JsonDataSource for table fields get empty Jasper report

Question

I am new to jasper reports. I am trying to generate a pdf from a son file, which contains some info like name, class etc and an array marks. I am trying to render the marks array as a table. my JSON is

{"data": {"name" : "Johny",
    "class" : "A2",
    "sub" : "cs",
    "interest" : "films",
    "marks" : [{
               "subject" : "Maths",
               "mark" : "24",
               "grade" : "A",
               "remarks" : "",
               "slNo" : "1"
               },
               {
               "subject" : "English",
               "mark" : "24",
               "grade" : "A",
               "remarks" : "",
               "slNo" : "2"
               },

               ]
}}

I have given subdatasource expression as

<dataSourceExpression><![CDATA[((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource()]]></dataSourceExpression>

Full jrxml - Here

Now I call these from java like,

File jsonFile = new File("/Volumes/Johny/Work/EclipseWorkspace/SecondReport/res/Marks.Json");
JasperDesign jasperDesign = JRXmlLoader.load(new File("/Volumes/Johny/Work/EclipseWorkspace/SecondReport/res/First.jrxml"));
JasperReport jasperReport = JasperCompileManager.compileReport(jasperDesign);

parameters.put(JsonQueryExecuterFactory.JSON_INPUT_STREAM, new FileInputStream(jsonFile));
JasperPrint jasperPrint = JasperFillManager.fillReport(jasperReport, parameters);
JasperExportManager.exportReportToPdfFile(jasperPrint, "/Users/johnykutty/Desktop/Sample2.pdf");

Other fields are getting populated, but table values are getting as null.

Answer 1

Found answer from here The issue was I have to pass the key for the array in dataSourceExpression. So, the dataSourceExpression should be like

<dataSourceExpression><![CDATA[((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource("marks")]]></dataSourceExpression>

Note the "marks" parameter to subDataSource() method