Question

我有以下代码块：

try {
    URL url = new URL("http://site-to-test.com/nonexistingpage.html");

    HttpURLConnection urlc = (HttpURLConnection) url.openConnection();
    urlc.setRequestProperty("User-Agent", CoreProtocolPNames.USER_AGENT);
    urlc.setRequestProperty("Connection", "close");
    urlc.setConnectTimeout(500); // timeout is in milliseconds
    urlc.connect();

    if (urlc.getResponseCode() == 404) {
        // Server was reachable
        Log.i(TAG, "Server is reachable");
    }

} catch (MalformedURLException mue) {
    Log.e(TAG, "MalformedURLException: " + mue.getMessage());
} catch (IOException e) {
    Log.e(TAG, "IOException: " + e.getMessage());
}

当无法通过当前网络访问site-to-test域时，此代码会在收到IOException之前阻塞大约30-40秒。我特意将超时值设置为500毫秒。我在这里错过了什么？无论网络状态和网站的可用性如何，上述块是否应该在半秒内终止？

Answer 1

似乎是Java URLConnection provides no fail-safe timeout on reads

正如文章所解释的那样，解决方案是使用单独的Thread进行计时，并在完成计时器线程后手动断开HttpURLConnection。

Answer 2

经过深入调查和大量的跟踪后，我发现实现AsyncTask（或Service，用于执行后台工作的对象）的计时器远离HTTP连接类的最佳方法，就像有时断开HTTP连接一样连接，这不会中断Web调用，我实现了这个类，当您需要对HTTP连接进行超时检查时使用

public abstract class AsyncTaskWithTimer<Params, Progress, Result> extends
    AsyncTask<Params, Progress, Result> {

    private static final int HTTP_REQUEST_TIMEOUT = 30000;

    @Override
    protected Result doInBackground(Params... params) {
        createTimeoutListener();
        return doInBackgroundImpl(params);
    }

    private void createTimeoutListener() {
        Thread timeout = new Thread() {
            public void run() {
                Looper.prepare();

                final Handler handler = new Handler();
                handler.postDelayed(new Runnable() {
                    @Override
                    public void run() {

                        if (AsyncTaskWithTimer.this != null
                                && AsyncTaskWithTimer.this.getStatus() != Status.FINISHED)
                            AsyncTaskWithTimer.this.cancel(true);
                        handler.removeCallbacks(this);
                        Looper.myLooper().quit();
                    }
                }, HTTP_REQUEST_TIMEOUT);

                Looper.loop();
            }
        };
        timeout.start();
    }

    abstract protected Result doInBackgroundImpl(Params... params);
}

此示例

public class AsyncTaskWithTimerSample extends AsyncTaskWithTimer<Void, Void, Void> {

    @Override
    protected void onCancelled(Void void) {
        Log.d(TAG, "Async Task onCancelled With Result");
        super.onCancelled(result);
    }

    @Override
    protected void onCancelled() {
        Log.d(TAG, "Async Task onCancelled");
        super.onCancelled();
    }

    @Override
    protected Void doInBackgroundImpl(Void... params) {
        // Do background work
        return null;
    };
 }

为什么android HttpURLConnection不遵守超时值？

2 个答案: