java使用iText导出pdf添加页眉，并设置图片

	PdfWriter pdfWriter;
	Document document;

	 
	public ExportPDF(File file) {
		document = new Document();// 建立一个Document对象
		document.setPageSize(PageSize.A4);// 设置页面大小

		try {

			pdfWriter = PdfWriter.getInstance(document, new FileOutputStream(file));

			document.open();

		} catch (Exception e) {

			e.printStackTrace();

		}
	}

	// 页眉事件
	private static class Header extends PdfPageEventHelper {
		public static PdfPTable header;

		public Header(PdfPTable header) {
			Header.header = header;
		}

		@Override
		public void onEndPage(PdfWriter writer, Document document) {
			// 把页眉表格定位
			header.writeSelectedRows(0, -1, 30, 806, writer.getDirectContent());
		}

		/**
		 * 设置页眉
		 * 
		 * @param writer
		 * @param req
		 * @throws Exception 
		 */
		public void setTableHeader(PdfWriter writer) throws Exception {
	        String realPath = ServletContextFactory.getServletContext().getRealPath(