JasperPrintjasperPrint =  JasperFillManager.fillReport(filePath1, parameters1,jsource1);
JasperPrint jasperPrint2 =  JasperFillManager.fillReport(filePath2,parameters2, jsource2);


List jasperPrintList = new ArrayList();
jasperPrintList.add(jasperPrint);
jasperPrintList.add(jasperPrint2);


ByteArrayOutputStream baos = new ByteArrayOutputStream();(来源 www.iocblog.net)
              JRPdfExporter exporter = new JRPdfExporter();
              exporter.setParameter(JRExporterParameter.JASPER_PRINT_LIST,

jasperPrintList);
              exporter.setParameter(JRExporterParameter.OUTPUT_STREAM, baos);
              exporter.exportReport();
 byte[]   outputFile1=  baos.toByteArray();