src/java/org/apache/log4j/chainsaw/dnd/FileDnDTarget.java

package org.apache.log4j.chainsaw.dnd;


import org.apache.log4j.Logger;
import java.awt.datatransfer.DataFlavor;
import java.awt.Color;
import java.awt.datatransfer.Transferable;
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.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.swing.BorderFactory;
import javax.swing.JComponent;

/**
 * This class provides all the functionality to work out when files are dragged onto
 * a particular JComponent instance, and then notifies listeners via
 * the standard PropertyChangesListener semantics to indicate that a list of 
 * files have been dropped onto the target.
 * 
 * If you wish to know whan the files have been dropped, subscribe to the "fileList" property change.
 * 
 * @author psmith
 *
 */
public class FileDnDTarget implements DropTargetListener{
    /**
     * Logger for this class
     */
    private static final Logger LOG = Logger.getLogger(FileDnDTarget.class);

    protected int acceptableActions = DnDConstants.ACTION_COPY;

    private DropTarget dropTarget;
    private List fileList;

    private JComponent guiTarget;
    private Map dropTargets = new HashMap();
    
    
    private PropertyChangeSupport propertySupport = new PropertyChangeSupport(this);
    /**
     * 
     */
    public FileDnDTarget(JComponent c) {
        this.guiTarget = c;
        dropTarget = new DropTarget(this.guiTarget, this);
    }
    
    public void addDropTargetToComponent(JComponent c){
        dropTargets.put(c, new DropTarget(c, this));
    }
    
    /**
     * @param listener
     */
    public void addPropertyChangeListener(PropertyChangeListener listener) {
        propertySupport.addPropertyChangeListener(listener);
    }
    /**
     * @param propertyName
     * @param listener
     */
    public void addPropertyChangeListener(String propertyName,
            PropertyChangeListener listener) {
        propertySupport.addPropertyChangeListener(propertyName, listener);
    }

    /**
     * 
     */
    private void decorateComponent() {
//        TODO work out a better way of decorating a component
        guiTarget.setBorder(BorderFactory.createLineBorder(Color.black));
    }


    public void dragEnter(DropTargetDragEvent e) {
        //LOG.debug(dtde);
        if (isDragOk(e) == false) {
            e.rejectDrag();
            return;
        }
        decorateComponent();

        e.acceptDrag(acceptableActions);
    }


    public void dragExit(DropTargetEvent dte) {
        removeComponentDecoration();
    }


    public void dragOver(DropTargetDragEvent e) {
        //LOG.debug(dtde);

        if (isDragOk(e) == false) {
            e.rejectDrag();
            return;
        }
        e.acceptDrag(acceptableActions);
    }

    public void drop(DropTargetDropEvent dtde) {
        Transferable transferable = dtde.getTransferable();
        LOG.debug(transferable);
        dtde.acceptDrop(acceptableActions);
        try {
            List list = (List)transferable.getTransferData(DataFlavor.javaFileListFlavor);
            LOG.debug(list);
            setFileList(list);
            dtde.getDropTargetContext().dropComplete(true);
            removeComponentDecoration();

        } catch (Exception e) {
            LOG.error("Error with DnD", e);
        }
        
    }

    public void dropActionChanged(DropTargetDragEvent dtde) {
        //LOG.debug(dtde);
    }
    /**
     * @return Returns the fileList.
     */
    public final List getFileList() {
        return fileList;
    }

    private boolean isDragOk(DropTargetDragEvent e) {
    	DataFlavor[] flavors = new DataFlavor[] { DataFlavor.javaFileListFlavor };
    	DataFlavor chosen = null;
    	for (int i = 0; i < flavors.length; i++) {
    		if (e.isDataFlavorSupported(flavors[i])) {
    			chosen = flavors[i];
    			break;
    		}
    	}
    	/*
    	 * the src does not support any of the StringTransferable flavors
    	 */
    	if (chosen == null) {
    		return false;
    	}
    	// the actions specified when the source
    	// created the DragGestureRecognizer
    	int sa = e.getSourceActions();
    
    	// we're saying that these actions are necessary
    	if ((sa & acceptableActions) == 0)
    		return false;
    	return true;
    }

    /**
     * 
     */
    private void removeComponentDecoration() {
        this.guiTarget.setBorder(null);
    }
    /**
     * @param listener
     */
    public void removePropertyChangeListener(PropertyChangeListener listener) {
        propertySupport.removePropertyChangeListener(listener);
    }
    /**
     * @param propertyName
     * @param listener
     */
    public void removePropertyChangeListener(String propertyName,
            PropertyChangeListener listener) {
        propertySupport.removePropertyChangeListener(propertyName, listener);
    }
    
    /**
     * @param fileList The fileList to set.
     */
    private  final void setFileList(List fileList) {
        Object oldValue = this.fileList;
        this.fileList = fileList;
        propertySupport.firePropertyChange("fileList", oldValue, this.fileList);
    }
}