Counting the number of files in a directory using Java

java performance file directory
euphoria83 picture euphoria83 · Mar 26, 2009 · Viewed 137.2k times · Source

How do I count the number of files in a directory using Java ? For simplicity, lets assume that the directory doesn't have any sub-directories.

I know the standard method of :

new File(<directory path>).listFiles().length

But this will effectively go through all the files in the directory, which might take long if the number of files is large. Also, I don't care about the actual files in the directory unless their number is greater than some fixed large number (say 5000).

I am guessing, but doesn't the directory (or its i-node in case of Unix) store the number of files contained in it? If I could get that number straight away from the file system, it would be much faster. I need to do this check for every HTTP request on a Tomcat server before the back-end starts doing the real processing. Therefore, speed is of paramount importance.

I could run a daemon every once in a while to clear the directory. I know that, so please don't give me that solution.

Answer

Varkhan picture Varkhan · Mar 26, 2009

Ah... the rationale for not having a straightforward method in Java to do that is file storage abstraction: some filesystems may not have the number of files in a directory readily available... that count may not even have any meaning at all (see for example distributed, P2P filesystems, fs that store file lists as a linked list, or database-backed filesystems...). So yes,

new File(<directory path>).list().length

is probably your best bet.

Related questions

Very slow to generate MD5 for large file using Java

I am using Java to generate the MD5 hash for some files. I need to generate one MD5 for several files with a total size of about 1 gigabyte. Here's my code: private String generateMD5(SequenceInputStream inputStream){ if(inputStream==null){ return …

Read More
Why is processing a sorted array faster than processing an unsorted array?

Here is a piece of C++ code that shows some very peculiar behavior. For some strange reason, sorting the data miraculously makes the code almost six times faster: #include <algorithm> #include <ctime> #include <iostream> …

Read More
How can I read a large text file line by line using Java?

I need to read a large text file of around 5-6 GB line by line using Java. How can I do this quickly?

Read More