What's the best way to monitor an InputStream?

Question

I'm reading a file in via apache.commons.FtpClient.

This works fine 99.9% of the time but sometimes it just dies in the read() method...

InputStream inStream = ftp.retrieveFileStream(path + file.getName());
String fileAsString = "";

if(inStream == null){
    return;
}
while((c = inStream.read()) != -1){ //this is where the code sometimes just hangs    
   fileAsString += Character.valueOf((char)c);

}

My question is what is the most reliable way to protect against this locking up the system indefinitely. Should I be setting a timer in a separate thread? Or is there a simpler way to do it?

Answer 1

Just from a quick look at the docs, if you did...

while (inStream.available() > 0 && (c = inStream.read()) != -1)

It seems like it would double check that you can read without blocking before you actually read. I'm not certain on this though.

Answer 2

If your code hangs it means your FTP server has not sent the entire file. You can use a Timer, but I believe FtpClient allows you to set a timeout.

BTW: the way you read the file is very inefficient. If your file is larger than a few K it will use increasing amounts of CPU.

You are creating a Character from a byte (which is a bad idea in itself) and a String object for every byte in the file.

I suggest using the copy method provided or the one which comes with commons-io library to copy the data to a ByteArrayInputStream.

Answer 3

The question "Is it possible to read from a Java InputStream with a timeout?" is related to this one.