[SOLVED] Commons-Net FTPClient is not downloading files correctly

Commons-Net FTPClient is not downloading files correctly

Solved

It turned out I misunderstood what the available() method actually does, so I just altered the code that wrote the data to this:

int b = input.read();
while (b != -1) {
    output.write(b);
    b = input.read();
}

I'll work on a more efficient reading/writing method another time, for now I'm just glad I've it working. Thanks for the help!

Original Post

I'm using the Commons-Net library to interact with a server via FTP and I've come across a problem when I try downloading files from the server to the local machine. I don't know if this is a bug in Comments-Net.FTPClient, but it's infinitely more likely I'm just not using the library correctly. That said, I haven't been able to find a solution when I googled the problem and example code I have seen appears to use the same method for downloading files as I do.

Anyway, the actual problem is that some of the files downloaded are completely empty, when they should contain data. It happens at random, so every time I download all the files, different files end up being empty each time. I'm assuming there is a problem with the way I'm reading the data from the server or writing it to a file.

Here's the code:

// For each file
InputStream input = ftp.retrieveFileStream(sourcePath);
ftp.completePendingCommand();

OutputStream output = new FileOutputStream(new File(destinationPath));
while (input.available() > 0) {
    output.write(input.read());
}

input.close();
output.close();

I'm pretty new to networking, so am I just being silly and doing something really simple wrong?

Solution

You shouldn't be using input.available() as that just tells you how much input is available without blocking. Loop until end of file instead (i.e. until read() returns -1).

http://download.oracle.com/javase/6/docs/api/java/io/InputStream.html#read()

If efficiency is a concern you could also try reading more than one byte at a time.