1. Google Guice
Kirill Afanasjev
Software Architect
jug.lv
Riga, Latvia

2. Overview
 Dependency Injection
 Why Guice
 Getting Guice
 Using Guice
 Advanced Guice

3. Code without DI
public void sendButtonClicked() {
String text = messageArea.getText();
Validator validator = new MailValidator();
validator.validate(text);
MailSender sender = new MailSender();
sender.send(text);
}

4. Using factories
public void sendButtonClicked() {
String text = messageArea.getText();
Validator validator = ValidatorFactory.get();
validator.validate(text);
MailSender sender = SenderFactory.get();
sender.send(text);
}

5. Testable now
public void testSendButton() {
MockSender mockSender = new MockSender();
SenderFactory.setInstance(mockSender);
MailForm form = new MailForm();
form.getMessageArea().setText("Some text");
form.sendButtonClicked();
assertEquals("Some text", mockSender.getSentText());
SenderFactory.clearInstance();
}

6. Well, not really
public void testSendButton() {
MockSender mockSender = new MockSender();
SenderFactory.setInstance(mockSender);
try {
MailForm form = new MailForm();
form.getMessageArea().setText("Some text");
form.sendButtonClicked();
assertEquals("Some text", mockSender.getSentText());
} finally {
SenderFactory.clearInstance();
}
}

7. Dependency injection
private Validator validator;
private MailSender mailSender;
public MailForm(Validator validator, MailSender mailSender) {
this.validator = validator;
this.mailSender = mailSender;
}
public void sendButtonClicked() {
…..

8. Testing now
public void testSendButton() {
MockSender mockSender = new MockSender();
Validator validator = new Validator();
MailForm form = new MailForm(validator, mockSender);
form.getMessageArea().setText("Some text");
form.sendButtonClicked();
assertEquals("Some text", mockSender.getSentText());
}

9. Why DI frameworks
 Avoid boilerplate code
 AOP
 Integrate your DI with http session/request,
data access APIs, e.t.c
 Separate dependencies configuration from
code
 Makes life easier

10. What is Guice
 Open source dependency injection framework
 License : Apache License 2.0
 Developer : Google

11. Why Guice
 Java API for configuration
 Easier to use
 Line numbers in error messages
 Less overhead
 Less features, too
 DI in GWT client-side code (using GIN)

12. Getting Guice
 http://code.google.com/p/google-guice/
 http://mvnrepository.com/
 Small – 865 KB
 Version without AOP, suitable for Android –
470KB
 Lacks fast reflection and line numbers in errors

13. Dependency injection with Guice
private Validator validator;
private MailSender mailSender;
@Inject
public MailForm(Validator validator, MailSender mailSender) {
this.validator = validator;
this.mailSender = mailSender;
}

14. Creating instance of MailForm
Injector injector =
Guice.createInjector(new YourAppModule());
MailForm mailForm = injector.getInstance(MailForm.class);

15. Bindings
public class YourAppModule extends AbstractModule {
protected void configure() {
bind(MailService.class).to(MailServiceImpl.class);
bind(Validator.class).to(ValidatorImpl.class);
}
}

16. Providers
public class YourAppModule extends AbstractModule {
protected void configure() {
bind(Validator.class).to(ValidatorImpl.class);
}
@Provides
MailService getMailService() {
MailService service = new MailService();
return service;
}
….

