Java应用诊断利器-Arthus

2023-02-12

字数统计: 2.8k字 | 阅读时长≈ 15分

前言

大家是否碰到线上环境日志打印不全，系统业务逻辑复杂方法嵌套深排查错误和定位优化耗时问题困难，那么阿里开源的 Java 诊断工具Arthus能很好的帮助我们查看方法调用的出入参、异常，监测方法执行耗时，类加载信息等，大大提升线上问题排查效率。

1.安装Arthas

下载arthas-boot.jar：

1	curl -O https://arthas.aliyun.com/arthas-boot.jar

2.启动Arthas

用java -jar的方式启动,并选择自己启动的java程序：

yinshuang$ java -jar arthas-boot.jar
[INFO] arthas-boot version: 3.6.3
[INFO] Found existing java process, please choose one and input the serial number of the process, eg : 1. Then hit ENTER.
* [1]: 12272 com.intellij.database.remote.RemoteJdbcServer
  [2]: 12340
  [3]: 14628 org.jetbrains.jps.cmdline.Launcher
  [4]: 19796 com.intellij.database.remote.RemoteJdbcServer
  [5]: 13272 com.chinacscs.portal.StarterApplication
  [6]: 20520 org.jetbrains.idea.maven.server.RemoteMavenServer36
  [7]: 10396
  [8]: 3564 com.intellij.database.remote.RemoteJdbcServer
5
[INFO] arthas home: C:\Users\yinshuang\.arthas\lib\3.6.2\arthas
[INFO] Try to attach process 13272
[INFO] Found java home from System Env JAVA_HOME: D:\software-work\Java\jdk1.8.0_251
[INFO] Attach process 13272 success.
[INFO] arthas-client connect 127.0.0.1 3658
  ,---.  ,------. ,--------.,--.  ,--.  ,---.   ,---.
 /  O  \ |  .--. ''--.  .--'|  '--'  | /  O  \ '   .-'
|  .-.  ||  '--'.'   |  |   |  .--.  ||  .-.  |`.  `-.
|  | |  ||  |\  \    |  |   |  |  |  ||  | |  |.-'    |
`--' `--'`--' '--'   `--'   `--'  `--'`--' `--'`-----'

wiki       https://arthas.aliyun.com/doc
tutorials  https://arthas.aliyun.com/doc/arthas-tutorials.html
version    3.6.2
main_class
pid        13272
time       2022-08-04 17:33:58

[arthas@13272]$

启动成功后，选择自己想要监听的java进程（例如这里我输入了5，选择了com.chinacscs.portal.StarterApplication这个java进程），接下来可以直接在[arthas@13272]$后输入Arthus命令，也可以通过浏览器访问本地远程端口输入命令，从arthas-client connect可以看出Arthus启动生成远程访问地址是http://127.0.0.1:3658

3.使用案例

大多数场景下，watch和trace命令可以解决大多数问题
如果对watch和trace命令用法不熟也没关系，这里推荐IDEA里的Arthas-idea 插件，
在代码里选中需要监控的方法，鼠标右键Arthus Commond选中对应的命令即可生成命令

(1) 打印日志

Java代码

private void getIllegalPfcompy(Map<String, Object> dataMap) {
  queryBO.setPage(true);
  queryBO.setField(FieldEnum.manager_scale.name());
  List<IllegalPfcompyVO> illegalPfcompyByManagerScale =
      Optional.ofNullable(quarterReportMapper.getIllegalPfcompany(queryBO))
      .orElse(Collections.emptyList());

  queryBO.setField(FieldEnum.person_num.name());
  List<IllegalPfcompyVO> illegalPfcompyByPersonNum =
      Optional.ofNullable(quarterReportMapper.getIllegalPfcompany(queryBO))
      .orElse(Collections.emptyList());
  dataMap.put("illegalPfcompyByManagerScale", illegalPfcompyByManagerScale);
  dataMap.put("illegalPfcompyByPersonNum", illegalPfcompyByPersonNum);
  // 私募机构总数
  if(Objects.nonNull(queryBO.getPageInfo())) {
      mapAddRiskTitleCount(dataMap, queryBO, "illegal_pfcompy");
  }
}

