package com.opensymphony.workflow.designer.swing;import java.awt.*;import java.awt.datatransfer.DataFlavor;import java.awt.datatransfer.Transferable;import java.awt.datatransfer.UnsupportedFlavorException;import java.awt.dnd.*;import java.awt.event.HierarchyEvent;import java.awt.event.HierarchyListener;import java.io.File;import java.io.IOException;import java.util.List;import java.util.TooManyListenersException;import javax.swing.*;public abstract class FileDropHandler{  private transient java.awt.dnd.DropTargetListener dropListener;  public FileDropHandler(Component target)  {    this(target, true);  }  public FileDropHandler(final Component target, final boolean recursive)  {    dropListener = new DropTargetListener()    {      public void dragEnter(DropTargetDragEvent evt)      {        if(isDragOk(evt))        {          evt.acceptDrag(DnDConstants.ACTION_COPY);        }        else        {          evt.rejectDrag();        }      }      public void dragOver(DropTargetDragEvent evt)      {}      public void drop(DropTargetDropEvent evt)      {        try        {          Transferable tr = evt.getTransferable();          if(tr.isDataFlavorSupported(DataFlavor.javaFileListFlavor))          {            evt.acceptDrop(DnDConstants.ACTION_COPY);            List fileList = (List)tr.getTransferData(DataFlavor.javaFileListFlavor);            File[] filesTemp = new File[fileList.size()];            fileList.toArray(filesTemp);            final File[] files = filesTemp;            filesDropped(files);            evt.getDropTargetContext().dropComplete(true);          }          else          {            evt.rejectDrop();          }        }        catch(IOException io)        {          io.printStackTrace();          evt.rejectDrop();        }        catch(UnsupportedFlavorException ufe)        {          ufe.printStackTrace();          evt.rejectDrop();        }      }      public void dragExit(DropTargetEvent evt)      {      }      public void dropActionChanged(DropTargetDragEvent evt)      {        if(isDragOk(evt))        {          evt.acceptDrag(DnDConstants.ACTION_COPY);        }        else        {          evt.rejectDrag();        }      }    };    makeDropTarget(target, recursive);  }  private void makeDropTarget(final Component target, boolean recursive)  {    final DropTarget dt = new DropTarget();    try    {      dt.addDropTargetListener(dropListener);    }    catch(TooManyListenersException e)    {      e.printStackTrace();    }    target.addHierarchyListener(new HierarchyListener()    {      public void hierarchyChanged(HierarchyEvent evt)      {        Component parent = target.getParent();        if(parent == null)        {          target.setDropTarget(null);        }        else        {          new DropTarget(target, dropListener);        }      }    });    if(target.getParent() != null)      new DropTarget(target, dropListener);    if(recursive && (target instanceof Container))    {      Container cont = (Container)target;      Component[] comps = cont.getComponents();      for(int i = 0; i < comps.length; i++)        makeDropTarget(comps[i], recursive);    }  }  private boolean isDragOk(final DropTargetDragEvent evt)  {    boolean ok = false;    DataFlavor[] flavors = evt.getCurrentDataFlavors();    int i = 0;    while(!ok && i < flavors.length)    {      if(flavors[i].equals(DataFlavor.javaFileListFlavor))        ok = true;      i++;    }    return ok;  }  public abstract void filesDropped(File[] files);  public static void main(String[] args)  {    JFrame frame = new JFrame("FileDrop");    final JTree tree = new JTree();    frame.getContentPane().add(new JScrollPane(tree), BorderLayout.CENTER);    new FileDropHandler(tree)    {      public void filesDropped(File[] files)      {        for(int i = 0; i < files.length; i++)        {          System.out.println("dropped " + files[i]);        }      }    };    frame.setBounds(100, 100, 300, 400);    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    frame.show();  }}