blocks|key|187178|text|查看此答案-+Set+expiration+policy+for+cache+using+Google's+Volley|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|187179|这意味着Volley只根据"+cache+-Control“和"Expires”、"maxAge“来决定是否缓存响应。|187180|您可以做的是更改此方法com.android.volley.toolbox.HttpHeaderParser.parseCacheHeaders(NetworkResponse+response)并忽略这些头文件，将entry.softTtl和entry.ttl字段设置为适合您的任何值，并在请求类中使用您的方法。下面是一个示例：|style|CODE|187181|/**
+*+Extracts+a+{@link+Cache.Entry}+from+a+{@link+NetworkResponse}.
+*+Cache-control+headers+are+ignored.+SoftTtl+==+3+mins,+ttl+==+24+hours.
+*+@param+response+The+network+response+to+parse+headers+from
+*+@return+a+cache+entry+for+the+given+response,+or+null+if+the+response+is+not+cacheable.
+*/
public+static+Cache.Entry+parseIgnoreCacheHeaders(NetworkResponse+response)+{
++++long+now+=+System.currentTimeMillis();

++++Map<String,+String>+headers+=+response.headers;
++++long+serverDate+=+0;
++++String+serverEtag+=+null;
++++String+headerValue;

++++headerValue+=+headers.get("Date");
++++if+(headerValue+!=+null)+{
++++++++serverDate+=+HttpHeaderParser.parseDateAsEpoch(headerValue);
++++}

++++serverEtag+=+headers.get("ETag");

++++final+long+cacheHitButRefreshed+=+3+*+60+*+1000;+//+in+3+minutes+cache+will+be+hit,+but+also+refreshed+on+background
++++final+long+cacheExpired+=+24+*+60+*+60+*+1000;+//+in+24+hours+this+cache+entry+expires+completely
++++final+long+softExpire+=+now+%2B+cacheHitButRefreshed;
++++final+long+ttl+=+now+%2B+cacheExpired;

++++Cache.Entry+entry+=+new+Cache.Entry();
++++entry.data+=+response.data;
++++entry.etag+=+serverEtag;
++++entry.softTtl+=+softExpire;
++++entry.ttl+=+ttl;
++++entry.serverDate+=+serverDate;
++++entry.responseHeaders+=+headers;

++++return+entry;
}|code-block|syntax|javascript|187182|在请求类中使用此方法，如下所示：|187183|public+class+MyRequest+extends+com.android.volley.Request<MyResponse>+{

++++...

++++@Override
++++protected+Response<MyResponse>+parseNetworkResponse(NetworkResponse+response)+{
++++++++String+jsonString+=+new+String(response.data);
++++++++MyResponse+MyResponse+=+gson.fromJson(jsonString,+MyResponse.class);
++++++++return+Response.success(MyResponse,+HttpHeaderParser.parseIgnoreCacheHeaders(response));
++++}

}|187184|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/16783177/set-expiration-policy-for-cache-using-googles-volley^0|7|1H|0|0|0|B|2F|30|D|3E|9|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|6|7|15|8|@$A|16|B|17|H|I]|$A|18|B|19|H|I]|$A|1A|B|1B|H|I]]|9|@]|C|$]]|$1|J|3|K|5|L|7|1C|8|@]|9|@]|C|$M|N]]|$1|O|3|P|5|6|7|1D|8|@]|9|@]|C|$]]|$1|Q|3|R|5|L|7|1E|8|@]|9|@]|C|$M|N]]|$1|S|3|-4|5|6|7|1F|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

See this answer - <a href="https://stackoverflow.com/questions/16783177/set-expiration-policy-for-cache-using-googles-volley">Set expiration policy for cache using Google&#39;s Volley</a>

This means Volley decides whether to cache response or not based only on headers "Cache-Control" and then "Expires", "maxAge".

