BAEL-7092: How to get the size of a file in MB, KB & GB in java (#15117)

* BAEL-7092: How to get the size of a file in MB, KB & GB in java

* Update JavaFileSizeUnitTest.java

* BAEL-7092: How to get the size of a file in MB, KB & GB in java

---------

Co-authored-by: Grzegorz Piwowarek <gpiwowarek@gmail.com>

core-java-modules/core-java-io/src/main/java/com/baeldung/size/FileSizeUtils.java

@@ -0,0 +1,28 @@
+package com.baeldung.size;
+
+import java.io.File;
+
+public class FileSizeUtils {
+    public static long getFileSizeInBytes(File file) {
+        if (file.exists()) {
+            return file.length();
+        } else {
+            throw new IllegalArgumentException("File not found.");
+        }
+    }
+
+    public static double getFileSizeInKilobytes(File file) {
+        long bytes = getFileSizeInBytes(file);
+        return (double) bytes / 1024;
+    }
+
+    public static double getFileSizeInMegabytes(File file) {
+        double kilobytes = getFileSizeInKilobytes(file);
+        return kilobytes / 1024;
+    }
+
+    public static double getFileSizeInGigabytes(File file) {
+        double megabytes = getFileSizeInMegabytes(file);
+        return megabytes / 1024;
+    }
+}