注入仿制药与Guice [英] Injecting generics with Guice

问题描述

我正在努力迁移一个小型项目，用Guice替代一些工厂（这是我第一个Guice试用版）。但是，当我试图注入仿制药物时，我被困住了。我设法提取一个小的玩具示例，有两个类和一个模块：

  import com.google.inject.Inject; 
 
 public class Console< T> {
 private final StringOutput< T>出; 
 @Inject 
 public Console（StringOutput< T> out）{
 this.out = out; 
} 
 public void print（T t）{
 System.out.println（out.converter（t））; 
} 
} 
 
 public class StringOutput< T> {
 public String converter（T t）{
 return t.toString（）; 
} 
} 
 
 import com.google.inject.AbstractModule; 
 import com.google.inject.Guice; 
 import com.google.inject.Injector; 
 import com.google.inject.TypeLiteral; 
 
 
 public class MyModule extends AbstractModule {
 
 @Override 
 protected void configure（）{
 bind（StringOutput.class）; 
 bind（Console.class）; 
} 
 
 public static void main（String [] args）{
注入器注入= Guice.createInjector（new MyModule（））; 
 StringOutput<整数> out = injector.getInstance（StringOutput.class）; 
 System.out.println（out.converter（12））; 
控制台< Double> cons = injector.getInstance（Console.class）; 
 cons.print（123.0）; 
} 
 
} 
  

当我运行这个例子，所有我得到的是：

线程中的异常maincom.google.inject.CreationException：Guice创建错误：

  1）playground.StringOutput< T>不能用作钥匙;没有完全指定。 
在playground.MyModule.configure（MyModule.java:15）
 
 1错误
在com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist（Errors.java:354） 
 com.google.inject.InjectorBuilder.initializeStatically（InjectorBuilder.java:152）
 com.google.inject.InjectorBuilder.build（InjectorBuilder.java:105）
在com.google .inject.Guice.createInjector（Guice.java:92）
  

我尝试寻找错误消息，但没有找到任何有用的提示。进一步在Guice FAQ上，我绊倒了一个关于如何注射仿制药的问题。我试图在 configure 方法中添加以下绑定：

  bind （new TypeLiteral< StringOutput< Double>>（）{}）toInstance（new StringOutput< Double>（））; 
  

但没有成功（同样的错误信息）。

有人可以向我解释错误信息，并提供一些提示？谢谢。

解决方案

我认为你看到的具体问题可能是因为 bind .class）语句。它也应该使用 TypeLiteral 。或者，你可以绑定这两个，JIT绑定将会为你照顾，因为这里涉及的所有类型都是具体的类。

此外，你应该检索控制台与：

 控制台< Double> cons = 
 inject.getInstance（Key.get（new TypeLiteral< Console< Double>>（）{}））; 
  

编辑：你不需要绑定到一个实例，只因为您正在使用 TypeLiteral 。你可以这样做：

  bind（new TypeLiteral< Console< Double>>（）{}）; 
  

当然，就像上面所说的，你可以跳过这个例子，然后检索<$ c基于 TypeLiteral 和绑定的键从注入器中获取$ c>控制台将是隐含的。

I am trying to migrate a small project, replacing some factories with Guice (it is my first Guice trial). However, I am stuck when trying to inject generics. I managed to extract a small toy example with two classes and a module:

import com.google.inject.Inject;

public class Console<T> {
  private final StringOutput<T> out;
  @Inject
  public Console(StringOutput<T> out) {
    this.out = out;
  }
  public void print(T t) {
    System.out.println(out.converter(t));
  }
}

public class StringOutput<T> {
  public String converter(T t) {
    return t.toString();
  }
}

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Injector;
import com.google.inject.TypeLiteral;


public class MyModule extends AbstractModule {

  @Override
  protected void configure() {
    bind(StringOutput.class);
    bind(Console.class);
  }

  public static void main(String[] args) {
    Injector injector = Guice.createInjector( new MyModule() );
    StringOutput<Integer> out = injector.getInstance(StringOutput.class);
    System.out.println( out.converter(12) );
    Console<Double> cons = injector.getInstance(Console.class);
    cons.print(123.0);
  }

}

When I run this example, all I got is:

Exception in thread "main" com.google.inject.CreationException: Guice creation errors:

1) playground.StringOutput<T> cannot be used as a key; It is not fully specified.
  at playground.MyModule.configure(MyModule.java:15)

1 error
    at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:354)
    at com.google.inject.InjectorBuilder.initializeStatically(InjectorBuilder.java:152)
    at com.google.inject.InjectorBuilder.build(InjectorBuilder.java:105)
    at com.google.inject.Guice.createInjector(Guice.java:92)

I tried looking for the error message, but without finding any useful hints. Further on the Guice FAQ I stumble upon a question about how to inject generics. I tried to add the following binding in the configure method:

bind(new TypeLiteral<StringOutput<Double>>() {}).toInstance(new StringOutput<Double>());

But without success (same error message).

Can someone explain me the error message and provide me some tips ? Thanks.

解决方案

I think the specific issue you're seeing is probably because of the bind(Console.class) statement. It should use a TypeLiteral as well. Or, you could just bind neither of those and JIT bindings will take care of it for you since both of the types involved here are concrete classes.

Additionally, you should retrieve the Console with:

Console<Double> cons = 
   injector.getInstance(Key.get(new TypeLiteral<Console<Double>>(){}));

Edit: You don't need to bind to an instance just because you're using a TypeLiteral. You can just do:

bind(new TypeLiteral<Console<Double>>(){});

Of course, like I said above you could just skip that in this case and retrieve the Console from the injector using a Key based on the TypeLiteral and the binding would be implicit.

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