In Java, you can use the File.length() method to get the file size in bytes.

Example

Get an image file (c:\\java_xml_logo.jpg) 14KB, and display the file size.

package com.mkyong.file;
 
import java.io.File;
 
public class FileSizeExample 
{
    public static void main(String[] args)
    {	
		File file =new File("c:\\java_xml_logo.jpg");
 
		if(file.exists()){
 
			double bytes = file.length();
			double kilobytes = (bytes / 1024);
			double megabytes = (kilobytes / 1024);
			double gigabytes = (megabytes / 1024);
			double terabytes = (gigabytes / 1024);
			double petabytes = (terabytes / 1024);
			double exabytes = (petabytes / 1024);
			double zettabytes = (exabytes / 1024);
			double yottabytes = (zettabytes / 1024);
 
			System.out.println("bytes : " + bytes);
			System.out.println("kilobytes : " + kilobytes);
			System.out.println("megabytes : " + megabytes);
			System.out.println("gigabytes : " + gigabytes);
			System.out.println("terabytes : " + terabytes);
			System.out.println("petabytes : " + petabytes);
			System.out.println("exabytes : " + exabytes);
			System.out.println("zettabytes : " + zettabytes);
			System.out.println("yottabytes : " + yottabytes);
		}else{
			 System.out.println("File does not exists!");
		}
 
    }
}

Result

bytes : 13900.0
kilobytes : 13.57421875
megabytes : 0.013256072998046875
gigabytes : 1.2945383787155151E-5
terabytes : 1.2641976354643703E-8
petabytes : 1.234568003383174E-11
exabytes : 1.205632815803881E-14
zettabytes : 1.1773757966834775E-17
yottabytes : 1.1497810514487085E-20