Retrieve Image from Model Element’s Description Using Open API

In Visual Paradigm every model elements and diagrams can be describe with rich text content. With Visual Paradigm’s Open API it provide a channel to user to manipulate the diagram and model elements. In this article we will show you how to retrieve the images inside model element’s rich text description for further manipulation. We will demonstrate this by putting the image into ImageIcon and display using a message pane.

Retrieve user selected elements in diagram

We first retrieve the model elements user selected in diagram.

// Retrieve the selected element in diagram
IDiagramElement[] selectedElements = ApplicationManager.instance().getDiagramManager().getActiveDiagram().getSelectedDiagramElement();

Retrieve the HTML description form selected model element

Once we got the selected model elements we can then process it one by one by getting its HTML description.

// Process the selected diagram one by one to retrieve its HTML description
// After that pass to retrieveImageFromElement method for processing,
// and append the images to collection 
for (IDiagramElement element : selectedElements) {
  String lDescription = element.getModelElement().getHTMLDescription();
  Collection<Image> descImage = retrieveImageFromElement(lDescription);
  if (descImage != null) {

Breakdown the HTML description

Next we put the HTML description into JEditorPane and using the built-in facilities to extract the HTML nodes for parsing.

Collection<Image> lImages = new ArrayList<Image>();
// Create JEditorPane to host the HTML description
JEditorPane p = new JEditorPane();

// Walk through the description and pass the HTML node 
// to recursive function parseImage to find out the image element
HTMLDocument d = (HTMLDocument) p.getDocument();
Element lRoot = d.getRootElements()[0];
int lCount = lRoot.getElementCount();
for (int i = 0; i < lCount; i++) {
  Element lElement = lRoot.getElement(i);				
  Object lElementNameAttribute = lElement.getAttributes().getAttribute(StyleConstants.NameAttribute);
  if (HTML.Tag.BODY == lElementNameAttribute) {
    parseImage(lElement, lImages);

Find out the image element from HTML content

After that we process the HTML nodes one by one to find out the image element.

int lElementCount = aParentElement.getElementCount();
for (int i = 0; i < lElementCount; i++) {
  Element lElement = aParentElement.getElement(i);
  Object lElementNameAttribute = lElement.getAttributes().getAttribute(StyleConstants.NameAttribute);
  // Local the image element
  if (HTML.Tag.IMG == lElementNameAttribute) {
    // Retrieve the source of the image
    Object lValue = lElement.getAttributes().getAttribute(HTML.Attribute.SRC);
    if (lValue instanceof String) {
      String lSrc = (String) lValue;
      if (lSrc.startsWith("Documentation/Clipboard/Images/")) {
        lSrc = lSrc.substring("Documentation/Clipboard/Images/".length());

Load the image into Image object

When image elements are found then we load it into java.awt.Image object.

// Read the image from file system and store it into Image object
try {
  InputStream lIs = ApplicationManager.instance().getViewManager().getDocumentationImageInputStream(lSrc);
  if (lIs != null) {
    try {
      Image lImage =;
      int lImageWidth = lImage.getWidth(null);
      int lImageHeight = lImage.getHeight(null);
      int lAvailableWidth = 100;
      int lAvailableHeight = 100;
      float lScale;
      if (lImageWidth > lAvailableWidth || lImageHeight > lAvailableHeight) {
        lScale = Math.min((lAvailableWidth/(float)lImageWidth), (lAvailableHeight/(float)lImageHeight));
        lImageWidth = (int) (lImageWidth*lScale);
        lImageHeight = (int) (lImageHeight*lScale);
      } else {
        lScale = 1f;
      if (lScale != 1f) {
        BufferedImage lImg = new BufferedImage(lImageWidth, lImageHeight, BufferedImage.TYPE_4BYTE_ABGR);
        Graphics2D lG = lImg.createGraphics();
        lG.drawImage(lImage, 0, 0, lImageWidth, lImageHeight, null);
        lImage = lImg;
      // Add the image into collection
    } finally {

Display the loaded image

Finally we put the image object into a panel and display it using message dialog.

// Create a panel for display the images as ImageIcon
// and show it with a Message Dialog
JPanel lPanel = new JPanel(new FlowLayout());
for (Image lImage : lImages) {
  JLabel lLabel = new JLabel(new ImageIcon(lImage));
ApplicationManager.instance().getViewManager().showMessageDialog(null, lPanel);

Sample Plugin

The sample plugin demonstrate how to load the image in model element’s description. After you deploy the plugin into Visual Paradigm you can then select the model element in diagram and click the plugin button in the application toolbar to trigger it.

Show the images inside selected model element's description

Show the images inside selected model element’s description

Download Sample Plugin

You can click this link to download the sample plugin.


Related Know-how

Related Link

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