Commons-Net FTPClient 无法正确下载文件
解决
了事实证明我误解了 available() 方法的实际作用，所以我只是将写入数据的代码更改为：
int b = input.read();
while (b != -1) {
output.write(b);
b = input.read();
}
我将再次研究更有效的读/写方法，现在我很高兴我已经它工作了。感谢您的帮助！
原始帖子
我正在使用 Commons-Net 库通过 FTP 与服务器交互，当我尝试将文件从服务器下载到本地计算机时遇到问题。我不知道这是否是 Comments-Net.FTPClient 中的错误，但更有可能是我没有正确使用该库。也就是说，当我用谷歌搜索问题时，我一直无法找到解决方案，并且我看到的示例代码似乎使用与我相同的方法来下载文件。
无论如何，实际的问题是，某些下载的文件本应包含数据，但完全是空的。它是随机发生的，所以每次我下载所有文件时，每次都会有不同的文件最终为空。我假设我从服务器读取数据或将其写入文件的方式存在问题。
代码如下：
// 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();
我对网络还很陌生，所以我只是愚蠢地做了一些非常简单的错误吗？
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?
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评论（2）
您不应该使用 input.available() 因为它只是告诉您有多少输入可用而不阻塞。循环直到文件末尾（即直到 read() 返回 -1）。
http://download.oracle.com/javase /6/docs/api/java/io/InputStream.html#read()
如果效率是一个问题，您也可以尝试一次读取多个字节。
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.
使用
IOUtils和FileUtils查看 commons-io 以实现更简单的流处理Check out commons-io with
IOUtilsandFileUtilsfor simpler stream processing