by doing following, we can only get the plain text form without html
tags, how to get HTML content from system clipboard with html tags?

Clipboard clipboard = Toolkit.getDefaultToolkit().getSystemClipboard();
Transferable contents = clipboard.getContents(null);
boolean hasTransferableText = (contents != null)
               &&
contents.isDataFlavorSupported(DataFlavor.stringFlavor);

There's no DataFlavor.HTML in DataFlavor class
static DataFlavor imageFlavor
static DataFlavor javaFileListFlavor
static DataFlavor plainTextFlavor
static DataFlavor stringFlavor
static String javaJVMLocalObjectMimeType
static String javaRemoteObjectMimeType
static String javaSerializedObjectMimeType