How to change the color of specific words in a JTextPane?

Question

How do I change the color of specific words in a JTextPane just while the user is typing? Should I override JTextPane paintComponent m

Answer 1

Another solution is to use a DocumentFilter.

Here is an example:

Create a class that extends DocumentFilter:

private final class CustomDocumentFilter extends DocumentFilter
{
        private final StyledDocument styledDocument = yourTextPane.getStyledDocument();

        private final StyleContext styleContext = StyleContext.getDefaultStyleContext();
        private final AttributeSet greenAttributeSet = styleContext.addAttribute(styleContext.getEmptySet(), StyleConstants.Foreground, Color.GREEN);
        private final AttributeSet blackAttributeSet = styleContext.addAttribute(styleContext.getEmptySet(), StyleConstants.Foreground, Color.BLACK);

    // Use a regular expression to find the words you are looking for
    Pattern pattern = buildPattern();

    @Override
    public void insertString(FilterBypass fb, int offset, String text, AttributeSet attributeSet) throws BadLocationException {
        super.insertString(fb, offset, text, attributeSet);

        handleTextChanged();
    }

    @Override
    public void remove(FilterBypass fb, int offset, int length) throws BadLocationException {
        super.remove(fb, offset, length);

        handleTextChanged();
    }

    @Override
    public void replace(FilterBypass fb, int offset, int length, String text, AttributeSet attributeSet) throws BadLocationException {
        super.replace(fb, offset, length, text, attributeSet);

        handleTextChanged();
    }

    /**
     * Runs your updates later, not during the event notification.
     */
    private void handleTextChanged()
    {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                updateTextStyles();
            }
        });
    }

    /**
     * Build the regular expression that looks for the whole word of each word that you wish to find.  The "\\b" is the beginning or end of a word boundary.  The "|" is a regex "or" operator.
     * @return
     */
    private Pattern buildPattern()
    {
        StringBuilder sb = new StringBuilder();
        for (String token : ALL_WORDS_THAT_YOU_WANT_TO_FIND) {
            sb.append("\\b"); // Start of word boundary
            sb.append(token);
            sb.append("\\b|"); // End of word boundary and an or for the next word
        }
        if (sb.length() > 0) {
            sb.deleteCharAt(sb.length() - 1); // Remove the trailing "|"
        }

        Pattern p = Pattern.compile(sb.toString());

        return p;
    }


    private void updateTextStyles()
    {
        // Clear existing styles
        styledDocument.setCharacterAttributes(0, yourTextPane.getText().length(), blackAttributeSet, true);

        // Look for tokens and highlight them
        Matcher matcher = pattern.matcher(yourTextPane.getText());
        while (matcher.find()) {
            // Change the color of recognized tokens
            styledDocument.setCharacterAttributes(matcher.start(), matcher.end() - matcher.start(), greenAttributeSet, false);
        }
    }
}

All you need to do then is apply the DocumentFilter that you created to your JTextPane as follows:

((AbstractDocument) yourTextPane.getDocument()).setDocumentFilter(new CustomDocumentFilter());