Issue 4485 - Clear cache directory

src/org/adblockplus/sbrowser/contentblocker/engine/Engine.java

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 238 matching lines @@
     this.lock();
     try
     {
       Log.d(TAG, "Writing filters...");
       final File filterFile = this.subscriptions.createAndWriteFile();
 
       final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this.serviceContext);
       final String key = this.serviceContext.getString(R.string.key_cached_filter_path);
       prefs.edit().putString(key, filterFile.getAbsolutePath()).commit();
 
+      Log.d(TAG, "Cleaning up cache...");
+      final File dummyFile = getDummyFilterFile(this.serviceContext);
+      for (final File file : getFilterCacheDir(this.serviceContext).listFiles())

[anton, 2016/09/30 06:17:15]

listFiles() can return `null` is getFilterCacheDir() does not exist. If you're
sure the directory exists, then it's ok, Otherwise check for null.
BTW, if something like that is used anywhere else i'd prefer to move it to
`FileUtils` helper class or smth like that. Not too important though

[diegocarloslima, 2016/09/30 14:35:47]

The directory should exists in order for the previous line to succeed: 'final
File filterFile = this.subscriptions.createAndWriteFile()', but it won't hurt to
add a null check here since the cache cleaning is sort of an optional step, so
it shouldn't ever raise an Exception.

About the FileUtils: There are some other IO logic across the project that can
be moved to a helper class too, but that refactoring should be done in a
separate issue. 

+      {
+        if (!file.equals(dummyFile) && !file.equals(filterFile))
+        {
+          Log.d(TAG, "Deleting file:" + file);
+          file.delete();
+        }
+      }
     }
     catch (IOException e)
     {
       Log.e(TAG, "Failed to write filters", e);
     }
     finally
     {
       this.unlock();
     }
   }
@@ skipping 443 matching lines @@
       Log.d(TAG, headers.toString());
       this.downloader.enqueueDownload(this.createDownloadURL(sub), sub.getId(), headers);
     }
   }
 
   public void connectivityChanged()
   {
     this.downloader.connectivityChanged();
   }
 }