String file = (String) request.getParameter("file");
FileInputStream is = new FileInputStream(new File(file););
ReportJob job = new ReportJob(is);
job.setParameter("mymonth",request.getParameter("mymonth")) // 把参数传到报表引擎里去
// 输出报表到response上
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
job.printAsDHTML(ff, out);
具体你可以参照 JatoolsReportServlet, ReportWriter 两个类.