Question

I am trying to use JEditorPane to display some HTML text. For some reason I have to use setText() method. However that makes the JEditorPane flickering. The reason is that every time after updating the editorPane.setText(msgBuffer); I have to bring the cursor to the end of document editorPane.setCaretPosition((editorPane.getDocument()).getLength()-1) asI want the most recent text line appearing at the bottom of the document.
I have bright you guys the entire code for you to see it for yourself. I have seen many recommendations as to use document.insertString, but for that matter I have to use individual attributes which is not of my interest.
Is there any way to make this code run flicker free?

import javax.swing.JEditorPane;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.text.Document;
import javax.swing.text.html.HTMLEditorKit;
import javax.swing.text.html.StyleSheet;

public class CMessageWindow {

    private static final String ERROR   = "ERROR"; 
    private static final String MESSAGE = "msg";
    private  JScrollPane scrollPane;
    public  JEditorPane  editorPane;
    private  HTMLEditorKit kit;
    private  String msgBuffer=new String("");
    private static CMessageWindow window=null;
    private static JFrame frameContainer=null;

    private CMessageWindow()
    {
        editorPane  = new JEditorPane ();
        editorPane.setEditable(false);
        editorPane.setContentType("text/html");
        kit = new HTMLEditorKit();
        editorPane.setEditorKit(kit);

        StyleSheet styleSheet = kit.getStyleSheet();
        styleSheet.addRule("."+MESSAGE+" {font: 10px monaco; color: black; }");
        styleSheet.addRule("."+ERROR+" {font: 10px monaco; color: #ff2222; background-color : #cccccc; }");

        Document doc = kit.createDefaultDocument();
        editorPane.setDocument(doc);
        scrollPane = new JScrollPane(editorPane);
    }
    public static CMessageWindow getInstance(){
        if (null==window)
        {window=new CMessageWindow();}
        return window;
    }
/**
 * The core
 * @param sMessage
 * @param sType
 */
    private void updateMessages(final String sMessage, final String sType)

    {
        String sMessageHTML=""; 
        String sTypeText="";
        if (!sMessage.equals("\r\n")){ 
            sTypeText = sType+": ";
        }

        sMessageHTML = sMessage.replaceAll("(\r\n|\n)", "<br/>");
        if (!sMessageHTML.equals("<br/>")) 
        {
            sMessageHTML =   "<SPAN CLASS="+sType+">"+ sTypeText+sMessageHTML + "</SPAN>";
        }

        msgBuffer=msgBuffer.concat( sMessageHTML);
        editorPane.setText(msgBuffer);
        if ((editorPane.getDocument()).getLength()>1){
            editorPane.setCaretPosition((editorPane.getDocument()).getLength()-1);
        }  
    }

    public void setContainerFrame(JFrame jFrame){
        frameContainer = jFrame;
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(frameContainer.getContentPane());
        frameContainer.getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(scrollPane)
                );
        layout.setVerticalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(layout.createSequentialGroup()
                        .addComponent(scrollPane, javax.swing.GroupLayout.DEFAULT_SIZE, 217, Short.MAX_VALUE))
                );
    }

    public void setVisible(boolean bVisible){
        editorPane.setVisible(bVisible);
        scrollPane.setVisible(bVisible);
    }

    public void printMsg(String sMessage){
        String sType = MESSAGE;
        updateMessages(sMessage,sType);
    }

    public void printlnMsg(String sMessage){
        sMessage=sMessage.concat("\r\n");
        printMsg(sMessage);
    }

    public void printErr(String sMessage){
        String sType = ERROR;
        updateMessages(sMessage,sType);
    }

    public void printlnErr(String sMessage){
        sMessage=sMessage.concat("\r\n");
        printErr(sMessage);
    }

    public static void main(String args[]){
        CMessageWindow m_LogMgr;
        JFrame frame = new JFrame();
        m_LogMgr=CMessageWindow.getInstance();
        m_LogMgr.setContainerFrame(frame);
        frame.setVisible(true);
        frame.setSize(500, 500);

        for(int i=0;i<20;++i){
            m_LogMgr.printlnErr("MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM");
        }

        for(int i=0;i<150;++i){
            try {
                Thread.sleep(20);
            } catch (Exception e) {
            }
            m_LogMgr.printlnMsg("-----------------------");
        }

    }


}

Answer 1

You should not modify UI components outside the EDT.

If you add a call inside, say, your updateMessages so that the update happens on the EDT then the flicker goes away.

For example:

private void updateMessages(final String sMessage, final String sType)

{
    SwingUtilities.invokeLater( new Runnable() {
        public void run() {
            String sMessageHTML="";
            String sTypeText="";
            if (!sMessage.equals("\r\n")){
                sTypeText = sType+": ";
            }
            sMessageHTML = sMessage.replaceAll("(\r\n|\n)", "<br/>");
            if (!sMessageHTML.equals("<br/>"))
            {
                sMessageHTML =   "<SPAN CLASS="+sType+">"+ sTypeText+sMessageHTML + "</SPAN>";
            }

            msgBuffer=msgBuffer.concat( sMessageHTML);
            editorPane.setText(msgBuffer);
            if ((editorPane.getDocument()).getLength()>1){
                editorPane.setCaretPosition((editorPane.getDocument()).getLength()-1);
            }
        }
    });
}

Note that you shouldn’t perform long running operations on the EDT because otherwise you’ll “lock” your UI.