Java多线程批量拆分List导入数据库-技术圈

# 前言

前两天做了一个导入的功能，导入开始的时候非常慢，导入2w条数据要1分多钟，后来一点一点的优化，从直接把list怼进Mysql中，到分配把list导入Mysql中，到多线程把list导入Mysql中。时间是一点一点的变少了。非常的爽，最后变成了10s以内。下面就展示一下过程。

# 直接把list怼进Mysql

使用mybatis的批量导入操作：

  @Transactional(rollbackFor = Exception.class)    public int addFreshStudentsNew2(List list, String schoolNo) {        if (list == null || list.isEmpty()) {            return 0;        }        List studentEntityList = new LinkedList<>();        List enrollStudentEntityList = new LinkedList<>();        List allusersEntityList = new LinkedList<>();

        for (FreshStudentAndStudentModel freshStudentAndStudentModel : list) {

            EnrollStudentEntity enrollStudentEntity = new EnrollStudentEntity();            StudentEntity studentEntity = new StudentEntity();            BeanUtils.copyProperties(freshStudentAndStudentModel, studentEntity);            BeanUtils.copyProperties(freshStudentAndStudentModel, enrollStudentEntity);            String operator = TenancyContext.UserID.get();            String studentId = BaseUuidUtils.base58Uuid();            enrollStudentEntity.setId(BaseUuidUtils.base58Uuid());            enrollStudentEntity.setStudentId(studentId);            enrollStudentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            enrollStudentEntity.setOperator(operator);            studentEntity.setId(studentId);            studentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            studentEntity.setOperator(operator);            studentEntityList.add(studentEntity);            enrollStudentEntityList.add(enrollStudentEntity);

            AllusersEntity allusersEntity = new AllusersEntity();            allusersEntity.setId(enrollStudentEntity.getId());            allusersEntity.setUserCode(enrollStudentEntity.getNemtCode());            allusersEntity.setUserName(enrollStudentEntity.getName());            allusersEntity.setSchoolNo(schoolNo);            allusersEntity.setTelNum(enrollStudentEntity.getTelNum());            allusersEntity.setPassword(enrollStudentEntity.getNemtCode());  //密码设置为考生号            allusersEntityList.add(allusersEntity);        }            enResult = enrollStudentDao.insertAll(enrollStudentEntityList);            stuResult = studentDao.insertAll(studentEntityList);            allResult = allusersFacade.insertUserList(allusersEntityList);

        if (enResult > 0 && stuResult > 0 && allResult) {            return 10;        }        return -10;    }

Mapper.xml

代码说明：

          insert into tb_enroll_student                        id,                  remark,                  nEMT_aspiration,                  nEMT_code,                  nEMT_score,                  student_id,                  identity_card_id,                  level,                  major,                  name,                  nation,                  secondary_college,                  operator,                  sex,                  is_delete,                  account_address,                  native_place,                  original_place,                  used_name,                  pictrue,                  join_party_date,                  political_status,                  tel_num,                  is_registry,                  graduate_school,                  create_time,                  update_time                        values                (                #{item.id,jdbcType=VARCHAR},                #{item.remark,jdbcType=VARCHAR},                #{item.nemtAspiration,jdbcType=VARCHAR},                #{item.nemtCode,jdbcType=VARCHAR},                #{item.nemtScore,jdbcType=VARCHAR},                #{item.studentId,jdbcType=VARCHAR},                #{item.identityCardId,jdbcType=VARCHAR},                #{item.level,jdbcType=VARCHAR},                #{item.major,jdbcType=VARCHAR},                #{item.name,jdbcType=VARCHAR},                #{item.nation,jdbcType=VARCHAR},                #{item.secondaryCollege,jdbcType=VARCHAR},                #{item.operator,jdbcType=VARCHAR},                #{item.sex,jdbcType=VARCHAR},                0,                #{item.accountAddress,jdbcType=VARCHAR},                #{item.nativePlace,jdbcType=VARCHAR},                #{item.originalPlace,jdbcType=VARCHAR},                #{item.usedName,jdbcType=VARCHAR},                #{item.pictrue,jdbcType=VARCHAR},                #{item.joinPartyDate,jdbcType=VARCHAR},                #{item.politicalStatus,jdbcType=VARCHAR},                #{item.telNum,jdbcType=VARCHAR},                #{item.isRegistry,jdbcType=TINYINT},                #{item.graduateSchool,jdbcType=VARCHAR},                now(),                now()                )

