Is it possible to upload data as a background process in j2me?

Question

Even with a poor network connection?

Specifically, I've written code which launches a separate thread (from the UI) that attempts to upload a file via HTTP POST. I've found, however, that if the connection is bad, the processor gets stuck on outputstream.close() or httpconnection.getheaderfield() or any read/write which forces data over the network. This causes not only the thread to get stuck, but steals the entire processor, so even the user interface becomes unresponsive.

I've tried lowering the priority of the thread, to no avail.

My theory is that there is no easy way of avoiding this behavior, which is why all the j2me tutorial instruct developers to create a ‘sending data over the network…’ screen, instead of just sending everything in a background thread. If someone can prove me wrong, that would be fantastic.

Thanks!

Answer 1

It pretty much depends on how you write the code and where you run it. On CLDC the concept of threading is pretty limited and if any thread is doing some long lasting operation other threads might be (and usualy are) blocked by it as well. You should take that into account when designing your application.

Answer 2

One important aspect is you need to have a generic UI or screen that can be displayed when the network call in background fails. It is pretty much a must on any mobile app, J2ME or otherwise.

As Honza said, it depends on the design, there are so many things that can be done, like pre-fetching data on app startup, or pre-fetching data based on the screen that is loaded (i.e navigation path), or having a default data set built in into the app etc.

Another thing that you can try is a built-in timer mechanism that retries data download after certain amount of time, and aborting after say 5 tries or 1-2 minutes and displaying generic screen or error message.

Certain handsets in J2ME allow detection of airplane mode, if possible you can detect that and promptly display an appropriate screen.

Also one design that has worked for me is synchronizing UI and networking threads, so that they dont lock up each other (take this bit of advice with heavy dose of salt as I have had quite a few interesting bugs on some samsung and sanyo handsets because of this)

All in all no good answer for you, but different strategies.

Answer 3

You can divide your file data into chunks and then upload with multiple retries on failure. This depends on your application strategy . If your priority is to upload a bulk data with out failure. You need to have assemble the chunks on server to build back your data . This may have the overhead for making connections but the chance is high for your data will get uploaded . If you are not uploading files concurrently this will work with ease .