1. Overview
In this quick tutorial, we’ll learn how to get the size of a file in Java – using Java 7, the new Java 8 and Apache Common IO.
Finally – we will also get a human readable representation of the file size.
2. Standard Java IO
Let’s start with a simple example of calculating the size of a file – using the File.length() method:
private long getFileSize(File file) {
long length = file.length();
return length;
}
We can test our implementation relatively simply:
@Test
public void whenGetFileSize_thenCorrect() {
long expectedSize = 12607;
File imageFile = new File("src/test/resources/image.jpg");
long size = getFileSize(imageFile);
assertEquals(expectedSize, size);
}
Note that, by default, the file sizes is calculated in bytes.
3. With Java NIO
Next – let’s see how to use the NIO library to get the size of the file.
In the following example, we’ll use the FileChannel.size() API to get the size of a file in bytes:
@Test
public void whenGetFileSizeUsingNioApi_thenCorrect() throws IOException {
long expectedSize = 12607;
Path imageFilePath = Paths.get("src/test/resources/image.jpg");
FileChannel imageFileChannel = FileChannel.open(imageFilePath);
long imageFileSize = imageFileChannel.size();
assertEquals(expectedSize, imageFileSize);
}
4. With Apache Commons IO
Next – let’s see how to get the file size using Apache Commons IO. In the following example – we simply use FileUtils.sizeOf() to get the file size:
@Test
public void whenGetFileSizeUsingApacheCommonsIO_thenCorrect() {
long expectedSize = 12607;
File imageFile = new File("src/test/resources/image.jpg");
long size = FileUtils.sizeOf(imageFile);
assertEquals(expectedSize, size);
}
Note that, for security restricted files, FileUtils.sizeOf() will report the size as zero.
5. Human Readable Size
Finally – let’s see how to get a more user readable representation of the file size using Apache Commons IO – not just a size in bytes:
@Test
public void whenGetReadableFileSize_thenCorrect() {
File imageFile = new File("src/test/resources/image.jpg");
long size = getFileSize(imageFile);
assertEquals("12 KB", FileUtils.byteCountToDisplaySize(size));
}
6. How to Get the Size of a File in MB, KB & GB in Java
To get the size of a file in megabytes (MB), kilobytes (KB), and gigabytes (GB) in Java, we need first to understand the relation between these units. It’s known that :
- 1 kilobyte (KB) = 1,024 bytes
- 1 megabyte (MB) = 1,024 KB
- gigabyte (GB) = 1,024 MB and
We can then conclude the following mathematical formulas to convert from a lower level of data size (e.g., bytes) to a higher level (e.g., kilobytes) and then to an even higher level (e.g., megabytes):
- Kilobytes = Bytes / 1024
- Megabytes = Kilobytes / 1024
- Gegabytes = Megabytes / 1024
let’s create a Java method that uses the previous mathematical formulas:
private void getSizeOfFile(String pathname) {
File file = new File(pathname);
if (file.exists()) {
// File size in bytes
long bytes = file.length();
double kilobytes = (double) bytes / 1024;
double megabytes = kilobytes / 1024;
double gigabytes = megabytes / 1024;
System.out.println("File size in bytes: " + bytes + " bytes");
System.out.println("File size in kilobytes: " + kilobytes + " KB");
System.out.println("File size in megabytes: " + megabytes + " MB");
System.out.println("File size in gigabytes: " + gigabytes + " GB");
} else {
System.out.println("File not found.");
}
}
The above code first checks if the file exists and if it does, it calculates and prints its size in bytes, kilobytes, megabytes, and gigabytes.
7. Conclusion
In this tutorial, we illustrated examples of using Java and Apache Commons IO to calculate the size of a file in the file system.
The implementation of these examples can be found in the GitHub project – this is a Maven-based project, so it should be easy to import and run as it is.
