java - 如何将接口(interface)与通用类的实现绑定(bind)？

Question

[Guice 4.0]

我想要一个泛型类的接口(interface)，并通过 Guice 在依赖注入(inject)中使用它。对于下面列出的代码，我收到以下错误:

Exception in thread "main" com.google.inject.CreationException: Unable to create injector, see the following errors:

1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
  at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:14)
  at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)

--

public class Class1<T1 extends Number, T2 extends Number>
    implements InterfClass1<T1, T2> {
    public static final String ANNOT1 = "ANNOT1";
    public static final String ANNOT2 = "ANNOT2";
    private T1 t1;
    private T2 t2;
    // for the factory
    @AssistedInject
    public Class1(
            @Assisted(Class1.ANNOT1) T1 t1,
            @Assisted(Class1.ANNOT2) T2 t2
            ) {
        this.t1 = t1;
        this.t2 = t2;
    }
    public T1 getT1() {
        return t1;
    }
    public T2 getT2() {
        return t2;
    }
}


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

        bind(new TypeLiteral<InterfClass1<Integer, Integer>>(){})
            .to(new TypeLiteral<Class1<Integer, Integer>>(){});
    }

    public static void main(String[] args) {
        Injector inj = Guice.createInjector(new Module());
    }
}

什么原因导致此错误？

编辑后

让我们添加工厂并修改模块(从模块中删除 InterfClass1 接口(interface)):

public interface Class1Factory<T1 extends Number, T2 extends Number> {
    public Class1<T1, T2> createClass1(
            @Assisted(Class1.ANNOT1) T1 t1,
            @Assisted(Class1.ANNOT2) T2 t2
            );
}

public class Module extends AbstractModule {
    @Override
    protected void configure() {
        install(new FactoryModuleBuilder()
            .build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
    }
    public static void main(String[] args) {
        Injector inj = Guice.createInjector(new Module());
        Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
        f.createClass1(10, 11.0);
    }
}

效果很好!

现在让我们合并界面:

public class Module extends AbstractModule {
    @Override
    protected void configure() {
        bind(new TypeLiteral<InterfClass1<Integer, Double>>(){})
            .to(new TypeLiteral<Class1<Integer, Double>>(){});
        install(new FactoryModuleBuilder()
            .build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
    }
    public static void main(String[] args) {
        Injector inj = Guice.createInjector(new Module());
        Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
        f.createClass1(10, 11.0);
    }
}

我们得到:

1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
  at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:15)
  at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)

好吧，不管错误如何，我们也更改工厂:

public interface Class1Factory<T1 extends Number, T2 extends Number> {
    public InterfClass1<T1, T2> createClass1(
            @Assisted(Class1.ANNOT1) T1 t1,
            @Assisted(Class1.ANNOT2) T2 t2
            );
}

我们得到:

1) Could not find a suitable constructor in com.ulmon.fsqtransit.guicetest.Class1. Classes must have either one (and only one) constructor annotated with @Inject or a zero-argument constructor that is not private.
  at com.ulmon.fsqtransit.guicetest.Class1.class(Class1.java:15)
  at com.ulmon.fsqtransit.guicetest.Module.configure(Module.java:14)

2) com.ulmon.fsqtransit.guicetest.InterfClass1<java.lang.Integer, java.lang.Double> is an interface, not a concrete class.  Unable to create AssistedInject factory.
  while locating com.ulmon.fsqtransit.guicetest.InterfClass1<java.lang.Integer, java.lang.Double>
  at com.ulmon.fsqtransit.guicetest.Class1Factory.createClass1(Class1Factory.java:1)

但是，如果我删除模块中接口(interface)和类之间的关系并将此关系添加到工厂的规范中，则不会出现错误:

public class Module extends AbstractModule {
    @Override
    protected void configure() {
        install(new FactoryModuleBuilder()
            .implement(new TypeLiteral<InterfClass1<Integer, Double>>(){}
                , new TypeLiteral<Class1<Integer, Double>>(){})
            .build(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
    }
    public static void main(String[] args) {
        Injector inj = Guice.createInjector(new Module());
        Class1Factory f = inj.getInstance(Key.get(new TypeLiteral<Class1Factory<Integer, Double>>(){}));
        f.createClass1(10, 11.0);
    }
}

效果很好!

为什么 Guice 有这种奇怪的行为？为什么无论工厂如何，我都无法将接口(interface)与实现类关联起来？

Answer 1

我无法确切地弄清楚您想要做什么，但在我看来，您实际上并没有尝试创建 AssistedInject 工厂，因为您还没有为工厂创建接口(interface)。在这种情况下，您根本不需要使用 @Assisted 参数。您的构造函数应如下所示(对该类没有其他更改):

@Inject
public Class1(
        @Named(Class1.ANNOT1) T1 t1,
        @Named(Class1.ANNOT2) T2 t2
        ) {

然后，指定模块中的绑定(bind)。您必须明确告诉 Guice 为参数注入(inject)什么以及您指定的注释:

@Override
protected void configure() {
    bind(new TypeLiteral<InterfClass1<Integer, Integer>>(){})
        .to(new TypeLiteral<Class1<Integer, Integer>>(){});
    bind(Integer.class)
        .annotatedWith(Names.named(Class1.ANNOT1))
        .toInstance(5);
    bind(Integer.class)
        .annotatedWith(Names.named(Class1.ANNOT2))
        .toInstance(15);
}

然后，我们可以像这样运行它:

public static void main(String[] args) {
    Injector inj = Guice.createInjector(new Module());
    InterfClass1<Integer, Integer> interf =
        inj.getInstance(Key.get(new TypeLiteral<InterfClass1<Integer, Integer>>(){}));
    System.out.println(interf.getClass());
    System.out.println("T1: " + interf.getT1() + " T2: " + interf.getT2());
}

正如您在运行它时所看到的，它将注入(inject)一个 Class 实现，并指定两个参数:

class guice.Class1
T1: 5 T2: 15

<小时/>

如果您尝试使用 AssistedInject 构建 Class1 对象工厂，则由于您指定 Generit 类型参数的方式，这会变得更加困难。不幸的是，你不能inject a generic factory using AssistedInject in the normal way ，这会变得更加困难，因为您的 Class1 实现需要 T1 extends Number，但您的接口(interface)可以是您想要的任何 T1。这意味着您的工厂必须将其接收的输入参数的类型限制为 Number 的子类；换句话说，您的工厂不能只创建它想要的任何 InterfClass1，它只能创建具有正确输入参数的实例。

希望答案的前半部分就是您想要做的。如果不是，我们需要有关您的用例的更多信息才能回答此问题。