Getting Size of File or Directory in Java

Learn to get the size of a file or a directory in Java using IO classes File, Files and Common IO’s FileUtils class.

1. Using Standard IO’s File.length()

To get the size of file, File class provides length() method that returns the length of the file in bytes.

We may get SecurityException if the read access to the file is denied.

If the file represents a directory then return value is unspecified.

File file = new File("c:/temp/demo.txt");

long bytes = file.length();

2. Using New IO’s Files.size()

The Files class provides a straightforward method size() that acts similar to previous example. It also returns the size of the file in bytes.

The size may differ from the actual size on the file system due to compression, support for sparse files, or other reasons.

This method also may throw SecurityException if the read access to the file is denied.

File file = new File("c:/temp/demo.txt");

long bytes = Files.size(file.toPath());

3. Using Commons IO’s FileUtils.sizeOf()

FileUtils.sizeOf() can be used to get the size of a file or directory.

If the file is a regular file then size of file is returned in bytes.
If the file is a directory then size of the directory is calculated recursively. Note that if there is any issue in reading any file or sub-directory then its size will not be included in the result.

We should be careful to check that ditectory shall not be too big because sizeOf() will not detect any overflow in the final size value and a negative value may be returned.

File file = new File("c:/temp/demo.txt");

long bytes = FileUtils.sizeOf(file);

4. Displaying Formatted Size

To display the size in a formatted manner to the end user, we may do the formatting ourselves or we can use the FileUtils.byteCountToDisplaySize() method.

4.1. Custom Formatting

Use the String.format() method to produce the formatted output strings as per requirements.

System.out.println(String.format("%,d Bytes", bytes));
System.out.println(String.format("%,d KB", bytes / 1024));

4.2. Using FileUtils.byteCountToDisplaySize()

The byteCountToDisplaySize() returns a human-readable version of the file size. Note that file size is rounded to the near KB, MB or GB.

System.out.println(FileUtils.byteCountToDisplaySize(2333444l));  //2 MB
System.out.println(FileUtils.byteCountToDisplaySize(2333444555l));  //2 GB

5. Conclusion

In this short tutorial, we learned to calculate the size of a file or directory in Java. We also saw how to format the file size for displaying to the user.

For regular files, we can use the Java IO classes. For calculating the size of directories, using Commons IO’s FileUtils is an excellent choice.

Happy Learning !!

Source Code on Github