[JAVA][SWING] Drag-and-drop 파일선택시 드레그 앤 드롭 구현

앵간한 사이트에 다 있는 Drag-and-drop 기능을 Java Swing 프로그렘으로는 만들 수 없을까? 하는 의문이 들었다 

바로 검색 

검색하면 정말 앵간한건 다 나온다.

https://code.i-harness.com/ko-kr/q/c60f0

링크 따라가 보면 또 링크가 되어 있다

http://www.iharder.net/current/java/filedrop/

가 보면 다운로드가 있다. 

filedrop-1.1.zip

다운받아서 압축을 풀면 

다음과 같이 6개의 파일이 보인다

프로젝트 하나 만들어서 그중 Example.java 파일과 FileDrop.java 을 한 packge안에 넣어두고 

Example.java 를 실행 시키면 그냥 실행된다

Example.java

 
/**
 * A simple example showing how to use {@link FileDrop}
 * 
 * @author Robert Harder, rob@iharder.net
 */
public class Example {
 
    /** Runs a sample program that shows dropped files */
    public static void main(String[] args) {
        javax.swing.JFrame frame = new javax.swing.JFrame("FileDrop");
        // javax.swing.border.TitledBorder dragBorder = new
        // javax.swing.border.TitledBorder( "Drop 'em" );
        final javax.swing.JTextArea text = new javax.swing.JTextArea();
        frame.getContentPane().add(new javax.swing.JScrollPane(text), java.awt.BorderLayout.CENTER);
 
        new FileDrop(System.out, text, /* dragBorder, */ new FileDrop.Listener() {
            public void filesDropped(java.io.File[] files) {
                for (int i = 0; i < files.length; i++) {
                    try {
                        text.append(files[i].getCanonicalPath() + "\n");
                    } // end try
                    catch (java.io.IOException e) {
                    }
                } // end for: through each dropped file
            } // end filesDropped
        }); // end FileDrop.Listener
 
        frame.setBounds(100, 100, 300, 400);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    } // end main
 
}
 

완전 깔끔한 코드 

아... import 가 없는 이유가 여기 있었내

FileDrop.java

 
import java.awt.datatransfer.DataFlavor;
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.PrintStream;
import java.io.Reader;
 
/**
 * This class makes it easy to drag and drop files from the operating system to
 * a Java program. Any <tt>java.awt.Component</tt> can be dropped onto, but only
 * <tt>javax.swing.JComponent</tt>s will indicate the drop event with a changed
 * border.
 * <p/>
 * To use this class, construct a new <tt>FileDrop</tt> by passing it the target
 * component and a <tt>Listener</tt> to receive notification when file(s) have
 * been dropped. Here is an example:
 * <p/>
 * <code><pre>
 *      JPanel myPanel = new JPanel();
 *      new FileDrop( myPanel, new FileDrop.Listener()
 *      {   public void filesDropped( java.io.File[] files )
 *          {   
 *              // handle file drop
 *              ...
 *          }   // end filesDropped
 *      }); // end FileDrop.Listener
 * </pre></code>
 * <p/>
 * You can specify the border that will appear when files are being dragged by
 * calling the constructor with a <tt>javax.swing.border.Border</tt>. Only
 * <tt>JComponent</tt>s will show any indication with a border.
 * <p/>
 * You can turn on some debugging features by passing a <tt>PrintStream</tt>
 * object (such as <tt>System.out</tt>) into the full constructor. A
 * <tt>null</tt> value will result in no extra debugging information being
 * output.
 * <p/>
 *
 * <p>
 * I'm releasing this code into the Public Domain. Enjoy.
 * </p>
 * <p>
 * <em>Original author: Robert Harder, rharder@usa.net</em>
 * </p>
 * <p>
 * 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
 * </p>
 *
 * @author Robert Harder
 * @author rharder@users.sf.net
 * @version 1.0.1
 */
public class FileDrop {
    private transient javax.swing.border.Border normalBorder;
    private transient java.awt.dnd.DropTargetListener dropListener;
 
    /** Discover if the running JVM is modern enough to have drag and drop. */
    private static Boolean supportsDnD;
 
