android - 使用 OkHttp 进行缓存(无需改造)

Question

在我的应用程序 onCreate 中，我正在创建一个 10MB 的缓存:

try
{
    File httpCacheDir = new File(getApplicationContext().getCacheDir(), Constants.AppName);
    long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
    HttpResponseCache.install(httpCacheDir, httpCacheSize);
}
catch (IOException ex)
{
    Log.i(Constants.AppName, "HTTP response cache installation failed: " + ex);
}

我对资源的调用:

OkHttpClient client = new OkHttpClient();
client.setResponseCache(HttpResponseCache.getInstalled());

HttpURLConnection connection = client.open(url);
connection.addRequestProperty("Cache-Control", "max-age=60");
InputStream inputStream = connection.getInputStream();

我将在 10 秒内初始化此调用两次，OkHttp-Response-Source header 始终为 NETWORK 200。

for (Map.Entry<String, List<String>> k : connection.getHeaderFields().entrySet())
{
    for (String v : k.getValue())
    {
        Log.d(Constants.AppName, k.getKey() + ": " + v);
    }
}

我在这里错过了什么？

Answer 1

OkHttp 实现HTTP 1.1 RFC for HTTP cache .这意味着，对于您尝试访问的任何 URL，响应至少需要返回 Cache-Control header :

The basic cache mechanisms in HTTP/1.1 (server-specified expiration times and validators) are implicit directives to caches. In some cases, a server or client might need to provide explicit directives to the HTTP caches. We use the Cache-Control header for this purpose.

The Cache-Control header allows a client or server to transmit a variety of directives in either requests or responses. These directives typically override the default caching algorithms. As a general rule, if there is any apparent conflict between header values, the most restrictive interpretation is applied (that is, the one that is most likely to preserve semantic transparency). However,

in some cases, cache-control directives are explicitly specified as weakening the approximation of semantic transparency (for example, "max-stale" or "public").

The cache-control directives are described in detail in section 14.9.