Retrofit+OKHttp實現快取以及遇到的問題
阿新 • • 發佈：2019-02-04
原文連結：http://blog.csdn.net/Picasso_L/article/details/50579884#comments
簡介
retrofit本身並沒有快取。
如果想快取，它要麼必須讓retrofit之上的應用層知道你的域和如何快取事物，或它需要在retrofit之下HTTP client層知道HTTP的語義。
OkHttp是由Square釋出的一個HTTP client，它支援快取記憶體伺服器響應的語義。如果伺服器的響應具有Cache-Control頭，例如，它將被快取，以便隨後的請求可以從快取記憶體中的獲得之前的資源。
因此，裝置處於斷網情況下，retrofit與OKHttp配合可以實現快取。
但是大家必須注意一點，okhttp的快取設計和瀏覽器的一樣，是用來提升使用者體驗降低伺服器負荷的，比如：我們在有網的時候也會先呼叫快取，但是有個時間限制，例如1分鐘之內，有網和沒有網都是先讀快取，這個可以參考下面講解的第一種型別。
如果你想要做成那種離線可以快取，線上就獲取最新資料的功能，可以參考第二種型別
第一種型別（有網和沒有網都是先讀快取）
1、建立攔截器：
<code class="hljs vbscript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Interceptor interceptor = <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">new</span> Interceptor() {
@Override
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">public</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> intercept(Chain chain) throws IOException {
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Request</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span> = chain.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>();
LogCat.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"request="</span>+<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">Response</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span> = chain.proceed(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>);
LogCat.i(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"response="</span>+<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>);
<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">String</span> cacheControl = <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">request</span>.cacheControl().toString();
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (TextUtils.<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">isEmpty</span>(cacheControl)) {
cacheControl = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"public, max-age=60"</span>;
}
return <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">response</span>.newBuilder()
.header(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cache-Control"</span>, cacheControl)
.removeHeader(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pragma"</span>)
.build();
}
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>設定max-age為60s之後，這60s之內不管你有沒有網,都讀快取。（這也就說明了為什麼不能實現我上面說的功能）；max-stale設定為4周，意思是，網路未連線的情況下設定快取時間為4周。
2、設定client
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> //設定快取路徑
File httpCacheDirectory = new File(FileUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.getAvailableCacheDir</span>(), <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"responses"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
//設定快取 <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span>M
Cache cache = new Cache(httpCacheDirectory, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1024</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
//建立OkHttpClient，並新增攔截器和快取程式碼
OkHttpClient client = new OkHttpClient<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addNetworkInterceptor</span>(interceptor)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cache</span>(cache)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
//建立retrofit，把OkHttpClient物件寫入
Retrofit retrofit = new Retrofit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.baseUrl</span>(HttpUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.URL</span>_BASE)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.client</span>(client)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addConverterFactory</span>(GsonConverterFactory<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.create</span>())
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
service = retrofit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.create</span>(APIService<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.class</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>第二種型別（離線可以快取，線上就獲取最新資料）
這種方法和第一種方法的區別是在設定的攔截器上，這裡不能使用NetworkInterceptor，而是需要使用Interceptor，（不知道為什麼用NetworkInterceptor就不行）
先講一下步驟：
* 1、 首先，給OkHttp設定攔截器
* 2、然後，在攔截器內做Request攔截操作，在每個請求發出前，判斷一下網路狀況，如果沒問題繼續訪問，如果有問題，則設定從本地快取中讀取
* 3、接下來是設定Response，先判斷網路，網路好的時候，移除header後新增cache失效時間為0小時，網路未連線的情況下設定快取時間為4周
程式碼：
1、給OkHttp設定攔截器（用Interceptor）
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> OkHttpClient client = new OkHttpClient<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addInterceptor</span>(interceptor)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cache</span>(cache)<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
Retrofit retrofit = new Retrofit<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.Builder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.baseUrl</span>(HttpUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.URL</span>_BASE)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.client</span>(client)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.addConverterFactory</span>(GsonConverterFactory<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.create</span>())
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>
2、Request攔截操作
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> Request request = chain<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.request</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
if (!StringsUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isNetworkReachable</span>(App<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.app</span>)) {
request = request<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newBuilder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.cacheControl</span>(CacheControl<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.FORCE</span>_CACHE)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
LogCat<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"no network"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li></ul>
3、設定Response
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">Response response = chain<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.proceed</span>(request)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
if (StringsUtil<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.isNetworkReachable</span>(App<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.app</span>)) {
int maxAge = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">60</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // 有網路時 設定快取超時時間0個小時</span>
LogCat<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"has network maxAge="</span>+maxAge)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newBuilder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cache-Control"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"public, max-age="</span> + maxAge)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.removeHeader</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pragma"</span>)// 清除頭資訊，因為伺服器如果不支援，會返回一些干擾資訊，不清除下面無法生效
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
} else {
LogCat<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"network error"</span>)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
int maxStale = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">60</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">60</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">24</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">28</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">; // 無網路時，設定超時為4周</span>
LogCat<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"has maxStale="</span>+maxStale)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
response<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.newBuilder</span>()
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.header</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Cache-Control"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"public, only-if-cached, max-stale="</span> + maxStale)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.removeHeader</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Pragma"</span>)
<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.build</span>()<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
LogCat<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.i</span>(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"response build maxStale="</span>+maxStale)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
}
return response<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>
這樣就ok了。
檢視快取檔案
下面我們講一下快取的檔案，發現快取檔案全是以url的md5加密欄位為檔名，每一個response分兩個檔案儲存，以.0和.1結尾的檔案區分。 進去看裡面的內容如下： .0的檔案裡面是header：
執行程式，在Android/data/xxxxxx(包名)/responses下會發現很多快取檔案，這些快取檔案全是以url的md5加密欄位為檔名，每一個response分兩個檔案儲存，以.0和.1結尾的檔案區分。舉個例子：
2d58c369c11640eafe880241d31ad7a2.0
2d58c369c11640eafe880241d31ad7a2.1
.0的檔案裡面是header
而.1檔案裡面是返回的具體內容，即json資料。 
由此可見，這裡的快取機制也是一開始先把json快取進檔案，沒有網路的時候再讀取json進行解析。
但是還有一個journal.檔案，這個裡面是什麼呢。
可以看到裡面儲存的是每一條reponse記錄狀態。包括讀取，刪除，寫入等動作。