    // Default border color
    private static java.awt.Color defaultBorderColor = new java.awt.Color(0f, 0f, 1f, 0.25f);
 
    /**
     * Constructs a {@link FileDrop} with a default light-blue border and, if
     * <var>c</var> is a {@link java.awt.Container}, recursively sets all elements
     * contained within as drop targets, though only the top level container will
     * change borders.
     *
     * @param c        Component on which files will be dropped.
     * @param listener Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.awt.Component c, final Listener listener) {
        this(null, // Logging stream
                c, // Drop target
                javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, defaultBorderColor), // Drag border
                true, // Recursive
                listener);
    } // end constructor
 
    /**
     * Constructor with a default border and the option to recursively set drop
     * targets. If your component is a <tt>java.awt.Container</tt>, then each of its
     * children components will also listen for drops, though only the parent will
     * change borders.
     *
     * @param c         Component on which files will be dropped.
     * @param recursive Recursively set children as drop targets.
     * @param listener  Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.awt.Component c, final boolean recursive, final Listener listener) {
        this(null, // Logging stream
                c, // Drop target
                javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, defaultBorderColor), // Drag border
                recursive, // Recursive
                listener);
    } // end constructor
 
    /**
     * Constructor with a default border and debugging optionally turned on. With
     * Debugging turned on, more status messages will be displayed to <tt>out</tt>.
     * A common way to use this constructor is with <tt>System.out</tt> or
     * <tt>System.err</tt>. A <tt>null</tt> value for the parameter <tt>out</tt>
     * will result in no debugging output.
     *
     * @param out      PrintStream to record debugging info or null for no
     *                 debugging.
     * @param out
     * @param c        Component on which files will be dropped.
     * @param listener Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.io.PrintStream out, final java.awt.Component c, final Listener listener) {
        this(out, // Logging stream
                c, // Drop target
                javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, defaultBorderColor), false, // Recursive
                listener);
    } // end constructor
 
    /**
     * Constructor with a default border, debugging optionally turned on and the
     * option to recursively set drop targets. If your component is a
     * <tt>java.awt.Container</tt>, then each of its children components will also
     * listen for drops, though only the parent will change borders. With Debugging
     * turned on, more status messages will be displayed to <tt>out</tt>. A common
     * way to use this constructor is with <tt>System.out</tt> or
     * <tt>System.err</tt>. A <tt>null</tt> value for the parameter <tt>out</tt>
     * will result in no debugging output.
     *
     * @param out       PrintStream to record debugging info or null for no
     *                  debugging.
     * @param out
     * @param c         Component on which files will be dropped.
     * @param recursive Recursively set children as drop targets.
     * @param listener  Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.io.PrintStream out, final java.awt.Component c, final boolean recursive,
            final Listener listener) {
        this(out, // Logging stream
                c, // Drop target
                javax.swing.BorderFactory.createMatteBorder(2, 2, 2, 2, defaultBorderColor), // Drag border
                recursive, // Recursive
                listener);
    } // end constructor
 
    /**
     * Constructor with a specified border
     *
     * @param c          Component on which files will be dropped.
     * @param dragBorder Border to use on <tt>JComponent</tt> when dragging occurs.
     * @param listener   Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.awt.Component c, final javax.swing.border.Border dragBorder, final Listener listener) {
        this(null, // Logging stream
                c, // Drop target
                dragBorder, // Drag border
                false, // Recursive
                listener);
    } // end constructor
 
    /**
     * Constructor with a specified border and the option to recursively set drop
     * targets. If your component is a <tt>java.awt.Container</tt>, then each of its
     * children components will also listen for drops, though only the parent will
     * change borders.
     *
     * @param c          Component on which files will be dropped.
     * @param dragBorder Border to use on <tt>JComponent</tt> when dragging occurs.
     * @param recursive  Recursively set children as drop targets.
     * @param listener   Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.awt.Component c, final javax.swing.border.Border dragBorder, final boolean recursive,
            final Listener listener) {
        this(null, c, dragBorder, recursive, listener);
    } // end constructor
 
