Java进度栏帮助

Question

I need to implement a progress bar for the following task delay

FileOutputStream Fos= new FileOutputStream(FilePath);
byte buffer[]=Services.downloadFile(FilePath);
Fos.write(buffer);

Now, how can i know how much the file has been downloaded to update the progress bar

Answer 1

That's not easy since Services.downloadFile() doesn't give you the file in chunks. If you had a loop, it would be simple.

If you can change the API, I suggest to change it in this way:

Services.downloadFile(File, OutputStream);

and let downloadFile() write the file into the stream. Now you can wrap the stream and count the bytes written by overloading the various versions of write() .

[EDIT] I saw that Services is an RMI proxy. In this case, you can't use the approach above. Instead it gets more complex:

You need a pool of downloads on your server (think "Map"). The pool allows you to request another block of data for each download.

So on your server, you need:

1. Create an object that handles the download and which has a byte[] read() method.
2. Put the objects into a map with a key. Send the key to the client somehow.
3. For each object, create a thread that actually downloads the data and adds the data to a buffer. The read() method returns the content of the buffer and clears it.

On the client:

1. You need to call a method on the server to create a new download object and start the download thread.
2. Now you need a loop that calls read() on the download object on the server. The API is something like read(key) , the server looks up the key in the map and then calls read() on the download object.
3. Show the progress as you write the result of the read calls to the file