背景：由于查询接口调用第三方平台，需要通过http请求获得设备数据，但由于第三方接口获取数据的限制，只能通过某些接口获取机柜与机房、机柜与设备关系后再查询对应设备的信息，单线程执行效果慢造成了网络io耗时较长的问题，后引入CountDownLatch计数器来解决。

接口的响应时间

使用前：

 使用后：

上代码：

原来的代码（主要列出耗时代码块）：

@Override
    public Result searchDeviceList(HttpServletRequest httpRequest, DeviceQuery deviceQuery) {
        String cookie = httpRequest.getHeader("Cookie");

        List<DeviceQueryResponseVo> jsonList = new ArrayList<DeviceQueryResponseVo>();
        List<CabinetVo> cabinetVoList = new ArrayList<>();

        Map<String, CabinetVo> cabinetMap = new HashMap<>();
        Map<String, RoomCabinet> roomCabinetMap = new HashMap<>();
        Map<String, Object> result = new HashMap<>();
        try {
            //todo...

            if (cabinetCount > 0) {
                cabinetVoList = getCabinetList(cookie, CmdbConstants.CMDB_POST_CABINET_PAGE_URL, cabinetCount, cabinetVoList);

                for (int i = 0; i < cabinetVoList.size(); i++) {
                    String cabinetId = cabinetVoList.get(i).getBkInstId();
                    cabinetMap.put(cabinetId, cabinetVoList.get(i));
                    //查询机柜-机房
                    List<RoomVo> cabinetRoomVoList = new ArrayList<>();
                    cabinetRoomVoList = geRelationList(cookie, CmdbConstants.CMDB_POST_CABINET_DATA_CENTER_DEVICE_URL, cabinetRoomVoList, 1, Integer.parseInt(cabinetId));
                    String roomId = null;
                    if (CollectionUtils.isNotEmpty(cabinetRoomVoList)) {
                        roomId = cabinetRoomVoList.get(0).getBkInstId();
                    }
                    //查询机柜-设备
                    List<RoomVo> cabinetDeviceVoList = new ArrayList<>();
                    cabinetDeviceVoList = geRelationList(cookie, CmdbConstants.CMDB_POST_CABINET_DATA_CENTER_DEVICE_URL, cabinetDeviceVoList, 2, Integer.parseInt(cabinetId));
                    for (RoomVo roomVo : cabinetDeviceVoList) {
                        RoomCabinet roomCabinet = new RoomCabinet();
                        roomCabinet.setRoomId(roomId).setCabinetId(cabinetId);
                        roomCabinetMap.put(roomVo.getBkAsstInstId().toString(), roomCabinet);
                    }
                }
            } else {
                result.put("list", new ArrayList<DeviceQueryResponseVo>());
                result.put("total", 0);
                return Result.OK(result);
            }
            
	//todo...
            return Result.OK(result);
        } catch (InterruptedException e) {
            log.error("查询线程异常 ！");
            return Result.error(999, "查询失败,Cookie失效！");
        } catch (BaseException e) {
            return Result.error(999, e.getMsg());
        } catch (Exception e) {
            return Result.error(999, "查询失败,Cookie失效！");
        }
    }

使用CountDownLatch后，查询接口部分：

@Override
    public Result searchDeviceList(HttpServletRequest httpRequest, DeviceQuery deviceQuery) {
        String cookie = httpRequest.getHeader("Cookie");
      
        List<DeviceQueryResponseVo> jsonList = new ArrayList<DeviceQueryResponseVo>();
        List<CabinetVo> cabinetVoList = new ArrayList<>();

        Map<String, CabinetVo> cabinetMap = new HashMap<>();
        Map<String, RoomCabinet> roomCabinetMap = new HashMap<>();
        Map<String, Object> result = new HashMap<>();
        try {
          //todo...
            int cabinetCount = getCount(cookie, CmdbConstants.CMDB_POST_CABINET_COUNT_URL);
            CountDownLatch latch = new CountDownLatch(0);
            if (cabinetCount > 0) {
                cabinetVoList = getCabinetList(cookie, CmdbConstants.CMDB_POST_CABINET_PAGE_URL, cabinetCount, cabinetVoList);

                latch = new CountDownLatch(cabinetVoList.size());

                for (int i = 0; i < cabinetVoList.size(); i++) {
                    // 提交任务给线程池处理
                    executorConfig.asyncServiceExecutor().execute(new CabinetTask(cabinetVoList.get(i), cookie, cabinetMap, roomCabinetMap, latch,this));
                }
            } else {
                result.put("list", new ArrayList<DeviceQueryResponseVo>());
                result.put("total", 0);
                return Result.OK(result);
            }
            // 等待所有任务完成
            latch.await();
	//todo...
            return Result.OK(result);
        } catch (InterruptedException e) {
            log.error("查询线程异常 ！");
            return Result.error(999, "查询失败,Cookie失效！");
        } catch (BaseException e) {
            return Result.error(999, e.getMsg());
        } catch (Exception e) {
            return Result.error(999, "查询失败,Cookie失效！");
        }
    }

线程执行部分：

import com.baomidou.mybatisplus.core.toolkit.CollectionUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.CountDownLatch;

public class CabinetTask implements Runnable {
    private DeviceServiceImpl deviceService;
    private CabinetVo cabinetVo;
    private String cookie;
    private Map<String, CabinetVo> cabinetMap;
    private Map<String, RoomCabinet> roomCabinetMap;
    private CountDownLatch latch;

    public CabinetTask(CabinetVo cabinetVo, String cookie, Map<String, CabinetVo> cabinetMap,
                       Map<String, RoomCabinet> roomCabinetMap, CountDownLatch latch, DeviceServiceImpl deviceService) {
        this.cabinetVo = cabinetVo;
        this.cookie = cookie;
        this.cabinetMap = cabinetMap;
        this.roomCabinetMap = roomCabinetMap;
        this.latch = latch;
        this.deviceService = deviceService;
    }

    @Override
    public void run() {
        String cabinetId = cabinetVo.getBkInstId();
        cabinetMap.put(cabinetId, cabinetVo);

        //查询机柜-机房
        List<RoomVo> cabinetRoomVoList = new ArrayList<>();
        cabinetRoomVoList = deviceService.geRelationList(cookie, CmdbConstants.CMDB_POST_CABINET_DATA_CENTER_DEVICE_URL, cabinetRoomVoList, 1, Integer.parseInt(cabinetId));
        String roomId = null;
        if (CollectionUtils.isNotEmpty(cabinetRoomVoList)) {
            roomId = cabinetRoomVoList.get(0).getBkInstId();
        }

        //查询机柜-设备
        List<RoomVo> cabinetDeviceVoList = new ArrayList<>();
        cabinetDeviceVoList = deviceService.geRelationList(cookie, CmdbConstants.CMDB_POST_CABINET_DATA_CENTER_DEVICE_URL, new ArrayList<>(), 2, Integer.parseInt(cabinetVo.getBkInstId()));

        // 对 cabinetDeviceVoList 进行后续处理
        for (RoomVo roomVo : cabinetDeviceVoList) {
            RoomCabinet roomCabinet = new RoomCabinet();
            roomCabinet.setRoomId(roomId).setCabinetId(cabinetId);
            roomCabinetMap.put(roomVo.getBkAsstInstId().toString(), roomCabinet);
        }

        // 任务完成，减少任务计数
        latch.countDown();
    }
}