底层的mapper是通过逆向工程来生成的，批量插入如下，是拼接成类似：insert into tb_enroll_student（）values （），（）…….（）；

这样的缺点是，数据库一般有一个默认的设置，就是每次sql操作的数据不能超过4M。这样插入，数据多的时候，数据库会报错Packet for query is too large (6071393 > 4194304). You can change this value on the server by setting the max_allowed_packet' variable.，虽然我们可以通过

类似修改 my.ini 加上 max_allowed_packet =67108864，67108864=64M，默认大小4194304 也就是4M

修改完成之后要重启mysql服务，如果通过命令行修改就不用重启mysql服务。

完成本次操作，但是我们不能保证项目单次最大的大小是多少，这样是有弊端的。所以可以考虑进行分组导入。

# 分组把list导入Mysql中

同样适用mybatis批量插入，区别是对每次的导入进行分组计算，然后分多次进行导入：

代码说明：

 @Transactional(rollbackFor = Exception.class)    public int addFreshStudentsNew2(List list, String schoolNo) {        if (list == null || list.isEmpty()) {            return 0;        }        List studentEntityList = new LinkedList<>();        List enrollStudentEntityList = new LinkedList<>();        List allusersEntityList = new LinkedList<>();

        for (FreshStudentAndStudentModel freshStudentAndStudentModel : list) {

            EnrollStudentEntity enrollStudentEntity = new EnrollStudentEntity();            StudentEntity studentEntity = new StudentEntity();            BeanUtils.copyProperties(freshStudentAndStudentModel, studentEntity);            BeanUtils.copyProperties(freshStudentAndStudentModel, enrollStudentEntity);            String operator = TenancyContext.UserID.get();            String studentId = BaseUuidUtils.base58Uuid();            enrollStudentEntity.setId(BaseUuidUtils.base58Uuid());            enrollStudentEntity.setStudentId(studentId);            enrollStudentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            enrollStudentEntity.setOperator(operator);            studentEntity.setId(studentId);            studentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            studentEntity.setOperator(operator);            studentEntityList.add(studentEntity);            enrollStudentEntityList.add(enrollStudentEntity);

            AllusersEntity allusersEntity = new AllusersEntity();            allusersEntity.setId(enrollStudentEntity.getId());            allusersEntity.setUserCode(enrollStudentEntity.getNemtCode());            allusersEntity.setUserName(enrollStudentEntity.getName());            allusersEntity.setSchoolNo(schoolNo);            allusersEntity.setTelNum(enrollStudentEntity.getTelNum());            allusersEntity.setPassword(enrollStudentEntity.getNemtCode());  //密码设置为考生号            allusersEntityList.add(allusersEntity);        }

        int c = 100;        int b = enrollStudentEntityList.size() / c;        int d = enrollStudentEntityList.size() % c;

        int enResult = 0;        int stuResult = 0;        boolean allResult = false;

        for (int e = c; e <= c * b; e = e + c) {            enResult = enrollStudentDao.insertAll(enrollStudentEntityList.subList(e - c, e));            stuResult = studentDao.insertAll(studentEntityList.subList(e - c, e));            allResult = allusersFacade.insertUserList(allusersEntityList.subList(e - c, e));        }        if (d != 0) {            enResult = enrollStudentDao.insertAll(enrollStudentEntityList.subList(c * b, enrollStudentEntityList.size()));            stuResult = studentDao.insertAll(studentEntityList.subList(c * b, studentEntityList.size()));            allResult = allusersFacade.insertUserList(allusersEntityList.subList(c * b, allusersEntityList.size()));        }

        if (enResult > 0 && stuResult > 0 && allResult) {            return 10;        }        return -10;    }