    /**
     * Constructor with a specified border and debugging optionally turned on. With
     * Debugging turned on, more status messages will be displayed to <tt>out</tt>.
     * A common way to use this constructor is with <tt>System.out</tt> or
     * <tt>System.err</tt>. A <tt>null</tt> value for the parameter <tt>out</tt>
     * will result in no debugging output.
     *
     * @param out        PrintStream to record debugging info or null for no
     *                   debugging.
     * @param c          Component on which files will be dropped.
     * @param dragBorder Border to use on <tt>JComponent</tt> when dragging occurs.
     * @param listener   Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.io.PrintStream out, final java.awt.Component c,
            final javax.swing.border.Border dragBorder, final Listener listener) {
        this(out, // Logging stream
                c, // Drop target
                dragBorder, // Drag border
                false, // Recursive
                listener);
    } // end constructor
 
    /**
     * Full constructor with a specified border and debugging optionally turned on.
     * With Debugging turned on, more status messages will be displayed to
     * <tt>out</tt>. A common way to use this constructor is with
     * <tt>System.out</tt> or <tt>System.err</tt>. A <tt>null</tt> value for the
     * parameter <tt>out</tt> will result in no debugging output.
     *
     * @param out        PrintStream to record debugging info or null for no
     *                   debugging.
     * @param c          Component on which files will be dropped.
     * @param dragBorder Border to use on <tt>JComponent</tt> when dragging occurs.
     * @param recursive  Recursively set children as drop targets.
     * @param listener   Listens for <tt>filesDropped</tt>.
     * @since 1.0
     */
    public FileDrop(final java.io.PrintStream out, final java.awt.Component c,
            final javax.swing.border.Border dragBorder, final boolean recursive, final Listener listener) {
 
        if (supportsDnD()) { // Make a drop listener
            dropListener = new java.awt.dnd.DropTargetListener() {
                public void dragEnter(java.awt.dnd.DropTargetDragEvent evt) {
                    log(out, "FileDrop: dragEnter event.");
 
                    // Is this an acceptable drag event?
                    if (isDragOk(out, evt)) {
                        // If it's a Swing component, set its border
                        if (c instanceof javax.swing.JComponent) {
                            javax.swing.JComponent jc = (javax.swing.JComponent) c;
                            normalBorder = jc.getBorder();
                            log(out, "FileDrop: normal border saved.");
                            jc.setBorder(dragBorder);
                            log(out, "FileDrop: drag border set.");
                        } // end if: JComponent
 
                        // Acknowledge that it's okay to enter
                        // evt.acceptDrag( java.awt.dnd.DnDConstants.ACTION_COPY_OR_MOVE );
                        evt.acceptDrag(java.awt.dnd.DnDConstants.ACTION_COPY);
                        log(out, "FileDrop: event accepted.");
                    } // end if: drag ok
                    else { // Reject the drag event
                        evt.rejectDrag();
                        log(out, "FileDrop: event rejected.");
                    } // end else: drag not ok
                } // end dragEnter
 
                public void dragOver(java.awt.dnd.DropTargetDragEvent evt) { // This is called continually as long as
                                                                                // the mouse is
                                                                                // over the drag target.
                } // end dragOver
 
                public void drop(java.awt.dnd.DropTargetDropEvent evt) {
                    log(out, "FileDrop: drop event.");
                    try { // Get whatever was dropped
                        java.awt.datatransfer.Transferable tr = evt.getTransferable();
 
                        // Is it a file list?
                        if (tr.isDataFlavorSupported(java.awt.datatransfer.DataFlavor.javaFileListFlavor)) {
                            // Say we'll take it.
                            // evt.acceptDrop ( java.awt.dnd.DnDConstants.ACTION_COPY_OR_MOVE );
                            evt.acceptDrop(java.awt.dnd.DnDConstants.ACTION_COPY);
                            log(out, "FileDrop: file list accepted.");
 
                            // Get a useful list
                            java.util.List fileList = (java.util.List) tr
                                    .getTransferData(java.awt.datatransfer.DataFlavor.javaFileListFlavor);
                            java.util.Iterator iterator = fileList.iterator();
 
