1

我在 Android 中缓存来自 Web 服务器的 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，缓存过程工作得很好，但是当我 getInputStream 时我无法获取缓存的响应。我的 logcat 总是打印“CACHE NOT FOUNDED”。

4

1 回答 1

2

过了一会儿，我最终得到了解决方案，似乎我的 HTTP 调用中的参数太多，或者可能是错误的。

只有：

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

这一个，缓存的工作很迷人。

于 2014-11-04T09:05:21.793 回答