Class FileDrop


  • public class FileDrop
    extends java.lang.Object
    This class makes it easy to drag and drop files from the operating system to a Java program. Any java.awt.Component can be dropped onto, but only javax.swing.JComponents will indicate the drop event with a changed border.

    To use this class, construct a new FileDrop by passing it the target component and a Listener to receive notification when file(s) have been dropped. Here is an example:

          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
     

    You can specify the border that will appear when files are being dragged by calling the constructor with a javax.swing.border.Border. Only JComponents will show any indication with a border.

    You can turn on some debugging features by passing a PrintStream object (such as System.out) into the full constructor. A null value will result in no extra debugging information being output.

    I'm releasing this code into the Public Domain. Enjoy.

    Original author: Robert Harder, rharder@usa.net

    Version:
    1.0
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      static interface  FileDrop.Listener
      Implement this inner interface to listen for when files are dropped.
    • Field Summary

      Fields 
      Modifier and Type Field Description
      private static java.awt.Color defaultBorderColor  
      private java.awt.dnd.DropTargetListener dropListener  
      private javax.swing.border.Border normalBorder  
      private static java.lang.Boolean supportsDnD
      Discover if the running JVM is modern enough to have drag and drop.
    • Constructor Summary

      Constructors 
      Constructor Description
      FileDrop​(java.awt.Component c, boolean recursive, FileDrop.Listener listener)
      Constructor with a default border and the option to recursively set drop targets.
      FileDrop​(java.awt.Component c, javax.swing.border.Border dragBorder, boolean recursive, FileDrop.Listener listener)
      Constructor with a specified border and the option to recursively set drop targets.
      FileDrop​(java.awt.Component c, javax.swing.border.Border dragBorder, FileDrop.Listener listener)
      Constructor with a specified border
      FileDrop​(java.awt.Component c, FileDrop.Listener listener)
      Constructs a FileDrop with a default light-blue border and, if c is a Container, recursively sets all elements contained within as drop targets, though only the top level container will change borders.
      FileDrop​(java.io.PrintStream out, java.awt.Component c, boolean recursive, FileDrop.Listener listener)
      Constructor with a default border, debugging optionally turned on and the option to recursively set drop targets.
      FileDrop​(java.io.PrintStream out, java.awt.Component c, javax.swing.border.Border dragBorder, boolean recursive, FileDrop.Listener listener)
      Full constructor with a specified border and debugging optionally turned on.
      FileDrop​(java.io.PrintStream out, java.awt.Component c, javax.swing.border.Border dragBorder, FileDrop.Listener listener)
      Constructor with a specified border and debugging optionally turned on.
      FileDrop​(java.io.PrintStream out, java.awt.Component c, FileDrop.Listener listener)
      Constructor with a default border and debugging optionally turned on.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      private boolean isDragOk​(java.io.PrintStream out, java.awt.dnd.DropTargetDragEvent evt)
      Determine if the dragged data is a file list.
      private static void log​(java.io.PrintStream out, java.lang.String message)
      Outputs message to out if it's not null.
      static void main​(java.lang.String[] args)
      Runs a sample program that shows dropped files
      private void makeDropTarget​(java.io.PrintStream out, java.awt.Component c, boolean recursive)  
      static boolean remove​(java.awt.Component c)
      Removes the drag-and-drop hooks from the component and optionally from the all children.
      static boolean remove​(java.io.PrintStream out, java.awt.Component c, boolean recursive)
      Removes the drag-and-drop hooks from the component and optionally from the all children.
      private static boolean supportsDnD()  
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Field Detail

      • normalBorder

        private transient javax.swing.border.Border normalBorder
      • dropListener

        private transient java.awt.dnd.DropTargetListener dropListener
      • supportsDnD

        private static java.lang.Boolean supportsDnD
        Discover if the running JVM is modern enough to have drag and drop.
      • defaultBorderColor

