关于 java：如何让 Guice 正确绑定这个泛型？

How do I make Guice bind this generic correctly?

我正在开发一个处理消息的平台，但我遇到了 Guice 绑定的问题。我编写了一个示例项目来显示我遇到的问题，这是一个如下所示的异常：

1) com.icacarealign.worker_example.PreprocessorMiddleware<MessageType> cannot be used as a key; It is not fully specified.

代码来了。

接口

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public interface Middleware {
void configure();
}

public interface PreprocessorMiddleware<MessageType> extends Middleware {
void prework(Context<MessageType> contextObj);
}

public interface PostprocessorMiddleware<MessageType> extends Middleware {
void postwork(Context<MessageType> contextObj);
}

古斯绑定

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public class MiddlewareModule<MessageType> extends AbstractModule {
private final List<Class<? extends PostprocessorMiddleware<MessageType>>> _postprocessors;
private final List<Class<? extends PreprocessorMiddleware<MessageType>>> _preprocessors;

public MiddlewareModule(
List<Class<? extends PreprocessorMiddleware<MessageType>>> preprocessors,
List<Class<? extends PostprocessorMiddleware<MessageType>>> postprocessors
) {
_preprocessors = preprocessors;
_postprocessors = postprocessors;
}

@Override
protected void configure() {
bindAllMiddleware(_preprocessors, new TypeLiteral<PreprocessorMiddleware<MessageType>>() {});
bindAllMiddleware(_postprocessors, new TypeLiteral<PostprocessorMiddleware<MessageType>>() {});
}

private <T extends Middleware> void bindAllMiddleware(List<Class<? extends T>> middleware, TypeLiteral< T > type) {
Multibinder< T > multibinder = Multibinder.newSetBinder(binder(), type);

middleware.forEach(middlewareType -> bindMiddleware(multibinder, middlewareType));
}

private <T extends Middleware> void bindMiddleware(Multibinder< T > binder, Class<? extends T> type) {
binder().bind(type).in(Singleton.class);
binder.addBinding().to(type);
}
}

主要方法

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public class Main {
public static void main(String[] args) {
List<Class<? extends PreprocessorMiddleware<Message>>> preprocessorMiddlewares = new ArrayList<>();
List<Class<? extends PostprocessorMiddleware<Message>>> postprocessorMiddlewares = new ArrayList<>();

preprocessorMiddlewares.add(ArbitraryPrepreprocessorMiddleware.class);
postprocessorMiddlewares.add(ArbitraryPostprocessorMiddleware.class);

MiddlewareModule<Message> module = new MiddlewareModule<>(preprocessorMiddlewares, postprocessorMiddlewares);

Injector injector = Guice.createInjector(module);
}
}

我做错了什么？

正如 jacobm 所描述的，您需要解决泛型问题，并且可能需要传入您要绑定的类型。幸运的是，您可以使用 Guice 的 Types.newParameterizedType 来创建完全指定的 TypeLiteral。

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public class MiddlewareModule<MessageType> extends AbstractModule {
private final Class<MessageType> _clazz;
private final List<Class<? extends PostprocessorMiddleware<MessageType>>> _postprocessors;
private final List<Class<? extends PreprocessorMiddleware<MessageType>>> _preprocessors;

public MiddlewareModule(
// Accept the message type in a way that survives erasure.
Class<MessageType> clazz,
List<Class<? extends PreprocessorMiddleware<MessageType>>> preprocessors,
List<Class<? extends PostprocessorMiddleware<MessageType>>> postprocessors
) {
_clazz = clazz;
_preprocessors = preprocessors;
_postprocessors = postprocessors;
}

@Override
protected void configure() {
// Use the Class to create your fully-specified TypeLiteral.
bindAllMiddleware(_preprocessors,
Types.newParameterizedType(PreprocessorMiddleware.class, _clazz));
bindAllMiddleware(_postprocessors,
Types.newParameterizedType(PostprocessorMiddleware.class, _clazz));
}

private <T extends Middleware> void bindAllMiddleware(List<Class<? extends T>> middleware, TypeLiteral< T > type) {
Multibinder< T > multibinder = Multibinder.newSetBinder(binder(), type);

middleware.forEach(middlewareType -> bindMiddleware(multibinder, middlewareType));
}

private <T extends Middleware> void bindMiddleware(Multibinder< T > binder, Class<? extends T> type) {
bind(type).in(Singleton.class); // Don't call binder() explicitly.
binder.addBinding().to(type);
}
}

请注意，这是未经测试的代码，因为我没有完整的 SSCCE；您可能需要调整类型参数以使 Guice 相信您在泛型中使用通配符是安全的。