ServiceImpl层：

public List<SchoolTask> exportAll(HttpServletRequest request) throws Exception{
         List<String> list = indexDao.findKemu();
         List<SchoolTask> listA = indexDao.findAll();//查找全部实体属性字段
         List<String> questionName = indexDao.selectSubjectName(list);
         List<SchoolTask> addList = new ArrayList<>();
         Map<String, List<SchoolTask>> maps = new HashMap<String, List<SchoolTask>>();
         String subjectName = listA.get(0).getSubjectName();
         for (int x = 0; x < listA.size(); x++) {
             if (!listA.get(x).getSubjectName().equals(subjectName)) {
                 maps.put(subjectName, addList);
                 subjectName = listA.get(x).getSubjectName();
                 addList = new ArrayList<>();
             }
             addList.add(listA.get(x));
             if (x == listA.size() - 1) {
                 maps.put(subjectName, addList);
             }
         }
         
         
         ExecutorService pool = Executors.newSingleThreadExecutor();//创建线程池
         CountDownLatch doneSignal = new CountDownLatch(list.size());//线程计数器
         for(int x=0;x<list.size();x++) {
             pool.submit(new ExcelRunnable(doneSignal,list.get(x)+".xlsx",maps.get(list.get(x)),questionName));
         }
         doneSignal.await();
         pool.shutdown();
         
         return listA;
     }

util：

public class ExcelRunnable implements Runnable {
    private final CountDownLatch doneSignal;
    private List<SchoolTask> listA;
     
     private List<String> questionName;    private String excelName;
     public ExcelRunnable(CountDownLatch doneSignal, String excelName, List<SchoolTask> listA, List<String> questionName) {
         this.doneSignal = doneSignal;
         this.listA = listA;
         this.questionName=questionName;
         this.excelName=excelName;
     }     @Override
     public void run() {
         System.out.println(Thread.currentThread().getName());
         String[] excelHeader = new String[questionName.size() + 1];
         excelHeader[0] = "学校";
         int add = 1;
         for (String qn : questionName) {
             excelHeader[add] = qn;
             add++;
         }
         XSSFWorkbook hwb = null;        try {
             hwb = creatExcel(listA, excelHeader);
         } catch (Exception e) {
             e.printStackTrace();
         }
         FileOutputStream fos=null;
         try {
             fos = new FileOutputStream("E://"+excelName);
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         }
         try {
             hwb.write(fos);// 写入
             fos.close();// 关闭资源
         } catch (IOException e) {
             e.printStackTrace();
         }finally {
             doneSignal.countDown();//线程-1
         }
         
     }    private XSSFWorkbook creatExcel(List<SchoolTask> listA,String[] excelHeader) throws Exception {
         XSSFWorkbook hwb = new XSSFWorkbook();// 第一步，创建一个workbook（一个excel文件）
         XSSFSheet hs = hwb.createSheet("表格详情信息");// 第二步，在workbook中添加一个sheet，对应excel文件中sheet
         XSSFRow hr = hs.createRow((int) 0);// 第三部，在sheet中添加表头第0行（相当于解释字段）
         XSSFCellStyle hcs = hwb.createCellStyle();// 第四步，设置第0行（表头）居中
         hcs.setAlignment(XSSFCellStyle.ALIGN_CENTER);// 创建居中格式
         // 将表头的字段放入数组当中
         for (int i = 0; i < excelHeader.length; i++) {
             XSSFCell cell = hr.createCell(i);// 顺序创建
             cell.setCellValue(excelHeader[i]);// 顺序塞入
             cell.setCellStyle(hcs);// 居中
             hs.autoSizeColumn(i);// 设置 i这一列为自动调整列宽
         }
         
         String sname="";
         int j=1;
         int ce=0;
         XSSFRow xr = null;
         for(int x=0;x<listA.size();x++) {
             if(!listA.get(x).getSchoolName().equals(sname)) {
                 xr = hs.createRow(j);
                 xr.createCell(0).setCellValue(listA.get(x).getSchoolName());
                 sname = listA.get(x).getSchoolName();
                 j++;
                 ce=0;
             }
             ce++;
             xr.createCell(ce).setCellValue(listA.get(x).getTask());
         }
         return hwb;
     }}