HTMLEditorKit editorKit = new HTMLEditorKit();
HTMLDocument document = (HTMLDocument) editorKit.createDefaultDocument();
JTextPane textPane = new JTextPane();
textPane.setContentType("text/html");
textPane.setDocument(document);

SimpleAttributeSet aSet = new SimpleAttributeSet();
StyleConstants.setLineSpacing(aSet, 50);
textPane.setParagraphAttributes(aSet, false);

document.setParagraphAttributes(0, document.getLength(), attr, replace);