把这段代码修改为多线程分批执行没20条分一批 if (ObjectUtil.isNotEmpty(pushMailboxList)) { pushMailboxList.stream().forEach(item -> { Township byId = townshipService.getById(item.getPushOrgid()); try { String email = byId.getEmail(); if (StrUtil.isNotBlank(email)) { String date = DateTime.now().toString(DatePattern.CHINESE_DATE_TIME_PATTERN); String content = "金平县气象局于" + date + "，发布了" + repProductContent.getReportName() + "气象服务通知，请您查收并注意做好防范工作。"; //发送邮件 MailUtil.send(email, repProductContent.getReportName(), content, false, FileUtil.file(filePath)); item.setIzEmailSuccess(1); pushMailboxList1.add(item); } else { item.setIzEmailSuccess(0); pushMailboxList1.add(item); } } catch (Exception e) { item.setIzEmailSuccess(0); pushMailboxList1.add(item); e.printStackTrace(); } }); }

如果要将上述代码修改为多线程分批执行每20条分一批，可以这样做：

1. 将原来的forEach循环替换为for循环，并设置循环变量i和每批数量batchSize（20）
2. 使用Java中的线程池创建一个线程池，并在循环中提交任务
3. 在任务中使用subList方法将原始数据分成每批数量的数据块
4. 等待所有任务完成

示例代码如下：

if (ObjectUtil.isNotEmpty(pushMailboxList)) {
    int batchSize = 20;
    int listSize = pushMailboxList.size();
    ExecutorService executor = Executors.newFixedThreadPool(5);
    for (int i = 0; i < listSize; i += batchSize) {
        List<PushMailbox> subList = pushMailboxList.subList(i, Math.min(i + batchSize, listSize));
        executor.submit(() -> {
            subList.stream().forEach(item -> {
                Township byId = townshipService.getById(item.getPushOrgid());
                try {
                    String email = byId.getEmail();
                    if (StrUtil.isNotBlank(email)) {
                        String date = DateTime.now().toString(DatePattern.CHINESE_DATE_TIME_PATTERN);
                        String content = "金平县气象局于" + date + "，发布了" + repProductContent.getReportName() + "气象服务通知，请您查收并注意做好防范工作。";
                        //发送邮件
                        MailUtil.send(email, repProductContent.getReportName(), content, false, FileUtil.file(filePath));
                        item.setIzEmailSuccess(1);
                        pushMailboxList1.add(item);
                    } else {
                        item.setIzEmailSuccess(0);
                        pushMailboxList1.add(item);
                    }
                } catch (Exception e) {
                    item.setIzEmailSuccess(0);
                    pushMailboxList1.add(item);
                    e.printStackTrace();
                }
            });
        });
    }
    executor.shutdown();
    try {