Question

I want to make a Java downloader program, which will download the data from the url to some local default folder, such as /tmp/data.

However, if the url is like: http://www.site.com/book/1.html, I want to save the file 1.html into /tmp/data/book/1.html.

I don’t know how to mkdir recursively, by which I mean make the “book” folder automatically.

The code I make the program to make file is like this:

String dataDir = "/tmp/data";
URL url = new URL("http://www.site.com/book/1.html");
BufferedWriter bw = new BufferedWriter(new FileWriter(new File(dataDir+url.getFile())));
bw.write(data.toString());
bw.close();

Answer 1

You can use mkdirs:

File dataDir = new File("/tmp/data");
URL url = new URL("http://www.site.com/book/1.html");
final File targetFile = new File(dataDir, url.getFile());
final File targetDir = targetFile.getParentFile();
if (!targetDir.exists() && !targetDir.mkdirs()) {
    throw new SomeException("Failed to create parent directory " + targetDir);
}
// continue using targetFile

As you see I also use File to represent every path, for the sake of type safety and clearness.

Last but not least: if you simply download a HTML file, I’d not use a String to hold its content, because to get the correct String you’d need to know the HTML files encoding. It’s much easier to just handle it as a byte[], which avoids all the encoding-related problems.