What you could do is change this method
<code>com.android.volley.toolbox.HttpHeaderParser.parseCacheHeaders(NetworkResponse response)</code>
and ignore these headers, set <code>entry.softTtl</code> and <code>entry.ttl</code> fields to whatever value works for you and use your method in your request class. Here is an example:

<pre><code>/**
 * Extracts a {@link Cache.Entry} from a {@link NetworkResponse}.
 * Cache-control headers are ignored. SoftTtl == 3 mins, ttl == 24 hours.
 * @param response The network response to parse headers from
 * @return a cache entry for the given response, or null if the response is not cacheable.
 */
public static Cache.Entry parseIgnoreCacheHeaders(NetworkResponse response) {
 long now = System.currentTimeMillis();

 Map&lt;String, String&gt; headers = response.headers;
 long serverDate = 0;
 String serverEtag = null;
 String headerValue;

 headerValue = headers.get("Date");
 if (headerValue != null) {
 serverDate = HttpHeaderParser.parseDateAsEpoch(headerValue);
 }

 serverEtag = headers.get("ETag");

 final long cacheHitButRefreshed = 3 * 60 * 1000; // in 3 minutes cache will be hit, but also refreshed on background
 final long cacheExpired = 24 * 60 * 60 * 1000; // in 24 hours this cache entry expires completely
 final long softExpire = now + cacheHitButRefreshed;
 final long ttl = now + cacheExpired;

 Cache.Entry entry = new Cache.Entry();
 entry.data = response.data;
 entry.etag = serverEtag;
 entry.softTtl = softExpire;
 entry.ttl = ttl;
 entry.serverDate = serverDate;
 entry.responseHeaders = headers;

 return entry;
}
</code></pre>

Use this method in your Request class like this:

<pre><code>public class MyRequest extends com.android.volley.Request&lt;MyResponse&gt; {

 ...

 @Override
 protected Response&lt;MyResponse&gt; parseNetworkResponse(NetworkResponse response) {
 String jsonString = new String(response.data);
 MyResponse MyResponse = gson.fromJson(jsonString, MyResponse.class);
 return Response.success(MyResponse, HttpHeaderParser.parseIgnoreCacheHeaders(response));
 }

}
</code></pre>

blocks|key|187753|text|oleksandr_yefremov提供了很棒的代码，可以帮助你处理安卓截击的缓存策略，特别是当REST+API有不正确的cache+-+control头部时，或者你只是想更多地控制自己的应用缓存策略。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|187754|关键是HttpHeaderParser.parseCacheHeaders(NetworkResponse+response))。如果你想拥有自己的缓存策略。将其替换为对应类中的parseIgnoreCacheHeaders(NetworkResponse+response)。|offset|length|style|CODE|BOLD|187755|如果您的类扩展了JsonObjectRequest，请转到JsonObjectRequest并查找|187756|@Override
protected+Response<JSONObject>+parseNetworkResponse(NetworkResponse+response)+{
++++try+{
++++++++++++String+jsonString+=new+String(response.data,+HttpHeaderParser.parseCharset(response.headers));
++++++++++++return+Response.success(new+JSONObject(jsonString),HttpHeaderParser.parseCacheHeaders(response));
++++++++}catch+(UnsupportedEncodingException+e)+{
++++++++++++return+Response.error(new+ParseError(e));
++++++++}catch+(JSONException+je)+{
++++++++++++return+Response.error(new+ParseError(je));
++++++++}
}|code-block|syntax|javascript|187757|并用HttpHeaderParser.parseIgnoreCacheHeaders替换HttpHeaderParser.parseCacheHeaders(response)|187758|entityMap^0|0|3|1P|2H|1D|2C|3|0|0|0|2|14|18|18|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|U|8|@$D|V|E|W|F|G]|$D|X|E|Y|F|G]|$D|Z|E|10|F|H]]|9|@]|A|$]]|$1|I|3|J|5|6|7|11|8|@]|9|@]|A|$]]|$1|K|3|L|5|M|7|12|8|@]|9|@]|A|$N|O]]|$1|P|3|Q|5|6|7|13|8|@$D|14|E|15|F|G]|$D|16|E|17|F|G]]|9|@]|A|$]]|$1|R|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|S|$]]

oleksandr_yefremov provides great codes that can help you when you dealing with cache strategy of Android Volley, especially when the REST API has improper "Cache-Control" headers or you just want more control on your own app cache strategy.

The key is <code>HttpHeaderParser.parseCacheHeaders(NetworkResponse response))</code>. If you want to have your own cache strategy. Replace it with <code>parseIgnoreCacheHeaders(NetworkResponse response)</code> in corresponding class. 

