Change to io executor, remove delete temp file and nit changes

Author: wangmengyan95

Parse/src/main/java/com/parse/ParseFileController.java

@@ -60,7 +60,7 @@ public File getCacheFile(ParseFile.State state) {
     if (state.url() == null) {
       return null;
     }
-    return new File(cachePath, state.url()+".tmp");
+    return new File(cachePath, state.url() + ".tmp");
   }
 
   public boolean isDataAvailable(ParseFile.State state) {
@@ -121,7 +121,7 @@ public ParseFile.State then(Task<JSONObject> task) throws Exception {
 
         return newState;
       }
-    }, Task.BACKGROUND_EXECUTOR);
+    }, ParseExecutors.io());
   }
 
   public Task<File> fetchAsync(
@@ -138,7 +138,7 @@ public Task<File> fetchAsync(
       public Boolean call() throws Exception {
         return cacheFile.exists();
       }
-    }, Task.BACKGROUND_EXECUTOR).continueWithTask(new Continuation<Boolean, Task<File>>() {
+    }, ParseExecutors.io()).continueWithTask(new Continuation<Boolean, Task<File>>() {
       @Override
       public Task<File> then(Task<Boolean> task) throws Exception {
         boolean result = task.getResult();
@@ -156,25 +156,16 @@ public Task<File> then(Task<Boolean> task) throws Exception {
         // this incomplete cacheFile
         final File tempFile = getTempFile(state);
 
-        return Task.call(new Callable<Void>() {
-          @Override
-          public Void call() throws Exception {
-            // If the last download is interrupted, there may be incomplete temp file in disk. So
-            // we need to clear it first.
-            ParseFileUtils.deleteQuietly(tempFile);
-            return null;
-          }
-        }).continueWithTask(new Continuation<Void, Task<Void>>() {
-          @Override
-          public Task<Void> then(Task<Void> task) throws Exception {
-            // network
-            final ParseAWSRequest request =
-                new ParseAWSRequest(ParseRequest.Method.GET, state.url(), tempFile);
+        // network
+        final ParseAWSRequest request =
+            new ParseAWSRequest(ParseRequest.Method.GET, state.url(), tempFile);
 
-            return request.executeAsync(
-                awsClient(), null, downloadProgressCallback, cancellationToken);
-          }
-        }).continueWithTask(new Continuation<Void, Task<File>>() {
+        // We do not need to delete the temp file since we always try to overwrite it
+        return request.executeAsync(
+            awsClient(),
+            null,
+            downloadProgressCallback,
+            cancellationToken).continueWithTask(new Continuation<Void, Task<File>>() {
           @Override
           public Task<File> then(Task<Void> task) throws Exception {
             // If the top-level task was cancelled, don't actually set the data -- just move on.
@@ -189,7 +180,7 @@ public Task<File> then(Task<Void> task) throws Exception {
             ParseFileUtils.moveFile(tempFile, cacheFile);
             return Task.forResult(cacheFile);
           }
-        });
+        }, ParseExecutors.io());
       }
     });
   }