public class StudentCount {

    private String grade;
    private  Long nums;

    public String getGrade() {
        return grade;
    }

    public void setGrade(String grade) {
        this.grade = grade;
    }

    public Long getNums() {
        return nums;
    }

    public void setNums(Long nums) {
        this.nums = nums;
    }
}

@GetMapping("/jasper4_chart")
    public void jasper4_chart( HttpServletResponse response)
            throws Exception {
        HashMap<String, Object> parameters = new HashMap<String, Object>();

        List<StudentCount> studentList = new ArrayList<>();
        for (int i = 1; i <= 6; i++) {
            Random random = new Random();
            int count = ((Double) (random.nextDouble() * 10)).intValue();
            StudentCount s1 = new StudentCount();
            s1.setGrade("grade"+ i );
            s1.setNums(i * 20L + count);
            studentList.add(s1);
        }
        String templatePath = "templates/template4_charts.jasper";
        JasperReportUtil.exportToPdf(templatePath, parameters, studentList, response);
    }