用Java下载和存储带有校验和信息的文件

Question

We are building a service to front fetching remote static files to our android app. The service will give a readout of the current md5 checksum of a file. The concept is that we retain the static file on the device until the checksum changes. When the file changes, the service will return a different checksum and this is the trigger for the device to download the file again.

I was thinking of just laying the downloaded files down in the file system with a .md5 file next to each one. When the code starts up, I'd go over all the files and make a map of file_name (known to be unique) to checksum. Then on requests for a file I'd check the remote service (whose response would only be checked every few minutes) and compare the result against that in the map.

The more I thought about this, the more I thought someone must have already done it. So before I put time into this I was wondering if there was a project out there doing this. I did some searching but could not find any.

Answer 1

Yes, it's built into HTTP. You can use conditional requests and cache files based on ETags, Last-Modified, etc. If you are looking for a library that implements your particular caching scheme, it's a bit unlikely that one exists. Write one and share it on GitHub :)