How to copy text with style from a JavaFX text area?

Look at how the JavaFX Clipboard works.

Here is an example from the Javadoc of putting both plain text and formatted text in the clipboard:

final Clipboard clipboard = Clipboard.getSystemClipboard();
final ClipboardContent content = new ClipboardContent();
content.putString("Some text");
content.putHtml("<b>Some</b> text");
clipboard.setContent(content);

Specially, look at the standard DataFormats, which are FILES, HTML, IMAGE, PLAIN_TEXT, RTF and URL.

If you want to include formatting information in the ClipboardContent, then you need to use a data format that allows formatted data AND you need to include the formatting information in the data.

Examples of data formats which support text formatting are HTML and RTF. You can use standard data formats or you can create your own.

A TextArea does not work with formatted text. The text area itself can be styled, but the text in it will just follow the style of the text area when displayed. When you copy text out of the text area it will not be formatted, it will just be PLAIN_TEXT which is placed in the clipboard.

If you wanted to format the content when it was copied out of a text area then you would need to intercept or override the default copy function coded in the JavaFX system for the text area. When the text area adds the copied text to the clipboard, instead of adding plain text, add formatted text with appropriate formatting that you apply. This is probably possible, though non-trivial and I'm not currently going to try to write code to do this here (another motivated answerer could do so in another answer if they wished).

Rather than working with the JavaFX TextArea, which isn't built to deal with rich formatted text, you could work with a different kind of text editor which is built to deal with such formatted text.

Examples are:

1. The 3rd party RichTextFx project.
2. A JavaScript HTML based rich text editor displayed in a WebView
3. The in-built JavaFX HTMLEditor.

If you copy formatted text out of these controls which have been designed to work with formatted text, then, unlike the text editor which is designed to work with plain text, information should be copied to the clipboard using a format style and formatted data (e.g. a HTML data format for the clipboard content of data copied from the HTML based options I outlined earlier). I only say should be here because, the actual format used will depend on the implementation.

But, even if you manage to get formatted data into the clipboard, that is only half of the problem. When somebody takes the clipboard content and pastes it somewhere, the consuming application needs to understand both the data format and the data inside it in order to make use of it. So, if you just made up your own data format, unless you also wrote and controlled the application which consumes the pasted data, nothing would be able to make use of it. Instead you need to understand which data formats the consuming application understand, and use those. That way the consuming application will be able to decode, process and, if necessary, display the pasted data.

For examples on Clipboard usage for creating and consuming clipboard content in JavaFX programs, see the Oracle tutorials and examples for clipboard and drag operations, which are very good, though not comprehensive.