如何避免在使用guice时使用inject.createInstance（）全部位置？

问题描述

有一些我不知道的是什么：根据我迄今为止所读到的内容，我应该在我的引导类中使用Injector（在一个独立的应用程序中，这通常是主要的）方法），如下面的示例（取自guice文档）：

  public static void main（String [] args ）{
 / * 
 * Guice.createInjector（）接收您的模块，并返回一个新的Injector 
 *实例。大多数应用程序将在
 * main（）方法中调用此方法一次。 
 * / 
注射器喷射器= Guice.createInjector（新的BillingModule（））; 
 
 / * 
 *现在我们有了注入器，我们可以构建对象。 
 * / 
 RealBillingService billingService = injector.getInstance（RealBillingService.class）; 
 ... 
} 
  

但是，如果不是所有我需要的对象可以在启动时创建吗？也许我想在应用程序运行时响应一些用户交互？我不必将注射器保持在某处（例如，作为静态变量），然后在需要创建新对象时调用inject.getInstance（SomeInterface.class）？

当然，将呼叫到Injector.getInstance（）遍布整个地方似乎是不可取的。

我在这里遇到什么问题？

解决方案

是的，您基本上只能使用Injector创建获取根对象的实例。其余的应用程序不应接触Guice-Container。如您所知，您仍然需要在需要时创建一些对象。有不同的方法来做，每个都适合不同的需求。

注入提供者
是Guice的界面。它允许您请求一个新的对象实例。该对象将使用Guice创建。例如。

  class MyService {
 private Provider< Transaction> transactionProvider; 
 public MainGui（Provider< Transaction> transactionProvider）{
 this.transactionProvider = transactionProvider; 
} 
 
 public void actionStarted（）{
事务事务= transactionProvider.get（）; 
} 
  

建立工厂
通常你需要某种工厂。该工厂使用一些注入的服务和一些参数，并为您创建一个新的对象。然后你使用这个工厂的新实例。然后你注入该工厂并使用它。使用 -extension

也有助于此

我认为这两种可能性，您很少需要使用Guice-Injector本身。然而，有时仍然适合使用喷射器本身。然后您可以将注射器注入到组件中。

There's something I just don't get about guice: According to what I've read so far, I'm supposed to use the Injector only in my bootstrapping class (in a standalone application this would typically be in the main() method), like in the example below (taken from the guice documentation):

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);
    ...
  }

But what if not all Objects I ever need can be created during startup? Maybe I want to respond to some user interaction when the application is running? Don't I have to keep my injector around somewhere (e.g. as a static variable) and then call injector.getInstance(SomeInterface.class) when I need to create a new object?

Of course spreading calls to Injector.getInstance() all over the place seems not to be desirable.

What am I getting wrong here?

解决方案

Yes, you basically only should use the Injector to create get the instance for the root-object. The rest of the application shouldn't touch the Guice-Container. As you've noticed, you still need to create some objects when required. There are different approaches for doing that, each suitable for different needs.

Inject a ProviderProvider is a interface from Guice. It allows you to request a new instance of a object. That object will be created using Guice. For example.

 class MyService{
     private Provider<Transaction> transactionProvider;
     public MainGui(Provider<Transaction> transactionProvider){
         this.transactionProvider = transactionProvider;
     }

     public void actionStarted(){
         Transaction transaction = transactionProvider.get();
     }

Build a FactoryOften you need some kind of factory. This factory uses some injected services and some parameters and creates a new object for you. Then you use this factory for new instances. Then you inject that factory and use it. There also help for this with the AssistedInject-extension

I think with these two possibilities you rarely need to use the Guice-Injector itself. However sometimes is still appropriate to use the injector itself. Then you can inject the Injector to a component.

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