17. Injecting fields
@Inject
private Validator validator;
@Inject
private MailSender mailSender;
public MailForm() {
}

18. Injecting with setter methods
private Validator validator;
public MailForm() {
}
@Inject
public void setValidator(Validator validator) {
this.validator = validator;
}

19. Optional injection
 Inject(optional=true)
 Ignores values for which no bindings are
avalaible
 Possible with setter methods only

20. Bind instance
protected void configure() {
bind(Integer.class).annotatedWith(ThreadCount.cla
ss).toInstance(4);
}
..
@ThreadCount
int threadCount;
 IDE autocomplete, find usages e.t.c

21. Two implementations
protected void configure() {
bind(Validator.class).to(ValidatorImpl.class);
bind(Validator.class).to(StrictValidatorImpl.class);
}

22. Two implementations
Exception in thread "main" com.google.inject.CreationException:
Guice configuration errors:
1) Error at lv.jug.MailService.configure(YourAppModule.java:12):
A binding to lv.jug.MailService was already configured at
lv.jug.YourAppModule.configure(YourAppModule.java:11)

23. Two implementations
protected void configure() {
bind(Validator.class).to(ValidatorImpl.class);
bind(Validator.class)
.annotatedWith(Strict.class)
.to(StrictValidatorImpl.class);
}
….
@Inject
public MailForm(@Strict Validator validator) {
this.validator = validator;
}

24. Binding annotation
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.PARAMETER})
@BindingAnnotation
public @interface Strict {}

25. Implicit binding
@Inject
public MailForm(
@ImplementedBy(StrictValidator.class) Validator
Validator validator,
MailSender mailSender) {
this.validator = validator;
this.mailSender = mailSender;
}

26. Static injection
protected void configure() {
bind(Validator.class).to(ValidatorImpl.class);
requestStaticInjection(OurClass.class);
}
…
…
@Inject static Validator validator;

27. Scoping
protected void configure() {
bind(Validator.class).to(ValidatorImpl.class)
.in(Scopes.SINGLETON);
bind(MailService.class).to(MailServiceImpl.class)
.asEagerSingleton();
}

28. Multibindings
Multibinder<Plugin> pluginBinder =
Multibinder.newSetBinder(binder(), Plugin.class);
pluginBinder.addBinding().to(SomePluginImpl.class);
pluginBinder.addBinding().to(AnotherPluginImpl.class);
….
@Inject Set<Plugin> plugins

29. Grapher
 Describe the object graph in detail
 Show bindings and dependencies from several
classes in a complex application in a unified
diagram
 Generates .dot file

30. Advanced Guice
 AOP
 Warp
 Google Gin
 Spring integration
 Using guice with Servlets

31. Why AOP
 Transaction handling
 Logging
 Security
 Exception handling
 e.t.c

32. AOP
 void bindInterceptor(
Match <? super Class<?>> classMatcher,
Matcher<? super Method> methodMatcher,
MethodInterceptor... interceptors)
public interface MethodInterceptor extends
Interceptor {
Object invoke (MethodInvocation invocation) throws
Throwable
}

33. AOP
 You can not match on private and final methods
due to technical limitations in Java
 Only works for objects Guice creates

34. Warp
 http://www.wideplay.com/
 Eco-system for Google Guice
 Thin lightweight modules for Guice applications
 Persistence
 Transactions
 Servlets

35. Warp-persist
 Supports : Hibernate/JPA/Db4Objects
 Inject DAOs & Repositories
 Flexible units-of-work
 Declarative transaction management
( @Transactional )
 Your own AOP for transactions management
 @Finder(query="from Person")

36. Google Gin
 Automatic dependency injection for GWT client-
side code
 Code generation
 Little-to-no runtime overhead, compared to
manual DI
 Uses Guice binding language
 http://code.google.com/p/google-gin/

37. Spring integration
 http://code.google.com/p/guice-spring/
 @Named(”mySpringBean”)

38. JSR-330
 javax.inject
 @Inject
 @Named
 @Qualifier
 @Scope
 @Singleton
 e.t.c
 Supported by Guice, Spring, EJB

39. Using Guice with Servlets
 @RequestScoped
 @SessionScoped
 ServletModule
 serve(”/admin”).with(AdminPanelServlet.class)
 serve("*.html", "/my/*").with(MyServlet.class)
 filter(”/*”).through(MyFilter.class)
 @Inject @RequestParameters Map<String,
String[]> params;

40. Thank you
 Questions ?