背景
日常项目中，经常会出现一个场景，同时批量插入数据库数据，由于逻辑复杂或者其它原因，我们无法使用sql进行批量插入。串行效率低，耗时长，为了提高效率，这个时候我们首先想到多线程并发插入，但是如何控制事务呢 … 直接上干货
实现效果
开启多条子线程，并发插入数据库 当其中一条线程出现异常，或者处理结果为非预期结果，则全部线程均回滚
代码实现
@Service
public class CompanyUserBatchServiceImpl implements CompanyUserBatchService {
private static final Logger logger = LoggerFactory.getLogger(CompanyUserBatchServiceImpl.class);
@Autowired
private CompanyUserService companyUserService;
@Override
public ReturnData addNewCurrentCompanyUsers(String params) {
logger.info("addNewCompanyUsers 新增参保人方法");
logger.info(">>>>>>>>>>>>参数:{}", params);
ReturnData rd = new ReturnData();
rd.setRetCode(CommonConstants.RETURN_CODE_FAIL);
if (StringUtils.isBlank(params)) {
rd.setMsg("入参为空!");
logger.info(">>>>>>入参为空。");
return rd;
}
List<CompanyUserResultVo> companyUsers;
try {
companyUsers = JSONObject.parseArray(params, CompanyUserResultVo.class);
} catch (Exception e) {
logger.info(">>>>>>>>>入参格式有误: {}", e);
rd.setMsg("入参格式有误!");
return rd;
}
//每条线程最小处理任务数
int perThreadHandleCount = 1;
//线程池的最大线程数
int nThreads = 10;
int taskSize = companyUsers.size();
if (taskSize > nThreads * perThreadHandleCount) {
perThreadHandleCount = taskSize % nThreads == 0 ? taskSize / nThreads : taskSize / nThreads + 1;
nThreads = taskSize % perThreadHandleCount == 0 ? taskSize / perThreadHandleCount : taskSize / perThreadHandleCount + 1;
} else {
nThreads = taskSize;
}
logger.info("批量添加参保人taskSize: {}, perThreadHandleCount: {}, nThreads: {}", taskSize, perThreadHandleCount, nThreads);
CountDownLatch mainLatch = new CountDownLatch(1);
//监控子线程
CountDownLatch threadLatch = new CountDownLatch(nThreads);
//根据子线程执行结果判断是否需要回滚
BlockingDeque<Boolean> resultList = new LinkedBlockingDeque<>(nThreads);
//必须要使用对象，如果使用变量会造成线程之间不可共享变量值
RollBack rollBack = new RollBack(false);
ExecutorService fixedThreadPool = Executors.newFixedThreadPool(nThreads);
List<Future<List<Object>>> futures = Lists.newArrayList();
List<Object> returnDataList = Lists.newArrayList();
//给每个线程分配任务
for (int i = 0; i < nThreads; i++) {
int lastIndex = (i + 1) * perThreadHandleCount;
List<CompanyUserResultVo> companyUserResultVos = companyUsers.subList(i * perThreadHandleCount, lastIndex >= taskSize ? taskSize : lastIndex);
AddNewCompanyUserThread addNewCompanyUserThread = new AddNewCompanyUserThread(mainLatch, threadLatch, rollBack, resultList, companyUserResultVos);
Future<List<Object>> future = fixedThreadPool.submit(addNewCompanyUserThread);
futures.add(future);
}
/** 存放子线程返回结果. */
List<Boolean> backUpResult = Lists.newArrayList();
try {
//等待所有子线程执行完毕
boolean await = threadLatch.await(20, TimeUnit.SECONDS);
//如果超时，直接回滚
if (!await) {
rollBack.setRollBack(true);
} else {
logger.info("创建参保人子线程执行完毕，共 {} 个线程", nThreads);
//查看执行情况，如果有存在需要回滚的线程，则全部回滚
for (int i = 0; i < nThreads; i++) {
Boolean result = resultList.take();
backUpResult.add(result);
logger.debug("子线程返回结果result: {}", result);
if (result) {
/** 有线程执行异常，需要回滚子线程. */
rollBack.setRollBack(true);
}
}
}
} catch (InterruptedException e) {
logger.error("等待所有子线程执行完毕时，出现异常");
throw new SystemException("等待所有子线程执行完毕时，出现异常，整体回滚");
} finally {
//子线程再次开始执行
mainLatch.countDown();
logger.info("关闭线程池，释放资源");
fixedThreadPool.shutdown();
}
/** 检查子线程是否有异常，有异常整体回滚. */
for (int i = 0; i < nThreads; i++) {
if (CollectionUtils.isNotEmpty(backUpResult)) {
Boolean result = backUpResult.get(i);
if (result) {
logger.info("创建参保人失败，整体回滚");
throw new SystemException("创建参保人失败");
}
} else {