If your class extends JsonObjectRequest, go to JsonObjectRequest and find 

<pre><code>@Override
protected Response&lt;JSONObject&gt; parseNetworkResponse(NetworkResponse response) {
 try {
 String jsonString =new String(response.data, HttpHeaderParser.parseCharset(response.headers));
 return Response.success(new JSONObject(jsonString),HttpHeaderParser.parseCacheHeaders(response));
 }catch (UnsupportedEncodingException e) {
 return Response.error(new ParseError(e));
 }catch (JSONException je) {
 return Response.error(new ParseError(je));
 }
}
</code></pre>

and replace <code>HttpHeaderParser.parseCacheHeaders(response)</code> with <code>HttpHeaderParser.parseIgnoreCacheHeaders</code>

blocks|key|189913|text|%2B1也适用于oleksandr_yefremov和skyfishjy，并在这里提供了一个具体的、可重用的类，适用于json或其他基于字符串的API：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|189914|public+class+CachingStringRequest+extends+StringRequest+{
++++public+CachingStringRequest(int+method,+String+url,+Response.Listener<String>+listener,+Response.ErrorListener+errorListener)+{
++++++++super(method,+url,+listener,+errorListener);
++++}

++++public+CachingStringRequest(String+url,+Response.Listener<String>+listener,+Response.ErrorListener+errorListener)+{
++++++++super(url,+listener,+errorListener);
++++}

++++@Override
++++protected+Response<String>+parseNetworkResponse(NetworkResponse+response)+{
++++++++String+parsed;
++++++++try+{
++++++++++++parsed+=+new+String(response.data,+HttpHeaderParser.parseCharset(response.headers));
++++++++}+catch+(UnsupportedEncodingException+e)+{
++++++++++++parsed+=+new+String(response.data);
++++++++}
++++++++return+Response.success(parsed,+parseIgnoreCacheHeaders(response));
++++}
}|code-block|syntax|javascript|189915|其中函数parseIgnoreCacheHeaders()来自上面的oleksandr_yefremov答案。在生成的json可以缓存3分钟(实时)和24小时(过期但仍然可用)的任何地方使用CachingStringRequest类。示例请求：|189916|CachingStringRequest+stringRequest+=+new+CachingStringRequest(MY_API_URL,+callback);|189917|在回调对象的onResponse()函数中，解析json。设置您想要的任何缓存限制--您可以对每个请求进行参数化，以添加自定义过期。|189918|为了好玩，可以在一个简单的应用程序中尝试一下，该应用程序下载json并呈现下载的信息。用第一次成功的下载填充缓存后，在缓存处于活动状态时更改方向时，请观察快速渲染(如果实时缓存命中，则不会发生下载)。现在关闭应用程序，等待3分钟，等待缓存命中过期(但不是24小时，将其从缓存中删除)，启用飞行模式，然后重新启动应用程序。将发生截击错误回调，并且将从缓存的数据中执行“成功的”onResponse()回调，从而允许您的应用程序既呈现内容，又知道/警告它来自过期的缓存。|189919|这种缓存的一种用途是避免Loaders和其他处理方向变化的方法。如果请求通过Volley+singleton，并且结果被缓存，则通过方向更改发生的刷新将从缓存中快速呈现，由Volley自动呈现，而无需Loader。|189920|当然，这并不能满足所有需求。YMMV|189921|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

+1 for oleksandr_yefremov and skyfishjy also, and offering here a concrete, reusable class suitable for json or other string-based APIs:

<pre><code>public class CachingStringRequest extends StringRequest {
 public CachingStringRequest(int method, String url, Response.Listener&lt;String&gt; listener, Response.ErrorListener errorListener) {
 super(method, url, listener, errorListener);
 }

 public CachingStringRequest(String url, Response.Listener&lt;String&gt; listener, Response.ErrorListener errorListener) {
 super(url, listener, errorListener);
 }

 @Override
 protected Response&lt;String&gt; parseNetworkResponse(NetworkResponse response) {
 String parsed;
 try {
 parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
 } catch (UnsupportedEncodingException e) {
 parsed = new String(response.data);
 }
 return Response.success(parsed, parseIgnoreCacheHeaders(response));
 }
}
</code></pre>

where the function parseIgnoreCacheHeaders() comes from the oleksandr_yefremov answer above. Use the CachingStringRequest class anywhere that the resulting json is ok to cache for 3 minutes (live) and 24 hours (expired but still available). A sample request:

<pre><code>CachingStringRequest stringRequest = new CachingStringRequest(MY_API_URL, callback);
</code></pre>

and within the callback object's onResponse() function, parse the json. Set whatever caching limits you want--you could parameterize to add custom expiration per request.

