// 构建试卷对象。
 private Paper buildPaper(Subject subject, Area area) {
   Paper paper = new Paper();
   String examName = subject.getExam().getName();
   if (!StringUtils.isEmpty(examName) && !examName.endsWith("考试")) {
     examName = String.format("%s考试", examName);
   }
   paper.setName(
       String.format(
           "%1$s《%2$s》%3$s每日一练[%4$s]",
           examName,
           subject.getName(),
           (area == null ? "" : "[" + area.getName() + "]"),
           new SimpleDateFormat("yyyy-MM-dd").format(paper.getCreateTime())));
   paper.setSubject(subject);
   paper.setType(PaperType.DAILY.getValue());
   paper.setScore(null);
   paper.setTime(null);
   paper.setYear(Integer.parseInt(new SimpleDateFormat("yyyy").format(paper.getCreateTime())));
   paper.setArea(area);
   paper.setStructures(new TreeSet<Structure>());
   return paper;
 }