logger.info("创建参保人失败，整体回滚");
throw new SystemException("创建参保人失败");
}
}
//拼接结果
try {
for (Future<List<Object>> future : futures) {
returnDataList.addAll(future.get());
}
} catch (Exception e) {
logger.info("获取子线程操作结果出现异常,创建的参保人列表： {} ，异常信息： {}", JSONObject.toJSONString(companyUsers), e);
throw new SystemException("创建参保人子线程正常创建参保人成功，主线程出现异常，回滚失败");
}
rd.setRetCode(CommonConstants.RETURN_CODE_SUCCESS);
rd.setData(returnDataList);
return rd;
}
public class AddNewCompanyUserThread implements Callable<List<Object>> {
/**
* 主线程监控
*/
private CountDownLatch mainLatch;
/**
* 子线程监控
*/
private CountDownLatch threadLatch;
/**
* 是否回滚
*/
private RollBack rollBack;
private BlockingDeque<Boolean> resultList;
private List<CompanyUserResultVo> taskList;
public AddNewCompanyUserThread(CountDownLatch mainLatch, CountDownLatch threadLatch, RollBack rollBack, BlockingDeque<Boolean> resultList, List<CompanyUserResultVo> taskList) {
this.mainLatch = mainLatch;
this.threadLatch = threadLatch;
this.rollBack = rollBack;
this.resultList = resultList;
this.taskList = taskList;
}
@Override
public List<Object> call() {
//为了保证事务不提交，此处只能调用一个有事务的方法，spring 中事务的颗粒度是方法，只有方法不退出，事务才不会提交
return companyUserService.addNewCompanyUsers(mainLatch, threadLatch, rollBack, resultList, taskList);
}
}
public class RollBack {
private Boolean isRollBack;
public Boolean getRollBack() {
return isRollBack;
}
public void setRollBack(Boolean rollBack) {
isRollBack = rollBack;
}
public RollBack(Boolean isRollBack) {
this.isRollBack = isRollBack;
}
}
public List<Object> addNewCompanyUsers(CountDownLatch mainLatch, CountDownLatch threadLatch, CompanyUserBatchServiceImpl.RollBack rollBack, BlockingDeque<Boolean> resultList, List<CompanyUserResultVo> taskList) {
List<Object> returnDataList = Lists.newArrayList();
Boolean result = false;
logger.debug("线程: {}创建参保人条数 : {}", Thread.currentThread().getName(), taskList.size());
try {
for (CompanyUserResultVo companyUserResultVo : taskList) {
ReturnData returnData = addSingleCompanyUser(companyUserResultVo);
if (returnData.getRetCode() == CommonConstants.RETURN_CODE_FAIL) {
result = true;
}
returnDataList.add(returnData.getData());
}
//Exception 和 Error 都需要抓
} catch (Throwable throwable) {
throwable.printStackTrace();
logger.info("线程: {}创建参保人出现异常： {} ", Thread.currentThread().getName(), throwable);
result = true;
}
resultList.add(result);
threadLatch.countDown();
logger.info("子线程 {} 计算过程已经结束，等待主线程通知是否需要回滚", Thread.currentThread().getName());
try {
mainLatch.await();
logger.info("子线程 {} 再次启动", Thread.currentThread().getName());
} catch (InterruptedException e) {
logger.error("批量创建参保人线程InterruptedException异常");
throw new SystemException("批量创建参保人线程InterruptedException异常");
}
if (rollBack.getRollBack()) {
logger.error("批量创建参保人线程回滚, 线程: {}, 需要更新的信息taskList: {}",
Thread.currentThread().getName(),
JSONObject.toJSONString(taskList));
logger.info("子线程 {} 执行完毕，线程退出", Thread.currentThread().getName());
throw new SystemException("批量创建参保人线程回滚");
}
logger.info("子线程 {} 执行完毕，线程退出", Thread.currentThread().getName());
return returnDataList;
}
思想就是使用两个CountDownWatch实现子线程的二段提交
步骤：
主线程将任务分发给子线程，然后 使用 boolean await = threadLatch.await(20, TimeUnit.SECONDS); 阻塞主线程，等待所有子线程处理向数据库中插入的业务 使用 threadLatch.countDown(); 释放子线程锁定，同时使用 mainLatch.await(); 阻塞子线程，将程序的控制权交还给主线程 主线程检查子线程执行插入数据库的结果，若有非预期结果出现，主线程标记状态告知子线程回滚，然后使用 mainLatch.countDown(); 将程序控制权再次交给子线程，子线程检测回滚标志，判断是否回滚 子线程执行结束，主线程拼接处理结果，响应给请求方
整个过程类似于GC的标记-清除过程（串行的垃圾收集器）