For fun, try this in a simple app that downloads json and renders the downloaded info. Having filled the cache with the first successful download, watch the speedy rendering as you change orientations while cache is live (no download occurs given a live cache hit). Now kill the app, wait 3 minutes for that cache hit to expire (but not 24 hours for it to be removed from cache), enable airplane mode, and restart the app. The Volley error callback will occur, AND the "successful" onResponse() callback will occur from cached data, allowing your app to both render content and also know/warn that it came from expired cache. 

One use of this kind of caching would be to obviate Loaders and other means of dealing with orientation change. If a request goes through a Volley singleton, and results are cached, refreshes that happen via orientation change are rendered quickly from cache, automatically by Volley, without the Loader. 

Of course, this doesn't fit all requirements. YMMV

blocks|key|3018353|text|我可以通过扩展StringRequest并用CachingStringRequest替换我想要强制缓存的请求来强制Volley缓存所有响应。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|3018354|在被覆盖的方法parseNetworkResponse中，我删除了Cache-Control标头。这样Volley就会将响应持久化到它的内置缓存中。|3018355|public+class+CachingStringRequest+extends+StringRequest+{
++++private+static+final+String+CACHE_CONTROL+=+"Cache-Control";

++++public+CachingStringRequest(int+method,
++++++++++++++++++++++++++++++++String+url,
++++++++++++++++++++++++++++++++Response.Listener<String>+listener,
++++++++++++++++++++++++++++++++Response.ErrorListener+errorListener)+{
++++++++super(method,+url,+listener,+errorListener);
++++}

++++@Override
++++protected+Response<String>+parseNetworkResponse(NetworkResponse+response)+{
++++++++//+I+do+this+to+ignore+"no-cache"+headers
++++++++//+and+use+built-in+cache+from+Volley.
++++++++if+(response.headers.containsKey(CACHE_CONTROL))+{
++++++++++++response.headers.remove(CACHE_CONTROL);
++++++++}

++++++++return+super.parseNetworkResponse(response);
++++}
}|code-block|syntax|javascript|3018356|entityMap^0|7|D|M|K|0|7|K|X|D|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]|$9|W|A|X|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|Y|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|N|$]]

I was able to force Volley to cache all responses by extending <code>StringRequest</code> and replacing request I want to forcibly cache with <code>CachingStringRequest</code>.

In overridden method <code>parseNetworkResponse</code> I remove <code>Cache-Control</code> headers. This way Volley is persisting the response in it's built-in cache.

<pre><code>public class CachingStringRequest extends StringRequest {
 private static final String CACHE_CONTROL = "Cache-Control";

 public CachingStringRequest(int method,
 String url,
 Response.Listener&lt;String&gt; listener,
 Response.ErrorListener errorListener) {
 super(method, url, listener, errorListener);
 }

 @Override
 protected Response&lt;String&gt; parseNetworkResponse(NetworkResponse response) {
 // I do this to ignore "no-cache" headers
 // and use built-in cache from Volley.
 if (response.headers.containsKey(CACHE_CONTROL)) {
 response.headers.remove(CACHE_CONTROL);
 }

 return super.parseNetworkResponse(response);
 }
}
</code></pre>

<pre><code>public class CustomRequest extends JsonObjectRequest {

 public CustomRequest(String url, JSONObject params,
 Listener&lt;JSONObject&gt; listener, ErrorListener errorListener)
 throws JSONException {
 super(Method.POST,url, params, listener,
 errorListener);
 this.setShouldCache(Boolean.TRUE);
 }
}
</code></pre>

I was hoping that this piece of code would be enough for me to get implicit caching of responses. I'm not sure if it works or not, because i was under the assumption when a request is sent:

<ol>
<li>it would hit the cache first and send that to onresponse</li>
<li>then when the results come through from the remote server it would provide it to the onresponse </li>
</ol>

Update:

I figured how to manually retrieve the cache and reconstruct it into a JSONObject and send it through OnResponse function but that doesn't seem to efficient considering there is implicit caching. JsonObjectRequest class should return JSONObject as the cached entry instead of raw response data.

But i'm still interested to know if i'm making some mistake.

The ambiguity is solely due to the lack of documentation, so i apologize if i'm missing something quite obvious.

Android Volley + JSONObjectRequest Caching

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