This document provides an overview of Google Guice, an open source Java framework for dependency injection. It discusses key Guice concepts like dependency injection, bindings, providers, and scopes. It also covers advanced topics such as aspect-oriented programming with Guice, integration with other frameworks like Spring, and using Guice in servlets. The goal of Guice is to simplify dependency management and increase testability by removing hard-coded dependencies.

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 ?