental complexity
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Different binding approaches
•
•
Spring binds beans
•
Guice and OSGi bind services to consumers
Different approaches to run-time composition
•
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Spring and Guice have a static view of the world
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OSGi is dynamic by definition
•
Which view is right for you?
http://robert.muntea.nu
@rombert

12. Dependency Injection – bottom line
Different approaches to scopes
•
•
Spring and OSGi default to singleton
•
Guice defaults to instance
Different approaches to instantation
•
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Spring and Guice default to eager
•
OSGi (SCR) defaults to lazy
http://robert.muntea.nu
@rombert

13. Dependency Injection – resources
https://github.com/rombert/email-sender
Dependency Injection – Dhanji R. Prasanna
Java Application Arhitecture – Kirk Knoernschild
http://robert.muntea.nu
@rombert

14. Dependency Injection – getting a hold of services
Q&A
http://robert.muntea.nu
@rombert