Editor Drop Target 3 : Drag Drop « Swing JFC « Java

Editor Drop Target 3

Editor Drop Target 3
Core SWING Advanced Programming 
By Kim Topley
ISBN: 0 13 083292 8       
Publisher: Prentice Hall  

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Point;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.Transferable;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.awt.dnd.DnDConstants;
import java.awt.dnd.DropTarget;
import java.awt.dnd.DropTargetDragEvent;
import java.awt.dnd.DropTargetDropEvent;
import java.awt.dnd.DropTargetEvent;
import java.awt.dnd.DropTargetListener;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;

import javax.swing.JCheckBox;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;

public class EditorDropTarget3 implements DropTargetListener,
    PropertyChangeListener {
  public EditorDropTarget3(JEditorPane pane) {
    this.pane = pane;

    // Listen for changes in the enabled property

    // Save the JEditorPane's background color
    backgroundColor = pane.getBackground();

    // Create the DropTarget and register
    // it with the JEditorPane.
    dropTarget = new DropTarget(pane, DnDConstants.ACTION_COPY_OR_MOVE,
        this, pane.isEnabled(), null);

  // Implementation of the DropTargetListener interface
  public void dragEnter(DropTargetDragEvent dtde) {
    DnDUtils.debugPrintln("dragEnter, drop action = "
        + DnDUtils.showActions(dtde.getDropAction()));

    // Get the type of object being transferred and determine
    // whether it is appropriate.

    // Accept or reject the drag.
    boolean acceptedDrag = acceptOrRejectDrag(dtde);

    // Do drag-under feedback
    dragUnderFeedback(dtde, acceptedDrag);

  public void dragExit(DropTargetEvent dte) {
    DnDUtils.debugPrintln("DropTarget dragExit");

    // Do drag-under feedback
    dragUnderFeedback(null, false);

  public void dragOver(DropTargetDragEvent dtde) {
    DnDUtils.debugPrintln("DropTarget dragOver, drop action = "
        + DnDUtils.showActions(dtde.getDropAction()));

    // Accept or reject the drag
    boolean acceptedDrag = acceptOrRejectDrag(dtde);

    // Do drag-under feedback
    dragUnderFeedback(dtde, acceptedDrag);

  public void dropActionChanged(DropTargetDragEvent dtde) {
    DnDUtils.debugPrintln("DropTarget dropActionChanged, drop action = "
        + DnDUtils.showActions(dtde.getDropAction()));

    // Accept or reject the drag
    boolean acceptedDrag = acceptOrRejectDrag(dtde);

    // Do drag-under feedback
    dragUnderFeedback(dtde, acceptedDrag);

  public void drop(DropTargetDropEvent dtde) {
    DnDUtils.debugPrintln("DropTarget drop, drop action = "
        + DnDUtils.showActions(dtde.getDropAction()));

    // Check the drop action
    if ((dtde.getDropAction() & DnDConstants.ACTION_COPY_OR_MOVE) != 0) {
      // Accept the drop and get the transfer data
      Transferable transferable = dtde.getTransferable();

      try {
        boolean result = false;

        if (draggingFile) {
          result = dropFile(transferable);
        } else {
          result = dropContent(transferable, dtde);

        DnDUtils.debugPrintln("Drop completed, success: " + result);
      } catch (Exception e) {
        DnDUtils.debugPrintln("Exception while handling drop " + e);
    } else {
      DnDUtils.debugPrintln("Drop target rejected drop");

  // PropertyChangeListener interface
  public void propertyChange(PropertyChangeEvent evt) {
    String propertyName = evt.getPropertyName();
    if (propertyName.equals("enabled")) {
      // Enable the drop target if the JEditorPane is enabled
      // and vice versa.
    } else if (!changingBackground && propertyName.equals("background")) {
      backgroundColor = pane.getBackground();

  // Internal methods start here

  protected boolean acceptOrRejectDrag(DropTargetDragEvent dtde) {
    int dropAction = dtde.getDropAction();
    int sourceActions = dtde.getSourceActions();
    boolean acceptedDrag = false;

    DnDUtils.debugPrintln("\tSource actions are "
        + DnDUtils.showActions(sourceActions) + ", drop action is "
        + DnDUtils.showActions(dropAction));

    // Reject if the object being transferred
    // or the operations available are not acceptable.
    if (!acceptableType
        || (sourceActions & DnDConstants.ACTION_COPY_OR_MOVE) == 0) {
      DnDUtils.debugPrintln("Drop target rejecting drag");
    } else if (!draggingFile && !pane.isEditable()) {
      // Can't drag text to a read-only JEditorPane
      DnDUtils.debugPrintln("Drop target rejecting drag");
    } else if ((dropAction & DnDConstants.ACTION_COPY_OR_MOVE) == 0) {
      // Not offering copy or move - suggest a copy
      DnDUtils.debugPrintln("Drop target offering COPY");
      acceptedDrag = true;
    } else {
      // Offering an acceptable operation: accept
      DnDUtils.debugPrintln("Drop target accepting drag");
      acceptedDrag = true;

    return acceptedDrag;

