android - 需要一个 Android 中的 HttpResponseCache 的例子

Question

您好，我正在尝试使用 Android 4 中引入的 HttpResponseCache。文档确实清楚地讨论了如何安装缓存，但我完全不知道如何缓存从网络下载的图像。之前我使用的是 DiskLruCache缓存它们。谁能给我指出一些使用了 HttpResponseCache 的工作代码示例。

编辑:- 谁能告诉我我做错了什么:-

MainActivity.java
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    final long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
    final File httpCacheDir = new File(getCacheDir(), "http");
    try {
        Class.forName("android.net.http.HttpResponseCache")
            .getMethod("install", File.class, long.class)
            .invoke(null, httpCacheDir, httpCacheSize);
        Log.v(TAG,"cache set up");
    } catch (Exception httpResponseCacheNotAvailable) {
        Log.v(TAG, "android.net.http.HttpResponseCache not available, probably because we're running on a pre-ICS version of Android. Using com.integralblue.httpresponsecache.HttpHttpResponseCache.");
        try{
            com.integralblue.httpresponsecache.HttpResponseCache.install(httpCacheDir, httpCacheSize);
        }catch(Exception e){
            Log.v(TAG, "Failed to set up com.integralblue.httpresponsecache.HttpResponseCache");
        }
    }
    TheMainListFrag gf=(TheMainListFrag) getSupportFragmentManager().findFragmentByTag("thelistfrags");
    if(gf==null){
        gf=TheMainListFrag.newInstance();
        FragmentTransaction ft=getSupportFragmentManager().beginTransaction();
        ft.replace(R.id.thelefty, gf,"thelistfrags");
        ft.commit();
    }
}

然后在 TheMainListFrag 的加载器中，我执行以下操作:-

public ArrayList<HashMap<String,String>> loadInBackground() {
    String datafromServer = null;
    ArrayList<HashMap<String,String>> al = new ArrayList<HashMap<String,String>>();
    try {
        String url = "someurl";
        HttpURLConnection urlConnection = (HttpURLConnection) new URL(url).openConnection();

        urlConnection.setRequestProperty("Accept", "application/json");
        InputStream is = new BufferedInputStream(urlConnection.getInputStream());
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = br.readLine()) != null) {
            sb.append(line);
        }
        datafromServer=sb.toString();
        Log.v("fromthread",datafromServer);
        // etc 
                    //etc

    } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (Exception e) {
        Log.v("fromthread", e.getClass() + "--" + e.getMessage());
    }

    return al;
}

当我连接到互联网时，它工作正常，并且在目录 http - 上面命名的缓存目录中，我也可以看到文件。但是当我没有连接到互联网时，数据拒绝加载。

当我从网络加载图像时，我看到名为 .tmp 的缓存文件，我认为根据 DiskLruCache 将其称为脏文件。

如果您希望我提供任何其他信息，请告诉我

Answer 1

来自 HttpResponseCache documentation 上的强制缓存响应部分:

Sometimes you'll want to show resources if they are available immediately, but not otherwise. This can be used so your application can show something while waiting for the latest data to be downloaded. To restrict a request to locally-cached resources, add the only-if-cached directive:

try {
    connection.addRequestProperty("Cache-Control", "only-if-cached");
    InputStream cached = connection.getInputStream();
    // the resource was cached! show it
} catch (FileNotFoundException e) {
    // the resource was not cached
}

This technique works even better in situations where a stale response is better than no response. To permit stale cached responses, use the max-stale directive with the maximum staleness in seconds:

int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
connection.addRequestProperty("Cache-Control", "max-stale=" + maxStale);