Ok, so here’s how it works; JasperFillManager actually returns a JasperPrint object, so:
// get the JRXML template as a stream
InputStream template = JasperReportsApplication.class
.getResourceAsStream("/sampleReport.xml");
// compile the report from the stream
JasperReport report = JasperCompileManager.compileReport(template);
// fill out the report into a print object, ready for export.
JasperPrint print = JasperFillManager.fillReport(report, new HashMap<String, String>());
// export it!
File pdf = File.createTempFile("output.", ".pdf");
JasperExportManager.exportReportToPdfStream(print, new FileOutputStream(pdf));
Enjoy.