        private static java.awt.Color defaultBorderColor
    • Constructor Detail

      • FileDrop

        public FileDrop​(java.awt.Component c,
                        FileDrop.Listener listener)
        Constructs a FileDrop with a default light-blue border and, if c is a Container, recursively sets all elements contained within as drop targets, though only the top level container will change borders.
        Parameters:
        c - Component on which files will be dropped.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.awt.Component c,
                        boolean recursive,
                        FileDrop.Listener listener)
        Constructor with a default border and the option to recursively set drop targets. If your component is a java.awt.Container, then each of its children components will also listen for drops, though only the parent will change borders.
        Parameters:
        c - Component on which files will be dropped.
        recursive - Recursively set children as drop targets.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.io.PrintStream out,
                        java.awt.Component c,
                        FileDrop.Listener listener)
        Constructor with a default border and debugging optionally turned on. With Debugging turned on, more status messages will be displayed to out. A common way to use this constructor is with System.out or System.err. A null value for the parameter out will result in no debugging output.
        Parameters:
        out - PrintStream to record debugging info or null for no debugging.
        c - Component on which files will be dropped.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.io.PrintStream out,
                        java.awt.Component c,
                        boolean recursive,
                        FileDrop.Listener listener)
        Constructor with a default border, debugging optionally turned on and the option to recursively set drop targets. If your component is a java.awt.Container, 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 out. A common way to use this constructor is with System.out or System.err. A null value for the parameter out will result in no debugging output.
        Parameters:
        out - PrintStream to record debugging info or null for no debugging.
        c - Component on which files will be dropped.
        recursive - Recursively set children as drop targets.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.awt.Component c,
                        javax.swing.border.Border dragBorder,
                        FileDrop.Listener listener)
        Constructor with a specified border
        Parameters:
        c - Component on which files will be dropped.
        dragBorder - Border to use on JComponent when dragging occurs.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.awt.Component c,
                        javax.swing.border.Border dragBorder,
                        boolean recursive,
                        FileDrop.Listener listener)
        Constructor with a specified border and the option to recursively set drop targets. If your component is a java.awt.Container, then each of its children components will also listen for drops, though only the parent will change borders.
        Parameters:
        c - Component on which files will be dropped.
        dragBorder - Border to use on JComponent when dragging occurs.
        recursive - Recursively set children as drop targets.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.io.PrintStream out,
                        java.awt.Component c,
                        javax.swing.border.Border dragBorder,
                        FileDrop.Listener listener)
        Constructor with a specified border and debugging optionally turned on. With Debugging turned on, more status messages will be displayed to out. A common way to use this constructor is with System.out or System.err. A null value for the parameter out will result in no debugging output.
        Parameters:
        out - PrintStream to record debugging info or null for no debugging.
        c - Component on which files will be dropped.
        dragBorder - Border to use on JComponent when dragging occurs.
        listener - Listens for filesDropped.
        Since:
        1.0
      • FileDrop

        public FileDrop​(java.io.PrintStream out,
                        java.awt.Component c,
                        javax.swing.border.Border dragBorder,
                        boolean recursive,
                        FileDrop.Listener listener)
        Full constructor with a specified border and debugging optionally turned on. With Debugging turned on, more status messages will be displayed to out. A common way to use this constructor is with System.out or System.err. A null value for the parameter out will result in no debugging output.
        Parameters:
        out - PrintStream to record debugging info or null for no debugging.
        c - Component on which files will be dropped.
        dragBorder - Border to use on JComponent when dragging occurs.
        recursive - Recursively set children as drop targets.
        listener - Listens for filesDropped.
        Since:
        1.0
    • Method Detail

      • supportsDnD

        private static boolean supportsDnD()
      • makeDropTarget

        private void makeDropTarget​(java.io.PrintStream out,
                                    java.awt.Component c,
                                    boolean recursive)
      • isDragOk

        private boolean isDragOk​(java.io.PrintStream out,
                                 java.awt.dnd.DropTargetDragEvent evt)
        Determine if the dragged data is a file list.
      • log

        private static void log​(java.io.PrintStream out,
                                java.lang.String message)
        Outputs message to out if it's not null.
      • remove

        public static boolean remove​(java.awt.Component c)
        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 c if c is a Container.
        Parameters:
        c - The component to unregister as a drop target
        Since:
        1.0
      • remove

        public static boolean remove​(java.io.PrintStream out,
                                     java.awt.Component c,
                                     boolean recursive)
        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.
        Parameters:
        out - Optional PrintStream for logging drag and drop messages
        c - The component to unregister
        recursive - Recursively unregister components within a container
        Since:
        1.0
      • main

        public static void main​(java.lang.String[] args)
        Runs a sample program that shows dropped files