建议添加 Guava ListenableFuture 相关执行器支持

[linzee1]

建议添加针对 Guava ListenableFuture 相关执行器接口支持，TtlExecutors 提供对 ListeningExecutorService，ListeningScheduledExecutorService 的支持。

原有实现若使用 TtlExecutors#getTtlExecutorService，返回结果没有实现 ListeningExecutorService 接口，只能在执行任务后手动强转为ListenableFuture。

使用装饰器模式时，可能不存在一个统一的方法（getTtlExecutor) 直接解决返回类型和委托类型的兼容问题，每个接口都需要写一个Wrapper实现。

以下是我自己的简单实现示例。

class Demo {
    public static ListeningExecutorService getTtlListeningExecutorService(ListeningExecutorService delegate) {
        return new ListeningExecutorServiceTtlWrapper(delegate, false);
    }

    @Value
    static class ListeningExecutorServiceTtlWrapper extends ForwardingListeningExecutorService implements TtlWrapper<ListeningExecutorService> {
        @NonNull
        ListeningExecutorService executor;
        boolean idempotent;

        // 避免耦合
        @Override
        protected ListeningExecutorService delegate() {
            return executor;
        }

        @Override
        public @NonNull ListeningExecutorService unwrap() {
            return executor;
        }

        @Override
        public <T> ListenableFuture<T> submit(Callable<T> task) {
            task = TtlCallable.get(task, false, idempotent);
            return super.submit(task);
        }

        // 略去其他
    }
}

[oldratlee]

+1

[linzee1]

又考虑了一下，写了一个适配器，针对包装执行 ListeningExecutorService 但是没有实现接口场景，比较通用。

public class ListenableHelper {
    /**
     * Adapts an ExecutorService to a {@link ListeningExecutorService}.
     * <p>This handles cases where the underlying ExecutorService can produce {@link ListenableFuture} instances
     * but does not directly implement the {@code ListeningExecutorService} interface. Such scenarios typically
     * occur when a {@code ListeningExecutorService} is wrapped by another decorator object (e.g., via the
     * decorator pattern), causing the original interface type to be obscured.
     */
    public static ListeningExecutorService adaptWrappedListeningExecutor(ExecutorService executorService) {
        if (executorService instanceof ListeningExecutorService) {
            return (ListeningExecutorService) executorService;
        }

        // optional check
        // if (executorService instanceof TtlWrapper) {
        //     TtlWrapper<?> ttlWrapper = (TtlWrapper<?>) executorService;
        //     Object inner = ttlWrapper.unwrap();
        //     if (inner instanceof ListeningExecutorService) {
        //         return new ListeningExecutorServiceAdapter(executorService);
        //     }
        // } else {
        //     throw new IllegalArgumentException("executorService must be a ListeningExecutorService in TtlWrapper");
        // }
        return new ListeningExecutorServiceAdapter(executorService);
    }
}

@AllArgsConstructor(access = AccessLevel.PACKAGE)
class ListeningExecutorServiceAdapter extends ForwardingExecutorService implements ListeningExecutorService {

    private final ExecutorService delegate;

    @Override
    protected ExecutorService delegate() {
        return delegate;
    }

    @Override
    public <T extends @Nullable Object> ListenableFuture<T> submit(Callable<T> task) {
        Future<T> result = super.submit(task);
        if (!(result instanceof ListenableFuture<T>)) {
            throw new IllegalStateException("executor service must return ListenableFuture");
        }
        return (ListenableFuture<T>) result;
    }

    @Override
    public ListenableFuture<?> submit(Runnable task) {
        Future<?> result = super.submit(task);
        if (!(result instanceof ListenableFuture<?>)) {
            throw new IllegalStateException("executor service must return ListenableFuture");
        }
        return (ListenableFuture<?>) result;
    }

    @Override
    public <T extends @Nullable Object> ListenableFuture<T> submit(Runnable task, T result) {
        Future<T> r = super.submit(task, result);
        if (!(r instanceof ListenableFuture<T>)) {
            throw new IllegalStateException("executor service must return ListenableFuture");
        }
        return (ListenableFuture<T>) r;
    }
}