                            // Convert list to array
                            java.io.File[] filesTemp = new java.io.File[fileList.size()];
                            fileList.toArray(filesTemp);
                            final java.io.File[] files = filesTemp;
 
                            // Alert listener to drop.
                            if (listener != null)
                                listener.filesDropped(files);
 
                            // Mark that drop is completed.
                            evt.getDropTargetContext().dropComplete(true);
                            log(out, "FileDrop: drop complete.");
                        } // end if: file list
                        else // this section will check for a reader flavor.
                        {
                            // Thanks, Nathan!
                            // BEGIN 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
                            DataFlavor[] flavors = tr.getTransferDataFlavors();
                            boolean handled = false;
                            for (int zz = 0; zz < flavors.length; zz++) {
                                if (flavors[zz].isRepresentationClassReader()) {
                                    // Say we'll take it.
                                    // evt.acceptDrop ( java.awt.dnd.DnDConstants.ACTION_COPY_OR_MOVE );
                                    evt.acceptDrop(java.awt.dnd.DnDConstants.ACTION_COPY);
                                    log(out, "FileDrop: reader accepted.");
 
                                    Reader reader = flavors[zz].getReaderForText(tr);
 
                                    BufferedReader br = new BufferedReader(reader);
 
                                    if (listener != null)
                                        listener.filesDropped(createFileArray(br, out));
 
                                    // Mark that drop is completed.
                                    evt.getDropTargetContext().dropComplete(true);
                                    log(out, "FileDrop: drop complete.");
                                    handled = true;
                                    break;
                                }
                            }
                            if (!handled) {
                                log(out, "FileDrop: not a file list or reader - abort.");
                                evt.rejectDrop();
                            }
                            // END 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
                        } // end else: not a file list
                    } // end try
                    catch (java.io.IOException io) {
                        log(out, "FileDrop: IOException - abort:");
                        io.printStackTrace(out);
                        evt.rejectDrop();
                    } // end catch IOException
                    catch (java.awt.datatransfer.UnsupportedFlavorException ufe) {
                        log(out, "FileDrop: UnsupportedFlavorException - abort:");
                        ufe.printStackTrace(out);
                        evt.rejectDrop();
                    } // end catch: UnsupportedFlavorException
                    finally {
                        // If it's a Swing component, reset its border
                        if (c instanceof javax.swing.JComponent) {
                            javax.swing.JComponent jc = (javax.swing.JComponent) c;
                            jc.setBorder(normalBorder);
                            log(out, "FileDrop: normal border restored.");
                        } // end if: JComponent
                    } // end finally
                } // end drop
 
                public void dragExit(java.awt.dnd.DropTargetEvent evt) {
                    log(out, "FileDrop: dragExit event.");
                    // If it's a Swing component, reset its border
                    if (c instanceof javax.swing.JComponent) {
                        javax.swing.JComponent jc = (javax.swing.JComponent) c;
                        jc.setBorder(normalBorder);
                        log(out, "FileDrop: normal border restored.");
                    } // end if: JComponent
                } // end dragExit
 
                public void dropActionChanged(java.awt.dnd.DropTargetDragEvent evt) {
                    log(out, "FileDrop: dropActionChanged event.");
                    // Is this an acceptable drag event?
                    if (isDragOk(out, evt)) { // evt.acceptDrag( java.awt.dnd.DnDConstants.ACTION_COPY_OR_MOVE );
                        evt.acceptDrag(java.awt.dnd.DnDConstants.ACTION_COPY);
                        log(out, "FileDrop: event accepted.");
                    } // end if: drag ok
                    else {
                        evt.rejectDrag();
                        log(out, "FileDrop: event rejected.");
                    } // end else: drag not ok
                } // end dropActionChanged
            }; // end DropTargetListener
 
            // Make the component (and possibly children) drop targets
            makeDropTarget(out, c, recursive);
        } // end if: supports dnd
        else {
            log(out, "FileDrop: Drag and drop is not supported with this JVM");
        } // end else: does not support DnD
    } // end constructor
 
    private static boolean supportsDnD() { // Static Boolean
        if (supportsDnD == null) {
            boolean support = false;
            try {
                Class arbitraryDndClass = Class.forName("java.awt.dnd.DnDConstants");
                support = true;
            } // end try
            catch (Exception e) {
                support = false;
            } // end catch
            supportsDnD = new Boolean(support);
        } // end if: first time through
        return supportsDnD.booleanValue();
    } // end supportsDnD
 
