Swing: Binding Hyperlinks to Actions

JEditorPane is the swing component which can display html pages. We can add a HyperLinkListener to JEditorPane to listen for any hyperlink events.

It is very easy to build a WebBrowser in Swing by a simple HyperLinkListener Implementation:

// @author Santhosh Kumar T - santhosh@in.fiorano.com 
public class HyperlinkActivator implements HyperlinkListener{
   public void hyperlinkUpdate(HyperlinkEvent e){
       if(e.getEventType()==HyperlinkEvent.EventType.ACTIVATED){
           try{
               ((JEditorPane)e.getSource()).setPage(e.getURL());
           } catch(Exception ex){
               ex.printStackTrace();
           }
       }
   }

}

There is nothing new in the above class. One such class is available directly in JEditorPane's
JavaDoc.


Now we will see how these hyperlinks can be used to invoke swing actions. Let us see the following screenshot from Microsoft Outlook's Message Rule Dialog:




Swing Components manage their list of action using ActionMap Let us see the class which binds hyperlinks with swing actions.:

// @author Santhosh Kumar T - santhosh@in.fiorano.com 
public class ActionBasedHyperlinkListener implements HyperlinkListener{
   ActionMap actionMap;

   public ActionBasedHyperlinkListener(ActionMap actionMap){
       this.actionMap = actionMap;
   }

   public void hyperlinkUpdate(HyperlinkEvent e){
       if(e.getEventType()!=HyperlinkEvent.EventType.ACTIVATED)
           return;
       String href = e.getDescription();
       Action action = actionMap.get(href);
       if(action!=null)
           action.actionPerformed(new ActionEvent(e, ActionEvent.ACTION_PERFORMED, href));
   }

}

When a hyperlinks gets activated, we get its href value from HyperLinkEvent and find the action with that key from actionMap. If any action is found, we perform that action.
Let us create a simple action which simulates the above screenshot:

// @author Santhosh Kumar T - santhosh@in.fiorano.com 
public class SelectPeopleAction extends AbstractAction{
   private final static String people[] = {"Santhosh", "Rick", "Matt", "Lorimer", "Scott"};

   public SelectPeopleAction(){
       super("selectPeople");
   }

   public void actionPerformed(ActionEvent e){
       HyperlinkEvent hle = (HyperlinkEvent)e.getSource();

       try{
           Element elem = hle.getSourceElement();
           Document doc = elem.getDocument();
           int start = elem.getStartOffset();
           int end = elem.getEndOffset();
           String link = doc.getText(start, end-start);
           link = link.equals("contains people") ? "" : link.substring("contains ".length());

           JList list = new JList(people);
           StringTokenizer stok = new StringTokenizer(link, ", ");
           while(stok.hasMoreTokens()){
               String token = stok.nextToken();
               for(int i = 0; i<list.getModel().getSize(); i++){
                   if(list.getModel().getElementAt(i).equals(token))
                       list.getSelectionModel().addSelectionInterval(i, i);
               }
           }

           int response = JOptionPane.showOptionDialog((Component)hle.getSource(), new JScrollPane(list), "People",
                   JOptionPane.OK_CANCEL_OPTION, JOptionPane.PLAIN_MESSAGE,
                   null, null, null);
           if(response==JOptionPane.OK_OPTION){
               String newLink = "";
               Object selected[] = list.getSelectedValues();
               for(int i = 0; i<selected.length; i++){
                   if(i!=0)
                       newLink += ", ";
                   newLink += selected[i];
               }
               newLink = newLink.length()==0 ? "contains people" : "contains "+newLink;
               elem.getDocument().remove(start, end-start);
               elem.getDocument().insertString(start, newLink, elem.getAttributes());
           }
       } catch(BadLocationException ex){
           ex.printStackTrace();
       }
   }

}

The above action will be activated when the hyperlink "contains people" is activated. It finds the text of hyperlink from the offsets got from hyperlink event. It then creates a JList with available people and selects the current people from the hyperlink text by tokenizing it. It pops up a dialog from which user can change the selected people. On this dialog's confirm, it computes the new text for hyperlink and updates the html accordingly.

From the above class, you learn:

1. How to fetch href attribute value from hyperlink
   
2. How to fetch hyperlink text.
   
3. How to modify html partially
   

Let us write the demo application:

// @author Santhosh Kumar T - santhosh@in.fiorano.com 
public class HyperLinksDemo extends JFrame{
   public HyperLinksDemo() throws Exception{
       super("Hyperlinks Demo - santhosh@in.fiorano.com");
       JEditorPane editor = new JEditorPane();
       editor.setPage(getClass().getResource("rule.html"));
       editor.setEditable(false);

       ActionMap actionMap = new ActionMap();
       actionMap.put("selectPeople", new SelectPeopleAction());
       editor.addHyperlinkListener(new ActionBasedHyperlinkListener(actionMap));

       JPanel contents = (JPanel)getContentPane();
       contents.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
       contents.add(new JScrollPane(editor));
       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       setSize(400, 300);
   }

   public static void main(String[] args) throws Exception{
       try{
           UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
       } catch(Exception e){
           e.printStackTrace();
       }
       new HyperLinksDemo().setVisible(true);
   }

}

This is the file rule.html used:


<html>

<body>


<p>When the newly arrived message arrives<br>

where the From <a href="selectPeople">


contains people</a><br>

delete it.</p>


</body>


</html>





When hyperlink is clicked it displays:





On confirming the above dialog: