In one of my previous posts, I had mentioned how to ignore pagination in excel reports. To achieve the same in HTML reports , we need to set the following parameters to the exporter before exporting.
htmlExporter.setParameter(JRHtmlExporterParameter.BETWEEN_PAGES_HTML, "");
htmlExporter.setParameter(JRHtmlExporterParameter.HTML_HEADER, "");
htmlExporter.setParameter(JRHtmlExporterParameter.HTML_FOOTER, "");
htmlExporter.setParameter(JRHtmlExporterParameter.IS_REMOVE_EMPTY_SPACE_BETWEEN_ROWS,
Boolean.TRUE);
For more details , you can refer to this page.