    // BEGIN 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
    private static String ZERO_CHAR_STRING = "" + (char) 0;
 
    private static File[] createFileArray(BufferedReader bReader, PrintStream out) {
        try {
            java.util.List list = new java.util.ArrayList();
            java.lang.String line = null;
            while ((line = bReader.readLine()) != null) {
                try {
                    // kde seems to append a 0 char to the end of the reader
                    if (ZERO_CHAR_STRING.equals(line))
                        continue;
 
                    java.io.File file = new java.io.File(new java.net.URI(line));
                    list.add(file);
                } catch (Exception ex) {
                    log(out, "Error with " + line + ": " + ex.getMessage());
                }
            }
 
            return (java.io.File[]) list.toArray(new File[list.size()]);
        } catch (IOException ex) {
            log(out, "FileDrop: IOException");
        }
        return new File[0];
    }
    // END 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
 
    private void makeDropTarget(final java.io.PrintStream out, final java.awt.Component c, boolean recursive) {
        // Make drop target
        final java.awt.dnd.DropTarget dt = new java.awt.dnd.DropTarget();
        try {
            dt.addDropTargetListener(dropListener);
        } // end try
        catch (java.util.TooManyListenersException e) {
            e.printStackTrace();
            log(out, "FileDrop: Drop will not work due to previous error. Do you have another listener attached?");
        } // end catch
 
        // Listen for hierarchy changes and remove the drop target when the parent gets
        // cleared out.
        c.addHierarchyListener(new java.awt.event.HierarchyListener() {
            public void hierarchyChanged(java.awt.event.HierarchyEvent evt) {
                log(out, "FileDrop: Hierarchy changed.");
                java.awt.Component parent = c.getParent();
                if (parent == null) {
                    c.setDropTarget(null);
                    log(out, "FileDrop: Drop target cleared from component.");
                } // end if: null parent
                else {
                    new java.awt.dnd.DropTarget(c, dropListener);
                    log(out, "FileDrop: Drop target added to component.");
                } // end else: parent not null
            } // end hierarchyChanged
        }); // end hierarchy listener
        if (c.getParent() != null)
            new java.awt.dnd.DropTarget(c, dropListener);
 
        if (recursive && (c instanceof java.awt.Container)) {
            // Get the container
            java.awt.Container cont = (java.awt.Container) c;
 
            // Get it's components
            java.awt.Component[] comps = cont.getComponents();
 
            // Set it's components as listeners also
            for (int i = 0; i < comps.length; i++)
                makeDropTarget(out, comps[i], recursive);
        } // end if: recursively set components as listener
    } // end dropListener
 
    /** Determine if the dragged data is a file list. */
    private boolean isDragOk(final java.io.PrintStream out, final java.awt.dnd.DropTargetDragEvent evt) {
        boolean ok = false;
 
        // Get data flavors being dragged
        java.awt.datatransfer.DataFlavor[] flavors = evt.getCurrentDataFlavors();
 
        // See if any of the flavors are a file list
        int i = 0;
        while (!ok && i < flavors.length) {
            // BEGIN 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
            // Is the flavor a file list?
            final DataFlavor curFlavor = flavors[i];
            if (curFlavor.equals(java.awt.datatransfer.DataFlavor.javaFileListFlavor)
                    || curFlavor.isRepresentationClassReader()) {
                ok = true;
            }
            // END 2007-09-12 Nathan Blomquist -- Linux (KDE/Gnome) support added.
            i++;
        } // end while: through flavors
 
        // If logging is enabled, show data flavors
        if (out != null) {
            if (flavors.length == 0)
                log(out, "FileDrop: no data flavors.");
            for (i = 0; i < flavors.length; i++)
                log(out, flavors[i].toString());
        } // end if: logging enabled
 
        return ok;
    } // end isDragOk
 
    /** Outputs <tt>message</tt> to <tt>out</tt> if it's not null. */
    private static void log(java.io.PrintStream out, String message) { // Log message if requested
        if (out != null)
            out.println(message);
    } // end log
 
