Argo源码阅读（三）：Google-guice依赖注入框架

在Argo中用到了Google-guice依赖注入框架：http://code.google.com/p/google-guice/

Google-guice 依赖注入框架主要由@Inject注解、AbstractModule基类组成

//google code上的例子

RealBillingService类构造时依赖CreditCardProcessor和TransactionLog接口，添加@Inject注解后将由Guice调用RealBillingService构造器。

class
RealBillingService implements
BillingService {

private finalCreditCardProcessor processor;

private finalTransactionLog transactionLog;

@Inject

RealBillingService(CreditCardProcessor processor,

TransactionLog transactionLog){

this.processor= processor;

this.transactionLog= transactionLog;

}

@Override

public Receipt chargeOrder(PizzaOrder order,CreditCard
creditCard){

...

}

}

AbstractModule构建Guice的object-graph，重载Configure方法实现接口和实现类的绑定。

public class BillingModule extends AbstractModule {
@Override
protected void configure() {

/*
* This tells Guice that whenever it sees a dependency on a TransactionLog,
* it should satisfy the dependency using a DatabaseTransactionLog.
*/
bind(TransactionLog.class).to(DatabaseTransactionLog.class);

/*
* Similarly, this binding tells Guice that when CreditCardProcessor is used in
* a dependency, that should be satisfied with a PaypalCreditCardProcessor.
*/
bind(CreditCardProcessor.class).to(PaypalCreditCardProcessor.class);
}
}

由此也可以看出@Inject 和 bind是一起出现的

用Module子类创建新的Guice注解器实例

public static void main(String[] args) {
/*
* Guice.createInjector() takes your Modules, and returns a new Injector
* instance. Most applications will call this method exactly once, in their
* main() method.
*/
Injector injector = Guice.createInjector(new BillingModule());

/*
* Now that we've got the injector, we can build objects.
*/
RealBillingService billingService = injector.getInstance(RealBillingService.class);
...
}

Argo中的注入

public class Argo {

public ArgoDispatcher init(ServletContext servletContext,
GroupConvention groupConvention) {
…

List<Module> modules = Lists.newArrayList();
modules.add(new ArgoModule(this));

Module groupModule = groupConvention.group().module();
if (null != groupModule)
modules.add(groupModule);

Module projectModule = groupConvention.currentProject().module();
if (null != projectModule)
modules.add(projectModule);

servletContext.log("preparing an injector");
this.injector = buildInjector(modules);
servletContext.log("injector completed");

…
}

private Injector buildInjector(List<Module> modules) {
return Guice.createInjector(modules);
}

public class ArgoModule extends AbstractModule {

@Override
protected void configure() {

bind(ServletRequest.class).to(HttpServletRequest.class);
bind(ServletResponse.class).to(HttpServletResponse.class);

bind(BeatContext.class)
.annotatedWith(ArgoSystem.class)
.to(DefaultBeatContext.class);

bind(ActionResult.class)
.annotatedWith(Names.named("HTTP_STATUS=404"))
.toInstance(StatusCodeActionResult.defaultSc404);

bind(ActionResult.class)
.annotatedWith(Names.named("HTTP_STATUS=405"))
.toInstance(StatusCodeActionResult.defaultSc405);

bind(Action.class).annotatedWith(StaticActionAnnotation.class)
.to(StaticFilesAction.class);

bind(ClientContext.class).to(DefaultClientContext.class);
bind(Model.class).to(DefaultModel.class);

bind(MultipartConfigElement.class)
.toProvider(DefaultMultipartConfigElementProvider.class)
.in(Singleton.class);

// bind all controllers.
for (Class<? extends ArgoController> clazz : argo.getControllerClasses())
bind(clazz).in(Singleton.class);
}
｝

由此可见，Argo中的init方法首先构造Module实例集合，然后调用Guice的CreateInjector方法绑定对应的接口和实现类。

argo.getControllerClasses()中的Module应该是在Argo框架注解过的集合。