Java 为什么我会得到；值[null]无法转换为JRDataSource“；例外

我试图计算特定年份的入学人数

但是为什么我会得到这个例外（检查了一些现有的答案，但无法找出它。）

这是我的控制器

@RequestMapping(value ="/BMIbyage",method = RequestMethod.GET)
public ModelAndView BMIbyage(ModelAndView modelAndView, ModelMap model, Map<String, Object> map,HttpServletRequest request,
        @RequestParam("syear") int syear,@RequestParam("eyear") int eyear,HttpSession session){
    String childid = (String) session.getAttribute("childid");


    List<AdmissionSummery> asum = new ArrayList<AdmissionSummery>();

     List<PatientDetails> patientdetail = patientService.listpatient();

    for(int i=syear;i<=eyear;i++){
         asum.add(new AdmissionSummery());
        int no=0;
        for(int j=0;j<patientdetail.size();j++){


            float bmi = patientService.listPatient(patientdetail.get(j).getChildid()).get(0).getBmi();


            if(bmi<18.5){
                no=no+1;

                asum.get(asum.size()-1).setNooftime(no);

            }
            System.out.println("no"+no);
            System.out.println("j"+j);
            asum.get(asum.size()-1).setDuration(syear+" "+"-"+" "+eyear);
            asum.get(asum.size()-1).setYear(i);

            System.out.println("BMI"+bmi);

        }



        System.out.println("i"+i);
    }

      JRDataSource datasource = new JRBeanCollectionDataSource(asum);   

        model.addAttribute("datasourcebmireportA", datasource);

        model.addAttribute("format", "pdf");

        modelAndView = new ModelAndView("pdfReportViewaddsummeryA", model);



    return modelAndView;


}

@RequestMapping（value=“/BMIbyage”，method=RequestMethod.GET）
公共模型和视图BMIbyage（模型和视图模型和视图，模型映射模型，映射映射，HttpServletRequest请求，
@RequestParam（“syear”）int-syear，@RequestParam（“eyear”）int-eyear，HttpSession会话）{
String childid=（String）session.getAttribute（“childid”）；
列表

这是jasper-views.xml

<bean id="pdfReportViewaddsummeryA" class="org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView" p:url="/WEB-INF/Reports/BMIReport.jasper" p:reportDataKey="datasourceadmissionreportA" />

<bean id="pdfReportViewaddsummeryA" class="org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView" p:url="/WEB-INF/Reports/BMIReport.jasper" p:reportDataKey="datasourceadmissionreportA" />

---

更改jasper-views.xml时出现问题

<bean id="pdfReportViewaddsummeryA" class="org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView" p:url="/WEB-INF/Reports/BMIReport.jasper" p:reportDataKey="datasourcebmireportA" />

而不是

<bean id="pdfReportViewaddsummeryA" class="org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView" p:url="/WEB-INF/Reports/BMIReport.jasper" p:reportDataKey="datasourcebmireportA" />

<bean id="pdfReportViewaddsummeryA" class="org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView" p:url="/WEB-INF/Reports/BMIReport.jasper" p:reportDataKey="datasourceadmissionreportA" />