I have an Android Service running daily which does some data synchronization. Once a day it downloads a file and caches it to disk via context.openFileOutput:
String fileName = Uri.parse(url).getLastPathSegment(); try (FileOutputStream outputStream = context.openFileOutput(fileName, Context.MODE_PRIVATE)) { outputStream.write(bytes); // ... } catch (IOException e) { // logging ... } This happens on a background thread. I also have a UI which contains a WebView. The WebView uses those cached resources if they are available via context.openFileInput:
@Override public WebResourceResponse shouldInterceptRequest( WebView view, WebResourceRequest request) { String url = request.getUrl().toString(); if (shouldUseCache(url)) { try { return new WebResourceResponse( "video/webm", Charsets.UTF_8.name(), context.openFileInput(obtainFileName(url))); } catch (IOException e) { // If a cached resource fails to load, just let the WebView load it the normal way. // logging ... } } return super.shouldInterceptRequest(view, request); } This happens on another background thread independently from the service.
Can I rely on Context implementation and be sure that file reads and writes are safe, or do I have to take care of the synchronization myself? E.g. if the Service is currently writing data to a file and the WebView is trying to access it, will I run into a problem? If so, how should I implement the synchronization?
1 Answers
Answers 1
If the Service is currently writing data to a file and the WebView is trying to access it, will I run into a problem?
In such cases you can write data to a file by appending something to file name and changing its name back once download is finished. e.g.
context.openFileOutput(fileName + ".downloading", Context.MODE_PRIVATE))
and later once download is finished rename the file to original fileName. I am sure you check for file presence in shouldUseCache(url) so it will keep working normally. This will avoid situations where a file is still downloading while you try to read it.
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