Guice tutorial

GIN
A basic tutorial
by

anhquan.de

What the heck is Google GIN?

• GIN = GWT INjection
• Guice brings automatic dependency injection to server side
code, while GIN is for client-side code.
• GIN is built on top of Guice and uses (a subset of) Guice's
binding language


binding language

GWT client-side
code

GIN


binding language

GWT client-side GWT server-side
code code

GIN Guice

This tutorial shows you

How to use GIN ?

5 Steps to remember
1. Design the application with Interfaces IA,IB,…

5 Steps to remember
2. Create concrete classes AImpl, BImpl,… to implement interfaces IA,IB,…
Remember: use @Inject to mark the non-default constructor.

5 Steps to remember
3. Create AppClientModule to configure which implementation is bound to which interface

5 Steps to remember
4. Create interface AppGinjector with the AppClientModule in the annotation @GinModules.

@GinModules({AppClientModule.class, other modules …})

5 Steps to remember
4. Create interface AppGinjector with the AppClientModule in the annotation @GinModules.

@GinModules({AppClientModule.class, other modules …})

5. Generate code for AppGinjector and use it

private final AppGinjector injector = GWT.create(AppGinjector.class);

AppPresenter aPres = injector.getAppPresenter();
aPres.bind();

RootPanel.get().add(aPres.getDisplay().asWidget());

Step 1: Design an Interface

public class ConfigPresenter extends WidgetPresenter<ConfigPresenter.Display>{

public interface Display extends NameAwareWidgetDisplay, WidgetDisplay {
public HasClickHandlers getSaveClick();
public void updateConfig(Config config);
}
…
}

Step 1: Design an Interface

public class ConfigPresenter extends WidgetPresenter<ConfigPresenter.Display>{

public interface Display extends NameAwareWidgetDisplay, WidgetDisplay {
public HasClickHandlers getSaveClick();
public void updateConfig(Config config);
}
…
}

For gwt-dispatch developers:
Normally, we create a Display interface as an inner interface of
a Presenter class

Step 2: Implement the interface

public class ConfigView extends Composite implements ConfigPresenter.Display {

private VerticalPanel panel = new VerticalPanel();

private AppConstants constants;

@Inject
public ConfigView(AppConstants constants, AppMessages messages) {
this.constants = constants;
panel.addStyleName(AppCSS.C_config_container);
panel.add(new HTML("<h1>Config view: comming soon<h1>"));
initWidget(panel);
}
…
}

Step 2: Implement the interface
If the class has no default constructor, then a @Inject annotation is required. Otherwise, you will get
a RuntimeException (“No @Inject or default constructor found for class …. ”)

public class ConfigView extends Composite implements ConfigPresenter.Display {

private VerticalPanel panel = new VerticalPanel();

private AppConstants constants;

@Inject
public ConfigView(AppConstants constants, AppMessages messages) {
this.constants = constants;
panel.addStyleName(AppCSS.C_config_container);
panel.add(new HTML("<h1>Config view: comming soon<h1>"));
initWidget(panel);
}
…
}

Step 3: Create class AppClientModule

public class AppClientModule extends AbstractPresenterModule {

@Override
protected void configure() {
bind(EventBus.class).to(DefaultEventBus.class).in(Singleton.class);
bind(PlaceManager.class).to(AppPlaceManager.class);
bindPresenter(LoginPresenter.class, LoginPresenter.Display.class, LoginView.class);
bindPresenter(MainPresenter.class, MainPresenter.Display.class, MainView.class);
bindPresenter(AppPresenter.class, AppPresenter.Display.class, AppView.class);
bind(LoginPresenterPlace.class).in(Singleton.class);
bind(ContactsPresenterPlace.class).in(Singleton.class);
…
bind(LoginPresenter.class).in(Singleton.class);
bind(LoginPresenter.Display.class).to(LoginView.class);

}
}

Step 3: Create class AppClientModule

public class AppClientModule extends AbstractPresenterModule {

@Override
protected void configure() {
bind(EventBus.class).to(DefaultEventBus.class).in(Singleton.class);
bind(PlaceManager.class).to(AppPlaceManager.class);
bindPresenter(LoginPresenter.class, LoginPresenter.Display.class, LoginView.class);
bindPresenter(MainPresenter.class, MainPresenter.Display.class, MainView.class);
bindPresenter(AppPresenter.class, AppPresenter.Display.class, AppView.class);
bind(LoginPresenterPlace.class).in(Singleton.class);
bind(ContactsPresenterPlace.class).in(Singleton.class);
…
bind(LoginPresenter.class).in(Singleton.class);
bind(LoginPresenter.Display.class).to(LoginView.class);

}
} Don’t need to bind LoginPresenter and LoginPresenter.Display
Because they are already “bind” above in the bindPresenter(…)

See the implementation of the bindPresenter() in the next slide …

Note: Implementation of bindPresenter()

public abstract class AbstractPresenterModule extends AbstractGinModule {

protected <D extends Display> void bindPresenter( Class<? extends Presenter> presenter,
Class<D> display, Class<? extends D> displayImpl )
{
bind( presenter ).in( Singleton.class );
bindDisplay( display, displayImpl );
}

protected <D extends Display> void bindDisplay( Class<D> display, Class<? extends D>
displayImpl )
{
bind( display ).to( displayImpl );
}
…
}



{
}

displayImpl )
{
}
…
}

DisplayImpl class is bound to Display interface

Presenter is bound as Singleton. It means there is no new instance
created when you invoke AppGinjector.getPresenter()

{
}

displayImpl )
{
}
…
}

DisplayImpl class is bound to Display interface

Step 4: Define AppGinjector interface

@GinModules({ClientDispatchModule.class,AppClientModule.class})
public interface AppGinjector extends Ginjector {
public AppPresenter getAppPresenter();
public PlaceManager getPlaceManager();
public EventBus getEventBus();
}


List of modules. Each module class contains only one
configure() method to specify
which implementation is bound to which interface.

}



A helper module provided by gwt-dispatch
(just ignore it for now)
}



public PlaceManager getPlaceManager(); You create it
}
in step 3!



}
in step 3!

Use whatever name you want!



}
in step 3!

Use whatever name you want!

Return type is important. Injector will return the instance
basing on type.

Step 5: Using Injector in the EntryPoint

public class App implements EntryPoint{


public void onModuleLoad() {

aPres.bind();


PlaceManager placeManager = injector.getPlaceManager();

placeManager.fireCurrentPlace();
}

}

GWT generates the implementation
of AppGinjector at compile time



aPres.bind();



}

}

GWT generates the implementation
of AppGinjector at compile time



aPres.bind();



}

}

Here are all Interfaces. Their implementations are injected by GIN.
But which implementation is bound to which Interface? => See AppClientModule .configure()

Learn more
Articles:
• Google's MVP tutorial
• Best Practices For Architecting Your GWT App session

Projects:
• Project google-gin
• Project google-guice
• Project gwt-dispatch
• Project gwt-presenter
• Project gwt-platform
• A project implement MVP patterns based on gwt-dispatch, gin, guice
• Apache Hupa – a GWT based webmail (using maven+junit+eclipse, gwt-dispatch, gwt-
presenter, gin, guin). Highly recommended!
• TeampScape – Another tutorial projects about gwt+gae, gwt-dispatch, gwt-presenter,
datastore/jdo

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