  protected void dragUnderFeedback(DropTargetDragEvent dtde,
      boolean acceptedDrag) {
    if (draggingFile) {
      // When dragging a file, change the background color
      Color newColor = (dtde != null && acceptedDrag ? feedbackColor
          : backgroundColor);
      if (newColor.equals(pane.getBackground()) == false) {
        changingBackground = true;
        changingBackground = false;
    } else {
      if (dtde != null && acceptedDrag) {
        // Dragging text - move the insertion cursor
        Point location = dtde.getLocation();
      } else {

  protected void checkTransferType(DropTargetDragEvent dtde) {
    // Accept a list of files, or data content that
    // amounts to plain text or a Unicode text string
    acceptableType = false;
    draggingFile = false;
    if (dtde.isDataFlavorSupported(DataFlavor.javaFileListFlavor)) {
      acceptableType = true;
      draggingFile = true;
    } else if (dtde.isDataFlavorSupported(DataFlavor.plainTextFlavor)
        || dtde.isDataFlavorSupported(DataFlavor.stringFlavor)) {
      acceptableType = true;
    DnDUtils.debugPrintln("File type acceptable - " + acceptableType);
    DnDUtils.debugPrintln("Dragging a file - " + draggingFile);

  // This method handles a drop for a list of files
  protected boolean dropFile(Transferable transferable) throws IOException,
      UnsupportedFlavorException, MalformedURLException {
    List fileList = (List) transferable
    File transferFile = (File) fileList.get(0);
    final URL transferURL = transferFile.toURL();
    DnDUtils.debugPrintln("File URL is " + transferURL);


    return true;

  // This method handles a drop with data content
  protected boolean dropContent(Transferable transferable,
      DropTargetDropEvent dtde) {
    if (!pane.isEditable()) {
      // Can't drop content on a read-only text control
      return false;

    try {
      // Check for a match with the current content type
      DataFlavor[] flavors = dtde.getCurrentDataFlavors();

      DataFlavor selectedFlavor = null;

      // Look for either plain text or a String.
      for (int i = 0; i < flavors.length; i++) {
        DataFlavor flavor = flavors[i];
        DnDUtils.debugPrintln("Drop MIME type " + flavor.getMimeType()
            + " is available");
        if (flavor.equals(DataFlavor.plainTextFlavor)
            || flavor.equals(DataFlavor.stringFlavor)) {
          selectedFlavor = flavor;

      if (selectedFlavor == null) {
        // No compatible flavor - should never happen
        return false;


      DnDUtils.debugPrintln("Selected flavor is "
          + selectedFlavor.getHumanPresentableName());

      // Get the transferable and then obtain the data
      Object data = transferable.getTransferData(selectedFlavor);

      DnDUtils.debugPrintln("Transfer data type is "
          + data.getClass().getName());

      String insertData = null;
      if (data instanceof InputStream) {
        // Plain text flavor
        String charSet = selectedFlavor.getParameter("charset");
        InputStream is = (InputStream) data;
        byte[] bytes = new byte[is.available()];
        try {
          insertData = new String(bytes, charSet);
        } catch (UnsupportedEncodingException e) {
          // Use the platform default encoding
          insertData = new String(bytes);
      } else if (data instanceof String) {
        // String flavor
        insertData = (String) data;

      if (insertData != null) {
        int selectionStart = pane.getCaretPosition();
        pane.select(selectionStart, selectionStart
            + insertData.length());
        return true;
      return false;
    } catch (Exception e) {
      return false;

  public static void main(String[] args) {
    try {
    } catch (Exception evt) {}
    final JFrame f = new JFrame("JEditor Pane Drop Target Example 3");

    final JEditorPane pane = new JEditorPane();

    // Add a drop target to the JEditorPane
    EditorDropTarget3 target = new EditorDropTarget3(pane);

    f.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent evt) {

    JPanel panel = new JPanel();
    final JCheckBox editable = new JCheckBox("Editable");
    editable.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {

    final JCheckBox enabled = new JCheckBox("Enabled");
    enabled.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {

    f.getContentPane().add(new JScrollPane(pane), BorderLayout.CENTER);
    f.getContentPane().add(panel, BorderLayout.SOUTH);
    f.setSize(500, 400);

  protected JEditorPane pane;

  protected DropTarget dropTarget;

  protected boolean acceptableType; // Indicates whether data is acceptable

  protected boolean draggingFile; // True if dragging an entire file

  protected Color backgroundColor; // Original background color of JEditorPane

  protected boolean changingBackground;

  protected static final Color feedbackColor = Color.gray;

class DnDUtils {
  public static String showActions(int action) {
    String actions = "";
    if ((action & (DnDConstants.ACTION_LINK | DnDConstants.ACTION_COPY_OR_MOVE)) == 0) {
      return "None";

    if ((action & DnDConstants.ACTION_COPY) != 0) {
      actions += "Copy ";

    if ((action & DnDConstants.ACTION_MOVE) != 0) {
      actions += "Move ";

    if ((action & DnDConstants.ACTION_LINK) != 0) {
      actions += "Link";

    return actions;

  public static boolean isDebugEnabled() {
    return debugEnabled;

  public static void debugPrintln(String s) {
    if (debugEnabled) {

  private static boolean debugEnabled = (System
      .getProperty("DnDExamples.debug") != null);


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