Question

我在Android中从Web服务器缓存http（s）响应时遇到问题，文档很差，所以我在这里寻求帮助。这是我的代码：

    String encodedString = String.format("jsonData=%s", URLEncoder.encode(json, "UTF-8"));

    URL urlConn = new URL(url+"?"+encodedString);

    HttpURLConnection cachedUrlConnection = (HttpURLConnection) urlConn.openConnection();
    cachedUrlConnection.setUseCaches(true);
    cachedUrlConnection.setDoInput(true);
    cachedUrlConnection.setDoOutput(true);
    cachedUrlConnection.setRequestProperty("charset", "utf-8");
    cachedUrlConnection.setRequestMethod("GET");

    cachedUrlConnection.addRequestProperty("Cache-Control", "only-if-cached");


    InputStream is = null;
    try {
        is = cachedUrlConnection.getInputStream();

        Log.i("_INFO","------CACHE FOUNDED");

    } catch (FileNotFoundException e){
        e.printStackTrace();

        HttpURLConnection nonCachedUrlConnection = (HttpURLConnection) urlConn.openConnection();
        nonCachedUrlConnection.setUseCaches(true);
        nonCachedUrlConnection.setDoInput(true);
        nonCachedUrlConnection.setDoOutput(true);
        nonCachedUrlConnection.setRequestProperty("charset", "utf-8");
        nonCachedUrlConnection.setRequestMethod("GET");
        nonCachedUrlConnection.addRequestProperty("Cache-Control", "max-stale=" + (60 * 60 * 24));

        Log.i("_INFO","-------CACHE NOT FOUNDED");

        is = nonCachedUrlConnection.getInputStream();
    }

另外，我已经在Application onCreate方法上安装了缓存，如下所示：

try {
        long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
        File httpCacheDir = new File(getExternalCacheDir(), "http");
        Class.forName("android.net.http.HttpResponseCache")
                .getMethod("install", File.class, long.class)
                .invoke(null, httpCacheDir, httpCacheSize);

        Log.i("_INFO", "HttpResponseCache enabled");

    } catch (Exception httpResponseCacheNotAvailable) {
        Log.d("_INFO", "HTTP response cache is unavailable.");
    }

如果我打印缓存大小，在应用程序重新启动后，它会正确打印2 mb 的缓存大小（因此它可以正确缓存）。我在所有HTTP调用之后刷新缓存，如下所示：

HttpResponseCache cache = HttpResponseCache.getInstalled();
        if(cache != null) {
            Log.i("_INFO", "CACHED FLUSHED WITH " + cache.size());
            cache.flush();
        }

所以，基本上，缓存过程效果很好，但是我在getInputStream时无法获取缓存的响应。我的logcat始终打印＆＃34; CACHE NOT FOUNDED＆＃34;。

Answer 1

过了一段时间我最终得到了解决方案，似乎我的HTTP调用上有太多参数，或者可能是错误的。

仅限：

cachedUrlConnection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);

这一个，缓存工作迷人。

Android HttpResponseCache无法正常工作--FileNotFoundException

1 个答案: