Intercepting web requests in JEditorPane

Question

How do I get the information about what is send to server when I click on a web link or a form submit button of a url loaded to a JEditorPane? I guess what I need is somehow to see what URLConnection object writes to server when URL openConnection() method is called. Any suggestions are very appreciated.
At the moment I can't even figure out how to intercept clicks on a form submit button. Adding HyperlinkListener clearly does not work and I dont see any other listeners for JEditorPane. The ultimate task is to see what is being set when a form is submitted.
Edited by: javiator on Dec 31, 2009 2:19 AM
Edited by: javiator on Dec 31, 2009 2:29 AM

Answer 1

Thank's for the advice. It actually looks better than the other sniffers I've downloaded. I've played around and here are some conclusions I've come to about JEditorPane. They may be correct or not. Thus any comments are welcome.
1. JEditorPane does not support directly form functionality. Therefore, working with forms is actually painful. But at least it responds to the clicks on submit button. The two problems I have to deal now are i. catch the click on the button event and ii. figure out when the new document has loaded. The solution I come up with by now is to catch the click event by implementing the PropertyChangeListener interface and then start a separate thread in which I just wait until JEditorPane text field contains a specific tag. Whenever that happens I consider that the page has loaded. That looks kinda lame but at the moment I don't see any other alternatives. Below is the ssce of the browser
package jlab.ssce.swing;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.event.HyperlinkEvent;
import javax.swing.event.HyperlinkListener;
import javax.swing.text.Document;
import javax.swing.text.html.HTMLDocument;
import javax.swing.text.html.HTMLEditorKit;
public class Browser extends JFrame implements HyperlinkListener, PropertyChangeListener {
     private HTMLDocumentLoader htmlDocumentLoader;
     private boolean hyperLinkEvent = false;
     private String isLoadedTag = "<div";
     private int maxLoadingTime = 1;
     public Browser() {
          htmlDocumentLoader = new HTMLDocumentLoader();
          setBrowser();
     public void setBrowser() {
          webPanel = new JPanel(new GridBagLayout());
          location = new JTextField();
          webPanel.add(location, new GridBagConstraints(0, 0, 1, 1, 100.0, 0.0
                 ,GridBagConstraints.CENTER, GridBagConstraints.HORIZONTAL, new Insets(5, 5, 5, 5), 0, 0));
          location.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent e){
                if(e.getKeyCode() == KeyEvent.VK_ENTER) {                     
                    actionGo();
     display_pane = new JEditorPane();
     display_pane.setContentType("text/html");
        display_pane.setEditable(false);
        display_pane.addHyperlinkListener(this);
        display_pane.addPropertyChangeListener(this);
        webPanel.add(new JScrollPane(display_pane), new GridBagConstraints(0, 1, 1, 1, 100.0, 100.0
                 ,GridBagConstraints.CENTER, GridBagConstraints.BOTH, new Insets(5, 5, 5, 5), 0, 0));
        getContentPane().add(webPanel);
        setSize(500, 400);
        setTitle("Browser");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);
     @Override
     public void hyperlinkUpdate(HyperlinkEvent e) {
          HyperlinkEvent.EventType etype = e.getEventType();
        if (etype == HyperlinkEvent.EventType.ACTIVATED) {
            hyperLinkEvent = true;
             loadHtmlDocument(e.getURL());
             hyperLinkEvent = false;
     @Override
     public void propertyChange(PropertyChangeEvent e) {
          try {
               if(!hyperLinkEvent) {
                    HTMLDocument htmlDoc = (HTMLDocument) e.getNewValue();
                    URL url = (URL) htmlDoc.getDocumentProperties().get("stream");
                    Thread loadingThread = new Thread(new LoaderClass(url));
                    loadingThread.start();
          } catch(Exception ex) {
     private void actionGo() {
        URL url;
          try {
               url = getProperUrl(location.getText());
               if(url == null) {
                    JOptionPane.showMessageDialog(null, "url " + location.getText() + " is not valid");
               } else {
                    hyperLinkEvent = true;
                    loadHtmlDocument(url);
                    hyperLinkEvent = false;
          } catch (Exception e) {
               e.printStackTrace();
     private URL getProperUrl(String url) {
          if(url.startsWith("http://") || url.startsWith("file:/")) {
               try {
                    return new URL(url);
               } catch (MalformedURLException e) {
                    return null;
          } else {
               return getClass().getClassLoader().getResource(url);
     private void loadHtmlDocument(URL url) {
          try {
               HTMLDocument htmlDoc = htmlDocumentLoader.loadDocument(url);
               location.setText(url.toString());
               display_pane.setDocument(htmlDoc);
          } catch (Exception e) {
               e.printStackTrace();
     private class LoaderClass implements Runnable {
          private URL url;
          public LoaderClass(URL url) {
               this.url = url;
          @Override
          public void run() {
               int loadingTime = 0;
               while(loadingTime < maxLoadingTime && !display_pane.getText().contains(isLoadedTag)) {
                    try {
                         Thread.sleep(1000);
                    } catch (InterruptedException e) {
                         e.printStackTrace();
                    loadingTime += 1;
               location.setText(url.toString());
     private static class HTMLDocumentLoader {          
          public HTMLDocument loadDocument(HTMLDocument doc, URL url, String charSet)
               throws IOException {
               doc.putProperty(Document.StreamDescriptionProperty, url);
               InputStream in = null;
               boolean ignoreCharSet = true;
               for (;;) {
                    try {
                         doc.remove(0, doc.getLength());
                         URLConnection urlc = url.openConnection();
                         in = urlc.getInputStream();
                         Reader reader = (charSet == null) ? new InputStreamReader(in)
                              : new InputStreamReader(in, charSet);
                         HTMLEditorKit.Parser parser = getParser();
                         HTMLEditorKit.ParserCallback htmlReader = getParserCallback(doc);
                         parser.parse(reader, htmlReader, ignoreCharSet);
                         htmlReader.flush();
                         break;
                    } catch (Exception ex) {
               return doc;
          public HTMLDocument loadDocument(URL url) throws IOException {
               return loadDocument((HTMLDocument) kit.createDefaultDocument(), url, null);
          public synchronized HTMLEditorKit.Parser getParser() {
               if (parser == null) {
                    try {
                         Class c = Class.forName("javax.swing.text.html.parser.ParserDelegator");
                         parser = (HTMLEditorKit.Parser) c.newInstance();
                    } catch (Throwable e) {
               return parser;
          public synchronized HTMLEditorKit.ParserCallback getParserCallback(
                    HTMLDocument doc) {
               return doc.getReader(0);
          protected static HTMLEditorKit kit;
          protected static HTMLEditorKit.Parser parser;
          static {
               kit = new HTMLEditorKit();
     public static void main(String[] args) {
          new Browser();
     JPanel
          webPanel;
     JEditorPane
          display_pane;
     JTextField 
          location;
}