    /**
     * Removes the drag-and-drop hooks from the component and optionally from the
     * all children. You should call this if you add and remove components after
     * you've set up the drag-and-drop. This will recursively unregister all
     * components contained within <var>c</var> if <var>c</var> is a
     * {@link java.awt.Container}.
     *
     * @param c The component to unregister as a drop target
     * @since 1.0
     */
    public static boolean remove(java.awt.Component c) {
        return remove(null, c, true);
    } // end remove
 
    /**
     * Removes the drag-and-drop hooks from the component and optionally from the
     * all children. You should call this if you add and remove components after
     * you've set up the drag-and-drop.
     *
     * @param out       Optional {@link java.io.PrintStream} for logging drag and
     *                  drop messages
     * @param c         The component to unregister
     * @param recursive Recursively unregister components within a container
     * @since 1.0
     */
    public static boolean remove(java.io.PrintStream out, java.awt.Component c, boolean recursive) { // Make sure we
                                                                                                        // support dnd.
        if (supportsDnD()) {
            log(out, "FileDrop: Removing drag-and-drop hooks.");
            c.setDropTarget(null);
            if (recursive && (c instanceof java.awt.Container)) {
                java.awt.Component[] comps = ((java.awt.Container) c).getComponents();
                for (int i = 0; i < comps.length; i++)
                    remove(out, comps[i], recursive);
                return true;
            } // end if: recursive
            else
                return false;
        } // end if: supports DnD
        else
            return false;
    } // end remove
 
    /* ******** I N N E R I N T E R F A C E L I S T E N E R ******** */
 
    /**
     * Implement this inner interface to listen for when files are dropped. For
     * example your class declaration may begin like this: <code><pre>
     *      public class MyClass implements FileDrop.Listener
     *      ...
     *      public void filesDropped( java.io.File[] files )
     *      {
     *          ...
     *      }   // end filesDropped
     *      ...
     * </pre></code>
     *
     * @since 1.1
     */
    public static interface Listener {
 
        /**
         * This method is called when files have been successfully dropped.
         *
         * @param files An array of <tt>File</tt>s that were dropped.
         * @since 1.0
         */
        public abstract void filesDropped(java.io.File[] files);
 
    } // end inner-interface Listener
 
    /* ******** I N N E R C L A S S ******** */
 
    /**
     * This is the event that is passed to the {@link FileDropListener#filesDropped
     * filesDropped(...)} method in your {@link FileDropListener} when files are
     * dropped onto a registered drop target.
     *
     * <p>
     * I'm releasing this code into the Public Domain. Enjoy.
     * </p>
     * 
     * @author Robert Harder
     * @author rob@iharder.net
     * @version 1.2
     */
    public static class Event extends java.util.EventObject {
 
        private java.io.File[] files;
 
        /**
         * Constructs an {@link Event} with the array of files that were dropped and the
         * {@link FileDrop} that initiated the event.
         *
         * @param files The array of files that were dropped
         * @source The event source
         * @since 1.1
         */
        public Event(java.io.File[] files, Object source) {
            super(source);
            this.files = files;
        } // end constructor
 
        /**
         * Returns an array of files that were dropped on a registered drop target.
         *
         * @return array of files that were dropped
         * @since 1.1
         */
        public java.io.File[] getFiles() {
            return files;
        } // end getFiles
 
    } // end inner class Event
 
    /* ******** I N N E R C L A S S ******** */
 
    /**
     * At last an easy way to encapsulate your custom objects for dragging and
     * dropping in your Java programs! When you need to create a
     * {@link java.awt.datatransfer.Transferable} object, use this class to wrap
     * your object. For example:
     * 
     * <pre>
     * <code>
     *      ...
     *      MyCoolClass myObj = new MyCoolClass();
     *      Transferable xfer = new TransferableObject( myObj );
     *      ...
     * </code>
     * </pre>
     * 
     * Or if you need to know when the data was actually dropped, like when you're
     * moving data out of a list, say, you can use the
     * {@link TransferableObject.Fetcher} inner class to return your object Just in
     * Time. For example:
     * 
     * <pre>
     * <code>
     *      ...
     *      final MyCoolClass myObj = new MyCoolClass();
     *
     *      TransferableObject.Fetcher fetcher = new TransferableObject.Fetcher()
     *      {   public Object getObject(){ return myObj; }
     *      }; // end fetcher
     *
     *      Transferable xfer = new TransferableObject( fetcher );
     *      ...
     * </code>
     * </pre>
     *
     * The {@link java.awt.datatransfer.DataFlavor} associated with
     * {@link TransferableObject} has the representation class
     * <tt>net.iharder.dnd.TransferableObject.class</tt> and MIME type
     * <tt>application/x-net.iharder.dnd.TransferableObject</tt>. This data flavor
     * is accessible via the static {@link #DATA_FLAVOR} property.
     *
     *
     * <p>
     * I'm releasing this code into the Public Domain. Enjoy.
     * </p>
     * 
     * @author Robert Harder
     * @author rob@iharder.net
     * @version 1.2
     */
    public static class TransferableObject implements java.awt.datatransfer.Transferable {
        /**
         * The MIME type for {@link #DATA_FLAVOR} is
         * <tt>application/x-net.iharder.dnd.TransferableObject</tt>.
         *
         * @since 1.1
         */
        public final static String MIME_TYPE = "application/x-net.iharder.dnd.TransferableObject";
 
        /**
         * The default {@link java.awt.datatransfer.DataFlavor} for
         * {@link TransferableObject} has the representation class
         * <tt>net.iharder.dnd.TransferableObject.class</tt> and the MIME type
         * <tt>application/x-net.iharder.dnd.TransferableObject</tt>.
         *
         * @since 1.1
         */
        public final static java.awt.datatransfer.DataFlavor DATA_FLAVOR = new java.awt.datatransfer.DataFlavor(
                FileDrop.TransferableObject.class, MIME_TYPE);
 
        private Fetcher fetcher;
        private Object data;
 
        private java.awt.datatransfer.DataFlavor customFlavor;
 
        /**
         * Creates a new {@link TransferableObject} that wraps <var>data</var>. Along
         * with the {@link #DATA_FLAVOR} associated with this class, this creates a
         * custom data flavor with a representation class determined from
         * <code>data.getClass()</code> and the MIME type
         * <tt>application/x-net.iharder.dnd.TransferableObject</tt>.
         *
         * @param data The data to transfer
         * @since 1.1
         */
        public TransferableObject(Object data) {
            this.data = data;
            this.customFlavor = new java.awt.datatransfer.DataFlavor(data.getClass(), MIME_TYPE);
        } // end constructor
 
        /**
         * Creates a new {@link TransferableObject} that will return the object that is
         * returned by <var>fetcher</var>. No custom data flavor is set other than the
         * default {@link #DATA_FLAVOR}.
         *
         * @see Fetcher
         * @param fetcher The {@link Fetcher} that will return the data object
         * @since 1.1
         */
        public TransferableObject(Fetcher fetcher) {
            this.fetcher = fetcher;
        } // end constructor
 
        /**
         * Creates a new {@link TransferableObject} that will return the object that is
         * returned by <var>fetcher</var>. Along with the {@link #DATA_FLAVOR}
         * associated with this class, this creates a custom data flavor with a
         * representation class <var>dataClass</var> and the MIME type
         * <tt>application/x-net.iharder.dnd.TransferableObject</tt>.
         *
         * @see Fetcher
         * @param dataClass The {@link java.lang.Class} to use in the custom data flavor
         * @param fetcher   The {@link Fetcher} that will return the data object
         * @since 1.1
         */
        public TransferableObject(Class dataClass, Fetcher fetcher) {
            this.fetcher = fetcher;
            this.customFlavor = new java.awt.datatransfer.DataFlavor(dataClass, MIME_TYPE);
        } // end constructor
 
