java多次嵌套循环查询数据库导致代码中数据处理慢如何解决

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业务现象

代码中有一部分代码多次嵌套循环和数据处理，执行速度很慢

解决方案

通过多线程

1、启用多线程

private final static Executor executor = Executors.newFixedThreadPool(3);

2、初始化设置count

即等待(await)count个线程或一个线程count次计数，通过工作线程来countDown计数减一，直到计数为0，await阻塞结束；目的：保证所有线程都走完  

final CountDownLatch latch = new CountDownLatch(dataList.size());

3、需要重新run

需要多线程的代码写在run中

 @Override
       public void run() { 

                //业务代码处理

                //countDown计数减一

                 latch.countDown();

}

4、阻塞线程

  // 等待所有工作线程结束
            latch.await();

关键代码

 private final static Executor executor = Executors.newFixedThreadPool(3);//启用多线程
 
 public Result getList(@RequestBody StatusDbSelectParam param){
 
PageHelper.startPage(param.getPageNum(), param.getPageSize());
        List<Map<String, Object>> dataList = statusDbService.selectByTime(tableName,             columnNames.toString(), param.getStartTime(), param.getEndTime());
        //初始化设置count，即等待(await)count个线程或一个线程count次计数，通过工作线程来countDown计数减一，直到计数为0，await阻塞结束
        final CountDownLatch latch = new CountDownLatch(dataList.size());
        for(int k =0;k<dataList.size();k++) {
            final int i = k;
            String finalTableName = tableName;
            executor.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        Map<String, Object> map = dataList.get(i);
                        for (String pid : map.keySet()) {
                            String val = String.valueOf(map.get(pid));
                            String columPid = pid.substring(2, pid.length()).toLowerCase();
                            List<MonitorRuleEntity> list = monitorRuleService.listMonitorRule(columPid, finalTableName);
                            String status = "";
                            //循环规则数据 判断监测点是否报警 更新状态
                            for (int j = 0; j < list.size(); j++) {
                                Boolean flag = DevHealthStatusFactory.getInstance().getResultMapByRule(val, list.get(j));
                                if (flag) {
                                    if (j == 0) {
                                        status = "A";
                                        break;
                                    } else if (j == 1) {
                                        status = "B";
                                        break;
                                    } else if (j == 2) {
                                        status = "C";
                                        break;
                                    }
                                }
                            }
                            if (pid.equalsIgnoreCase(timeColumnName)) {
                                map.put(pid, val);
                            } else {
                                map.put(pid, val + "_" + status);
                            }
                        }
                        latch.countDown();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            });
        }
        try {
            // 等待所有工作线程结束
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return ResultMsg.successMsg().data(new PageInfo<>(dataList));
    }