java - Guice - 相同返回类型的多个提供者方法

Question

在我的模块中:

@Provides
@Singleton
public ExecutorService provideExecutorService(){
    return new ExecutorService(config);
}

在我的课上:

@Inject
private ExecutorService executorService;

现在，我需要两个具有不同配置的 ExecutorService 实例:

@Provides
@Singleton
public ExecutorService provideExecutorServiceA(){
    return new ExecutorService(configA);
}

@Provides
@Singleton
public ExecutorService provideExecutorServiceB(){
    return new ExecutorService(configB);
}

如果我想为类中使用 configB 创建的 ExecutorService 注入(inject) ExecutorService，我该怎么做？

Answer 1

您可以使用 binding annotations :

@Provides
@Singleton
@Priority(Priority.Level.HIGH)
public static ReportingDal createHighPriorityReportingDal(DataSource dataSource,
                                                          DatabaseType databaseType,
                                                          ReportingQueryGenerator queryGenerator)
{
    return new ReportingDalImpl(dataSource, databaseType, Queue.DEFAULT, queryGenerator);
}

@Provides
@Singleton
@Priority(Priority.Level.LOW)
public static ReportingDal createLowPriorityReportingDal(DataSource dataSource,
                                                         DatabaseType databaseType,
                                                         ReportingQueryGenerator queryGenerator)
{
    return new ReportingDalImpl(dataSource, databaseType, Queue.MAINTENANCE, queryGenerator);
}

@Priority 注释看起来像这样:

@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })
@BindingAnnotation
public @interface Priority
{
    Level value();

    public enum Level
    {
        LOW,
        HIGH
    }
}

请注意，如果您不想实现自定义注释，您可以使用 @Named annotation那是内置的 Guice。然后你可以像这样在你的类中使用它:

@Inject
public ReportingJob(@Priority(Priority.Level.LOW) ReportingDal dal)
{
    this.dal = dal;
}

编辑

或者，如果您通过私有(private)字段注入(inject):

@Inject
@Priority(Priority.Level.LOW)
private ReportingDal dal;