Improves the readability of the backup code a bit

src/main/java/net/knarcraft/minecraftserverlauncher/userinterface/BackupGUI.java

@@ -75,19 +75,19 @@ public class BackupGUI implements ActionListener {
      * Destroys the backup GUI
      */
     public static void destroy() {
-        BackupUtil.abortBackup();
-        progressTextArea = null;
-        progressBar = null;
-        cancelButton = null;
         if (frame != null) {
             frame.dispose();
+            frame = null;
+            progressBar = null;
+            progressTextArea = null;
+            cancelButton = null;
         }
-        frame = null;
     }
 
     @Override
     public void actionPerformed(ActionEvent actionEvent) {
         if (actionEvent.getSource() == cancelButton) {
+            BackupUtil.abortBackup();
             destroy();
         }
     }

src/main/java/net/knarcraft/minecraftserverlauncher/utility/BackupUtil.java

@@ -36,18 +36,21 @@ public class BackupUtil {
     /**
      * Recursively copies a folder to another location
      *
-     * @param source      <p>The folder to copy</p>
-     * @param destination <p>Target destination</p>
+     * @param source         <p>The folder to copy</p>
+     * @param destination    <p>Target destination</p>
+     * @param backupFileSize <p>The total file size of the backup in progress</p>
+     * @param alreadyCopied  <p>The amount of bytes already copied</p>
      * @throws IOException <p>If we can't start a file stream</p>
      */
-    private static synchronized long backupFolder(File source, File destination, long backupFileSize, long alreadyCopied) throws IOException {
+    private static synchronized long backupFolder(File source, File destination, long backupFileSize,
+                                                  long alreadyCopied) throws IOException {
         if (backupAborted) {
             return 0L;
         }
         if (!source.isDirectory()) {
             long copiedFileSize = copyFile(source, destination);
             BackupGUI.updateProgress("Copying " + source + "\n to " + destination,
-                    (int)((alreadyCopied + copiedFileSize) * 100 / backupFileSize));
+                    (int) ((alreadyCopied + copiedFileSize) * 100 / backupFileSize));
             return copiedFileSize;
         } else {
             if (!destination.exists() && !destination.mkdir()) {
@@ -62,7 +65,7 @@ public class BackupUtil {
                     copiedFilesSize += backupFolder(srcFile, destinationFile, backupFileSize,
                             alreadyCopied + copiedFilesSize);
                     BackupGUI.updateProgress("Copying " + source + "\n to " + destination,
-                            (int)((alreadyCopied + copiedFilesSize) * 100 / backupFileSize));
+                            (int) ((alreadyCopied + copiedFilesSize) * 100 / backupFileSize));
                 }
             }
             return copiedFilesSize;
@@ -72,8 +75,8 @@ public class BackupUtil {
     /**
      * Copies a file from one location to another
      *
-     * @param source            <p>The file to copy</p>
-     * @param destination       <p>The location of the copied file</p>
+     * @param source      <p>The file to copy</p>
+     * @param destination <p>The location of the copied file</p>
      * @throws IOException <p>If reading or writing fails</p>
      */
     private static long copyFile(File source, File destination) throws IOException {
@@ -91,6 +94,8 @@ public class BackupUtil {
 
     /**
      * Copies all server directories to a folder specified by the user
+     *
+     * @param gui <p>The GUI to use for informing the user</p>
      */
     public synchronized static void backup(GUI gui) {
         backupAborted = false;
@@ -116,46 +121,70 @@ public class BackupUtil {
 
         gui.setStatus("Backing up " + (backupFileSize / 1000000) + "MB");
 
+        performBackup(gui, serverFolders, backupFileSize);
+    }
+
+    /**
+     * Performs the actual backup after checks have passed and necessary info is available
+     * @param gui <p>The GUI to use for informing the user</p>
+     * @param serverFolders <p>The folders of the servers to backup</p>
+     * @param backupFileSize <p>The total size of the folders to backup</p>
+     */
+    private static void performBackup(GUI gui, List<List<File>> serverFolders, long backupFileSize) {
         new BackupGUI();
         BackupGUI.updateProgress("Backup starting...", 0);
         long alreadyCopied = 0;
         for (List<File> serverFolder : serverFolders) {
-            if (backupAborted) {
+            if (backupAborted || !backupRunning) {
                 gui.setStatus("Backup aborted");
                 backupRunning = false;
                 return;
             }
-            File srcFolder = serverFolder.get(0);
-            File destinationFolder = serverFolder.get(1);
-
-            //Create child folders
-            if (!destinationFolder.exists() && !destinationFolder.mkdirs()) {
-                backupRunning = false;
-                gui.logError("Unable to create necessary sub-folder in the backup folder");
-                throw new IllegalArgumentException("Unable to create necessary sub-folder in the backup folder");
-            }
-            //Backup
-            try {
-                alreadyCopied += backupFolder(srcFolder, destinationFolder, backupFileSize, alreadyCopied);
-            } catch (IOException e) {
-                e.printStackTrace();
-                gui.setStatus("Backup caused an error");
-                backupRunning = false;
-            }
+            alreadyCopied = backupServerFiles(gui, serverFolder, backupFileSize, alreadyCopied);
         }
         backupRunning = false;
-        BackupGUI.destroy();
         if (backupAborted) {
             gui.setStatus("Backup aborted");
         } else {
+            BackupGUI.destroy();
             gui.setStatus("Backup finished");
         }
     }
 
+    /**
+     * Backs up the files for a single server
+     *
+     * @param gui <p>The GUI to use for informing the user</p>
+     * @param serverFolder <p>The server's input and output folders</p>
+     * @param backupFileSize <p>The total size of the files to backup</p>
+     * @param alreadyCopied <p>The amount of bytes already copied</p>
+     * @return <p>The new amount of bytes copied</p>
+     */
+    private static long backupServerFiles(GUI gui, List<File> serverFolder, long backupFileSize, long alreadyCopied) {
+        File srcFolder = serverFolder.get(0);
+        File destinationFolder = serverFolder.get(1);
+
+        //Create child folders
+        if (!destinationFolder.exists() && !destinationFolder.mkdirs()) {
+            backupRunning = false;
+            gui.logError("Unable to create necessary sub-folder in the backup folder");
+            throw new IllegalArgumentException("Unable to create necessary sub-folder in the backup folder");
+        }
+        //Backup
+        try {
+            alreadyCopied += backupFolder(srcFolder, destinationFolder, backupFileSize, alreadyCopied);
+        } catch (IOException e) {
+            e.printStackTrace();
+            gui.setStatus("Backup caused an error");
+            backupRunning = false;
+        }
+        return alreadyCopied;
+    }
+
     /**
      * Gets the size of a list of folders
      *
-     * @param gui <p>The GUI to write any errors to</p>
+     * @param gui           <p>The GUI to write any errors to</p>
      * @param serverFolders <p>The folder to find the size of</p>
      * @return <p>The size of the given folders</p>
      */
@@ -208,6 +237,7 @@ public class BackupUtil {
 
     /**
      * Gets the size of a file given its path
+     *
      * @param path <p>The path to a file</p>
      * @return <p>The size of the file in bytes, or 0 if an exception is thrown</p>
      */