        /**
         * Returns the custom {@link java.awt.datatransfer.DataFlavor} associated with
         * the encapsulated object or <tt>null</tt> if the {@link Fetcher} constructor
         * was used without passing a {@link java.lang.Class}.
         *
         * @return The custom data flavor for the encapsulated object
         * @since 1.1
         */
        public java.awt.datatransfer.DataFlavor getCustomDataFlavor() {
            return customFlavor;
        } // end getCustomDataFlavor
 
        /* ******** T R A N S F E R A B L E M E T H O D S ******** */
 
        /**
         * Returns a two- or three-element array containing first the custom data
         * flavor, if one was created in the constructors, second the default
         * {@link #DATA_FLAVOR} associated with {@link TransferableObject}, and third
         * the {@link java.awt.datatransfer.DataFlavor.stringFlavor}.
         *
         * @return An array of supported data flavors
         * @since 1.1
         */
        public java.awt.datatransfer.DataFlavor[] getTransferDataFlavors() {
            if (customFlavor != null)
                return new java.awt.datatransfer.DataFlavor[] { customFlavor, DATA_FLAVOR,
                        java.awt.datatransfer.DataFlavor.stringFlavor }; // end flavors array
            else
                return new java.awt.datatransfer.DataFlavor[] { DATA_FLAVOR,
                        java.awt.datatransfer.DataFlavor.stringFlavor }; // end flavors array
        } // end getTransferDataFlavors
 
        /**
         * Returns the data encapsulated in this {@link TransferableObject}. If the
         * {@link Fetcher} constructor was used, then this is when the
         * {@link Fetcher#getObject getObject()} method will be called. If the requested
         * data flavor is not supported, then the {@link Fetcher#getObject getObject()}
         * method will not be called.
         *
         * @param flavor The data flavor for the data to return
         * @return The dropped data
         * @since 1.1
         */
        public Object getTransferData(java.awt.datatransfer.DataFlavor flavor)
                throws java.awt.datatransfer.UnsupportedFlavorException, java.io.IOException {
            // Native object
            if (flavor.equals(DATA_FLAVOR))
                return fetcher == null ? data : fetcher.getObject();
 
            // String
            if (flavor.equals(java.awt.datatransfer.DataFlavor.stringFlavor))
                return fetcher == null ? data.toString() : fetcher.getObject().toString();
 
            // We can't do anything else
            throw new java.awt.datatransfer.UnsupportedFlavorException(flavor);
        } // end getTransferData
 
        /**
         * Returns <tt>true</tt> if <var>flavor</var> is one of the supported flavors.
         * Flavors are supported using the <code>equals(...)</code> method.
         *
         * @param flavor The data flavor to check
         * @return Whether or not the flavor is supported
         * @since 1.1
         */
        public boolean isDataFlavorSupported(java.awt.datatransfer.DataFlavor flavor) {
            // Native object
            if (flavor.equals(DATA_FLAVOR))
                return true;
 
            // String
            if (flavor.equals(java.awt.datatransfer.DataFlavor.stringFlavor))
                return true;
 
            // We can't do anything else
            return false;
        } // end isDataFlavorSupported
 
        /* ******** I N N E R I N T E R F A C E F E T C H E R ******** */
 
        /**
         * Instead of passing your data directly to the {@link TransferableObject}
         * constructor, you may want to know exactly when your data was received in case
         * you need to remove it from its source (or do anyting else to it). When the
         * {@link #getTransferData getTransferData(...)} method is called on the
         * {@link TransferableObject}, the {@link Fetcher}'s {@link #getObject
         * getObject()} method will be called.
         *
         * @author Robert Harder
         * @copyright 2001
         * @version 1.1
         * @since 1.1
         */
        public static interface Fetcher {
            /**
             * Return the object being encapsulated in the {@link TransferableObject}.
             *
             * @return The dropped object
             * @since 1.1
             */
            public abstract Object getObject();
        } // end inner interface Fetcher
 
    } // end class TransferableObject
 
} // end class FileDrop
 

주석이 절반 이상 ... 감사한대 영어라는거 ... ;; 아 ... 

한번 추가한 파일을 또 다시 추가하는 경우의 체크로직은 없다

다시말해 현재는 중복 추가가 가능하다는거

끝