如何在Guice中获取动态类型/动态构建的ParameterizedType的实例 [英] How to get instance for dynamic type/dynamically built ParameterizedType in Guice

问题描述

考虑到注入器，我想知道如何检索某些参数化类型的特定实例(但我自己没有Type).让我解释一下自己:

Given an injector, I am wondering how I can retrieve a specific instance of some parameterized type (but I don't have the Type itself). Let me explain myself:

想象一下您已经进行了以下绑定:

Imagine that you have made the following bindings:

• List<Apple>绑定到ArrayList<Apple>
• Set<Pears>绑定到HashSet<Pear>
• 等...，用于Fruit的其他Collection.

• List<Apple> bound to ArrayList<Apple>
• Set<Pears> bound to HashSet<Pear>
• etc... for other Collection of Fruit.

现在我有一个Fruit fruit实例，我想检索适当的Collection实例.我该如何实现?

Now I have a Fruit fruit instance and I would like to retrieve the appropriate Collection instance. How can I achieve this?

这是一个小的工作片段，其中用代码说明了我的所有解释:

Here is a small working snippet that illustrates with code all my explanations:

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;

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

public class TestGuiceDynamicType {
    public static interface Fruit {

    }

    public static class Apple implements Fruit {

    }

    public static class Pear implements Fruit {

    }

    public static class FruitModule extends AbstractModule {
        @Override
        protected void configure() {
            bind(new TypeLiteral<Collection<Apple>>() {

            }).to(new TypeLiteral<ArrayList<Apple>>() {
            });
            bind(new TypeLiteral<Collection<Pear>>() {

            }).to(new TypeLiteral<HashSet<Pear>>() {
            });

        }
    }


    private <T extends Fruit> static void addFruit(Injector injector, T fruit) {
        Collection<T> collection  = ????? // What to do here to get the appropriate collection
        collection.add(fruit);
    }

    public static void main(String[] args) {
        Injector injector = Guice.createInjector(new FruitModule());
        Collection<Apple> appleCollection = injector.getInstance(Key.get(new TypeLiteral<Collection<Apple>>() {

        }));
        appleCollection.add(new Apple());
        addFruit(injector, new Pear())
    }
}

推荐答案

好的，我最终找到了解决方法:

OK, I eventually found the solution:

private static <T extends Fruit> void addFruit(Injector injector, T fruit) {
    Collection<T> collection = (Collection<T>) injector.getInstance(Key.get(Types.newParameterizedType(Collection.class,
            fruit.getClass())));
    collection.add(fruit);
}

关键是使用com.google.inject.util.Types类的Types.newParameterizedType().

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