这样操作，可以避免上面的错误，但是分多次插入，无形中就增加了操作实践，很容易超时。所以这种方法还是不值得提倡的。

再次改进，使用多线程分批导入。

# 多线程分批导入Mysql

依然使用mybatis的批量导入，不同的是，根据线程数目进行分组，然后再建立多线程池，进行导入。

代码说明：

  @Transactional(rollbackFor = Exception.class)    public int addFreshStudentsNew(List list, String schoolNo) {        if (list == null || list.isEmpty()) {            return 0;        }        List studentEntityList = new LinkedList<>();        List enrollStudentEntityList = new LinkedList<>();        List allusersEntityList = new LinkedList<>();

        list.forEach(freshStudentAndStudentModel -> {            EnrollStudentEntity enrollStudentEntity = new EnrollStudentEntity();            StudentEntity studentEntity = new StudentEntity();            BeanUtils.copyProperties(freshStudentAndStudentModel, studentEntity);            BeanUtils.copyProperties(freshStudentAndStudentModel, enrollStudentEntity);            String operator = TenancyContext.UserID.get();            String studentId = BaseUuidUtils.base58Uuid();            enrollStudentEntity.setId(BaseUuidUtils.base58Uuid());            enrollStudentEntity.setStudentId(studentId);            enrollStudentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            enrollStudentEntity.setOperator(operator);            studentEntity.setId(studentId);            studentEntity.setIdentityCardId(freshStudentAndStudentModel.getIdCard());            studentEntity.setOperator(operator);            studentEntityList.add(studentEntity);            enrollStudentEntityList.add(enrollStudentEntity);

            AllusersEntity allusersEntity = new AllusersEntity();            allusersEntity.setId(enrollStudentEntity.getId());            allusersEntity.setUserCode(enrollStudentEntity.getNemtCode());            allusersEntity.setUserName(enrollStudentEntity.getName());            allusersEntity.setSchoolNo(schoolNo);            allusersEntity.setTelNum(enrollStudentEntity.getTelNum());            allusersEntity.setPassword(enrollStudentEntity.getNemtCode());  //密码设置为考生号            allusersEntityList.add(allusersEntity);        });



        int nThreads = 50;

        int size = enrollStudentEntityList.size();        ExecutorService executorService = Executors.newFixedThreadPool(nThreads);        List> futures = new ArrayList>(nThreads);

        for (int i = 0; i < nThreads; i++) {            final List EnrollStudentEntityImputList = enrollStudentEntityList.subList(size / nThreads * i, size / nThreads * (i + 1));            final List studentEntityImportList = studentEntityList.subList(size / nThreads * i, size / nThreads * (i + 1));            final List allusersEntityImportList = allusersEntityList.subList(size / nThreads * i, size / nThreads * (i + 1));

           Callable task1 = () -> {          studentSave.saveStudent(EnrollStudentEntityImputList,studentEntityImportList,allusersEntityImportList);               return 1;            };          futures.add(executorService.submit(task1));        }        executorService.shutdown();        if (!futures.isEmpty() && futures != null) {            return 10;        }        return -10;    }

上面是通过应用ExecutorService 建立了固定的线程数，然后根据线程数目进行分组，批量依次导入。一方面可以缓解数据库的压力，另一个面线程数目多了，一定程度会提高程序运行的时间。缺点就是要看服务器的配置，如果配置好的话就可以开多点线程，配置差的话就开小点。

# 小结

通过使用这个操作真是不断的提高了，项目使用技巧也是不错。加油~~ 多线程哦