This document discusses dependency injection frameworks Guice and Dagger. It provides an overview of how Netflix uses Guice for projects like Governator and Karyon. It also explains how Dagger works by generating code at compile time to create a dependency injection graph, allowing for faster initialization than reflection-based frameworks. Examples are given of how to declare dependencies and satisfy them in both Guice and Dagger.

1. Using and contributing to the
next Guice
Adrian Cole
@adrianfcole #netflixoss
http://www.linkedin.com/in/adrianforrestcole

2. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

3. Adrian
• cloud guy at Netflix
• founded jclouds
• focus on (small) libraries

4. thanks
@jessewilson
• Guice
• javax.inject
• Android Core Libraries
• Dagger

5. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

6. Wiring With
Guice!

7. (cc) creative commons from flickr.com/photos/uscpsc/7894303566/

8. class Thermosiphon implements Pump {
private final Heater heater;
Thermosiphon(Heater heater) {
this.heater = heater;
}
@Override public void pump() {
if (heater.isHot()) {
System.out.println("=> => pumping => =>");
}
}
}

9. class Thermosiphon implements Pump {
private final Heater heater;
@Inject
Thermosiphon(Heater heater) {
this.heater = heater;
}
...
}
Declare
Dependencies

10. class CoffeeMaker {
@Inject Heater heater;
@Inject Pump pump;
...
}
Declare
Dependencies

11. class DripCoffeeModule extends AbstractModule {
@Overrides void configure() {
bind(Heater.class).to(ElectricHeater.class);
bind(Pump.class).to(Thermosiphon.class);
}
}
Satisfy Dependencies

12. class CoffeeApp {
public static void main(String[] args) {
Injector injector
= Guice.createInjector(
new DripCoffeeModule());
CoffeeMaker coffeeMaker
= injector.getInstance(CoffeeMaker.class);
coffeeMaker.brew();
}
}
Build the Injector

13. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

14. Netflix uses lots of
Guice
• Governator
– Governate (verb) to wire together an app so that
it implicitly bootstraps and exposes its lifecycle.
• Karyon
– Karyonate (verb) unpronouncable… so
– Blueprint for a web app or REST service

15. Governator Bootstrap
• Extends Guice
– classpath scanning and automatic binding
– lifecycle management
– configuration to field mapping
– field validation
– parallelized object warmup
• Some overlap with Apache Onami

16. class DieselHeater implements Heater {
...
@PostConstruct void startEngine() {
// mmm… exhaust with coffee..
}
}
Define
@PostConstruct

17. class CoffeeApp {
public static void main(String[] args) {
Injector injector
= LifeCycleInjector.createInjector(
new DripCoffeeModule());
CoffeeMaker coffeeMaker
= injector.getInstance(CoffeeMaker.class);
coffeeMaker.brew();
}
}
Build the Injector

18. Karyon
• Web Service Blueprint
– Extends Governator, Guice Servlet
– Built-in Admin Console
– Pluggable Web Resources
– Cloud-Ready hooks
@Application has @Components
Usually has a HealthCheckHandler

19. @Component(disableProperty = “killswitch”)
class DieselHeater implements Heater {
...
@PostConstruct void startEngine() {
// mmm… exhaust with coffee..
}
}
Define @Component

20. appName.properties
com.netflix.karyon.server.base.packages=
com.foo.appName.components
Check config

21. A Cloud Native Open Source Platform
@adrianfcole #netflixoss
More?

22. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

23. Dagger
Slides by Jesse Wilson from Square
A fast dependency injector for
Android and Java.

24. •Dagger
–Motivation
–Using Dagger
–Inside Dagger

25. Motivation for Dependency
Injection
• Decouple concrete from concrete
• Uniformity

26. Dependency Injection
Choices
• PicoContainer
• Spring
• Guice
• javax.inject

27. (cc) creative commons from flickr.com/photos/getbutterfly/6317955134/

28. (cc) creative commons from flickr.com/photos/wikidave/2988710537/

29. We still love you, Froyo
• Eager vs. lazy graph construction
• Reflection vs. codegen

30. typicalprogrammer.com/?p=143
“I didn’t really expect anyone to use
[git] because it’s so hard to use, but
that turns out to be its big appeal.
No technology can ever be too
arcane or complicated for the black t-
shirt crowd.”
–Linus Torvalds

31. No black t-shirt necessary

32. (cc) creative commons from flickr.com/photos/mike_miley/5969110684/

33. • Know everything at
build time.
• Easy to see how
dependencies are
used & satisfied

34. Motivation for Dagger
• It's like Guice, but with speed instead
of features
• Simple
• Predictable
also...

35. •Dagger
–Motivation
–Using Dagger
–Inside Dagger

36. Directed
Acyclic
Graph
DAGger.

37. (cc) creative commons from flickr.com/photos/uscpsc/7894303566/

38. class Thermosiphon implements Pump {
private final Heater heater;
Thermosiphon(Heater heater) {
this.heater = heater;
}
@Override public void pump() {
if (heater.isHot()) {
System.out.println("=> => pumping => =>");
}
}
}

39. class Thermosiphon implements Pump {
private final Heater heater;
@Inject
Thermosiphon(Heater heater) {
this.heater = heater;
}
...
}
Declare
Dependencies

40. class CoffeeMaker {
@Inject Heater heater;
@Inject Pump pump;
...
}
Declare
Dependencies

41. @Module(injects = CoffeeMakerApp.java)
class DripCoffeeModule {
@Provides Heater provideHeater() {
return new ElectricHeater();
}
@Provides Pump providePump(Thermosiphon pump) {
return pump;
}
}
Satisfy Dependencies

