文件缓存法的具体实现

针对配置文件的缓存，我新建了一个类ConfigCache:

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import java.io.File; import java.io.IOException;   import android.util.Log;   import com.tianxia.app.floworld.AppApplication; import com.tianxia.app.floworld.utils.FileUtils; import com.tianxia.app.floworld.utils.NetworkUtils;   public class ConfigCache {     private static final String TAG = ConfigCache.class.getName();       public static final int CONFIG_CACHE_MOBILE_TIMEOUT  = 3600000;  //1 hour     public static final int CONFIG_CACHE_WIFI_TIMEOUT    = 300000;   //5 minute       public static String getUrlCache(String url) {         if (url == null) {             return null;         }           String result = null;         File file = new File(AppApplication.mSdcardDataDir + "/" + getCacheDecodeString(url));         if (file.exists() && file.isFile()) {             long expiredTime = System.currentTimeMillis() - file.lastModified();             Log.d(TAG, file.getAbsolutePath() + " expiredTime:" + expiredTime/60000 + "min");             //1. in case the system time is incorrect (the time is turn back long ago)             //2. when the network is invalid, you can only read the cache             if (AppApplication.mNetWorkState != NetworkUtils.NETWORN_NONE && expiredTime < 0) {                 return null;             }             if(AppApplication.mNetWorkState == NetworkUtils.NETWORN_WIFI                    && expiredTime > CONFIG_CACHE_WIFI_TIMEOUT) {                 return null;             } else if (AppApplication.mNetWorkState == NetworkUtils.NETWORN_MOBILE                    && expiredTime > CONFIG_CACHE_MOBILE_TIMEOUT) {                 return null;             }             try {                 result = FileUtils.readTextFile(file);             } catch (IOException e) {                 e.printStackTrace();             }         }         return result;     }       public static void setUrlCache(String data, String url) {         File file = new File(AppApplication.mSdcardDataDir + "/" + getCacheDecodeString(url));         try {             //创建缓存数据到磁盘，就是创建文件             FileUtils.writeTextFile(file, data);         } catch (IOException e) {             Log.d(TAG, "write " + file.getAbsolutePath() + " data failed!");             e.printStackTrace();         }     }       public static String getCacheDecodeString(String url) {         //1. 处理特殊字符         //2. 去除后缀名带来的文件浏览器的视图凌乱(特别是图片更需要如此类似处理，否则有的手机打开图库，全是我们的缓存图片)         if (url != null) {             return url.replaceAll("[.:/,%?&=]", "+").replaceAll("[+]+", "+");         }         return null;     } }

      从实现上我们全面考虑了几个细节，注释已经说明，不再赘述。
      然后我们调用方法如下：

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void getConfig(){         //首先尝试读取缓存         String cacheConfigString = ConfigCache.getUrlCache(CONFIG_URL);         //根据结果判定是读取缓存，还是重新读取         if (cacheConfigString != null) {             showConfig(cacheConfigString);         } else {             //如果缓存结果是空，说明需要重新加载             //缓存为空的原因可能是1.无缓存;2. 缓存过期;3.读取缓存出错             AsyncHttpClient client = new AsyncHttpClient();             client.get(CONFIG_URL, new AsyncHttpResponseHandler(){                   @Override                 public void onSuccess(String result){                     //成功下载，则保存到本地作为后面缓存文件                     ConfigCache.setUrlCache(result,  CONFIG_URL);                     //后面可以是UI更新，仅供参考                     showConfig(result);                 }                   @Override                 public void onFailure(Throwable arg0) {                     //根据失败原因，考虑是显示加载失败，还是再读取缓存                 }               });         }     }

　　这样配置文件既能有效缓存，又能及时更新了，同时支持离线浏览。