资源B关闭后自动关闭资源A

Question

激励示例：我有一个 HTTP 客户端，其唯一目的是生成单个

InputStream

。一旦

InputStream

关闭，HTTP 客户端也应该关闭。有没有办法将 HTTP 客户端的

close()

方法订阅到流的方法？

真正的问题是通用地这样做。我可以创建

InputStream

的子类覆盖

close()

并添加

httpClient.close()

，但也许明天我会面临同样的问题，但它不是 Http 客户端，而是文件句柄，或者我需要处置多个资源 B，当 A 关闭时 C、D，依此类推。能够将可关闭资源“订阅”到另一个资源将是理想的选择，但 API 似乎不支持这一点。

Answer 1

我认为你可以使用侦听器或观察者模式。这种模式允许一个资源（例如，InputStream）在关闭时通知订阅的资源，从而有效地创建订阅机制。

例如

public class SubscribableCloseable implements Closeable {
    private final Closeable mainResource;
    private final List<Closeable> subscribers = new ArrayList<>();

    public SubscribableCloseable(Closeable mainResource) {
        this.mainResource = mainResource;
    }

    public void subscribe(Closeable resource) {
        if (resource != null) {
            subscribers.add(resource);
        }
    }

    @Override
    public void close() throws IOException {
        IOException exception = null;

        try {
            // Close the main resource first
            mainResource.close();
        } catch (IOException e) {
            exception = e; // Capture any exception from the main resource close
        } finally {
            // Close all subscribed resources
            for (Closeable subscriber : subscribers) {
                try {
                    subscriber.close();
                } catch (IOException e) {
                    if (exception == null) {
                        exception = e; // Capture the first exception encountered
                    } else {
                        e.printStackTrace(); // Log subsequent exceptions
                    }
                }
            }
        }

        // If any exception occurred during closing, throw the first one encountered
        if (exception != null) {
            throw exception;
        }
    }
}

现在您可以将多个可关闭资源订阅到一个主可关闭资源，例如 InputStream。

public class HttpClientExample {
    public static void main(String[] args) throws IOException {
        URL url = new URL("http://example.com");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        InputStream inputStream = connection.getInputStream();
        SubscribableCloseable subscribableStream = new SubscribableCloseable(inputStream);

        // Subscribe the HttpURLConnection to the InputStream's close event
        subscribableStream.subscribe(() -> connection.disconnect());

        // Use the InputStream as needed
        // ... (read from the stream, process data, etc.)

        // Close the SubscribableCloseable, which triggers all subscribed closeables
        subscribableStream.close();
    }
}