42. class CoffeeApp {
public static void main(String[] args) {
ObjectGraph objectGraph
= ObjectGraph.create(new DripCoffeeModule());
CoffeeMaker coffeeMaker
= objectGraph.get(CoffeeMaker.class);
coffeeMaker.brew();
}
}
Build the Graph

43. Neat features
• Lazy<T>
• Module overrides
• Multibindings

44. class GridingCoffeeMaker {
@Inject Lazy<Grinder> lazyGrinder;
public void brew() {
while (needsGrinding()) {
// Grinder created once and cached.
Grinder grinder = lazyGrinder.get()
grinder.grind();
}
}
}
Lazy<T>

45. @Module(
includes = DripCoffeeModule.class,
injects = CoffeeMakerTest.class,
overrides = true
)
static class TestModule {
@Provides @Singleton Heater provideHeater() {
return Mockito.mock(Heater.class);
}
}
Module Overrides

46. @Module
class TwitterModule {
@Provides(type=SET) SocialApi provideApi() {
...
}
}
@Module
class GooglePlusModule {
@Provides(type=SET) SocialApi provideApi() {
...
}
}
...
@Inject Set<SocialApi>
Multibindings

47. •Dagger
–Motivation
–Using Dagger
–Inside Dagger

48. Graphs!

49. Creating Graphs
• Compile time
– annotation processor
• Runtime
– generated code loader
– reflection

50. Using Graphs
• Injection
• Validation
• Graphviz!

51. But how?
• Bindings have names like
“com.squareup.geo.LocationMonitor”
• Bindings know the names of their
dependencies, like
“com.squareup.otto.Bus”

52. final class CoffeeMaker$InjectAdapter extends Binding<CoffeeMaker> {
private Binding<Heater> f0; private Binding<Pump> f1;
public CoffeeMaker$InjectAdapter() {
super("coffee.CoffeeMaker", ...);
}
public void attach(Linker linker) {
f0 = linker.requestBinding("coffee.Heater", coffee.CoffeeMaker.class);
f1 = linker.requestBinding("coffee.Pump", coffee.CoffeeMaker.class);
}
public CoffeeMaker get() {
coffee.CoffeeMaker result = new coffee.CoffeeMaker();
injectMembers(result);
return result;
}
public void injectMembers(CoffeeMaker object) {
object.heater = f0.get();
object.pump = f1.get();
}
public void getDependencies(Set<Binding<?>> bindings) {
bindings.add(f0);
bindings.add(f1); }
}

53. Validation
• Eager at build time
• Lazy at runtime

54. dagger-compiler
(cc) creative commons from flickr.com/photos/discover-central-california/8010906617

55. Built into javac
Foolishly easy to use. Just put dagger-compiler on your
classpath!
javax.annotation.processing

56. It’s a hassle
(for us)
• Coping with prebuilt .jar files
• Versioning
• Testing

57. ... and it’s limited
(for you)
• No private or final field access
• Incremental builds are imperfect
• ProGuard

58. ... but it’s smoking fast!
(for your users)
• Startup time for Square Wallet on
one device improved from ~5
seconds to ~2 seconds

59. Different Platforms are Different
• HotSpot
• Android
• GWT

60. HotSpot:
Java on the Server
• The JVM is fast
• Code bases are huge

61. Android
• Battery powered
• Garbage collection causes jank
• Slow reflection, especially on older devices
• Managed lifecycle

62. GWT
• Code size really matters
• Compiler does full-app optimizations
• No reflection.
github.com/tbroyer/sheath

63. API Design
in the GitHub age
Forking makes it easy to stay small & focused

64. public @interface Inject {}
public @interface Named {
String value() default "";
}
public interface Provider {
T get();
}
public @interface Qualifier {}
public @interface Scope {}
public @interface Singleton {}
javax.inject

65. public interface Lazy<T> {
T get();
}
public interface MembersInjector<T> {
void injectMembers(T instance);
}
public final class ObjectGraph {
public static ObjectGraph create(Object... modules);
public ObjectGraph plus(Object... modules);
public void validate();
public void injectStatics();
public <T> T get(Class type);
public <T> T inject(T instance);
}
public @interface Module {
Class[] injects() default { };
Class[] staticInjections() default { };
Class[] includes() default { };
Class addsTo() default Void.class;
boolean overrides() default false;
boolean complete() default true;
boolean library() default true;
}
public @interface Provides {
enum Type { UNIQUE, SET }
Type type() default Type.UNIQUE;
}
dagger

66. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

67. PORTABLE CONTROL OF DNS CLOUDS

68. @Provides
@Singleton
Route53 route53(Feign feign,
Route53Target target) {
return feign.newInstance(target);
}
Dependencies are
HTTP Targets

69. Portable
implementations
class Route53ZoneApi implements ZoneApi {
@Inject Route53 route53;
...
}

70. •Introduction
•Guice
•Guice at Netflix
•Dagger
•Dagger at Netflix
•Wrapping up

71. • Still the best choice for many apps
• Broad ecosystem and stable core
• May soon be able to mix & match with
Dagger
Guice

72. • Great for libraries
• Extension averse, feature conservative
• Friendly forks
Dagger

73. Takeaway
Dagger is a leaner version of Guice, suitable for libraries.
Fork-friendly doesn’t mean don’t collaborate.
http://square.github.io/dagger/
https://groups.google.com/forum/#!forum/dagger-discuss
http://www.linkedin.com/in/adrianforrestcole
@adrianfcole #netflixoss