watch命令打印getIllegalPfcompany方法入参、返回结果及异常
（**-n** 表示指定执行次数，**-x** 表示遍历方法深度）

[arthas@17192]$ watch com.chinacscs.portal.customize.mapper.CustomizeQuarterReportMapper getIllegalPfcompany '{params,returnObj,throwExp}'  -n 5  -x 3
Press Q or Ctrl+C to abort.
Affect(class count: 2 , method count: 1) cost in 627 ms, listenerId: 1
method=com.sun.proxy.$Proxy198.getIllegalPfcompany location=AtExceptionExit
ts=2022-08-08 15:57:57; [cost=1599.6962ms] result=@ArrayList[
    @Object[][
        @QuarterReportQueryBO[
            dataPeriod=@String[2022Q2],
            simpleFlag=@Boolean[false],
            authType=null,
            registerDistricts=null,
            workDistricts=null,
            dataType=null,
            field=@String[manager_scale],
            type=@Integer[3],
            keyword=null,
            pageInfo=@PageInfo[PageInfo(totalPage=null, totalCount=null, current=0, size=20, sort=null)],
            pagination=@Boolean[true],
        ],
    ],
    null,
    org.springframework.jdbc.BadSqlGrammarException:
### Error querying database.  Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from sz_pfcompy_basicinfo spb
            inner join sz_pfcompy_basicinfo_attr s' at line 19
### The error may exist in file [E:\chinacscs-project\qfhChina\dev_branch\my\back\portal.customize\target\classes\mappers\CustomizeQuarterReportMapper.xml]
### The error may involve defaultParameterMap
### The error occurred while setting parameters
### SQL: select * from (             select                           spb.company_id,         spb.company_nm,         spb.reg_cd,         sdb0.dict_name as org_type,         ifnull(spb.fund_net_assets/10000.0, 0) as manager_scale,         ifnull(spb.person_num, 0) as person_num,         spba.register_district,         if(spba.work_region = '深圳市', spba.work_district, spba.work_region) as work_district,         spb.sharehd_type      ,                 ifnull(spb.part_no_regist_one_num, 0) as free_num,                 ifnull(spb.branch_num, 0) as branch_num,    ifnull(spird.hit_num, 0) as hit_num,                 ifnull(spird2.hit_num, 0) as sale_num,                 ifnull(spfr.hit_num, 0) as finance_num,             from sz_pfcompy_basicinfo spb             inner join sz_pfcompy_basicinfo_attr spba on spba.company_id = spb.company_id             left join (                 select                     company_id,                     count(distinct hit_company_id) as hit_num                 from sz_pfcompy_illegal_risk_detail                 group by company_id             ) spird on spird.company_id = spb.company_id      left join (                 select                     company_id,                     count(distinct hit_company_id) as hit_num                 from sz_pfcompy_illegal_risk_detail           where illegal_type = 1                 group by company_id             ) spird2 on spird2.company_id = spb.company_id             left join sz_pfcompy_finance_risk spfr on spfr.company_id = spb.company_id                       left join system_dict_basic sdb0 on sdb0.dict_code = spb.type_distribute and sdb0.dict_typed = 'org_type_snm'                    WHERE (spb.part_no_regist_one_num > 0 or spb.branch_num > 0 or spird.hit_num > 0)          ) t                                 order by manager_scale desc limit 0,20
### Cause: java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from sz_pfcompy_basicinfo spb
            inner join sz_pfcompy_basicinfo_attr s' at line 19
; bad SQL grammar []; nested exception is java.sql.SQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from sz_pfcompy_basicinfo spb
            inner join sz_pfcompy_basicinfo_attr s' at line 19
        at org.springframework.jdbc.support.SQLErrorCodeSQLExceptionTranslator.doTranslate(SQLErrorCodeSQLExceptionTranslator.java:235)
        at org.springframework.jdbc.support.AbstractFallbackSQLExceptionTranslator.translate(AbstractFallbackSQLExceptionTranslator.java:72)
        at org.mybatis.spring.MyBatisExceptionTranslator.translateExceptionIfPossible(MyBatisExceptionTranslator.java:73)
        at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:446)
        at com.sun.proxy.$Proxy174.selectList(Unknown Source)
        at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:230)
        at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.executeForMany(MybatisMapperMethod.java:168)
        at com.baomidou.mybatisplus.core.override.MybatisMapperMethod.execute(MybatisMapperMethod.java:82)
        at com.baomidou.mybatisplus.core.override.MybatisMapperProxy.invoke(MybatisMapperProxy.java:61)
        at com.sun.proxy.$Proxy198.getIllegalPfcompany(Unknown Source)
        at com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl.getIllegalPfcompy(CustomizeQuarterReportServiceImpl.java:573)
        at com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl.getPfcomyRiskSituation(CustomizeQuarterReportServiceImpl.java:527)
        at com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl.getDataMap(CustomizeQuarterReportServiceImpl.java:177)
        at com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl.getQuarterReport(CustomizeQuarterReportServiceImpl.java:74)
        at com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl$$FastClassBySpringCGLIB$$1.invoke(<generated>)

根据上面打印日志发现getIllegalPfcompany方法抛出BadSqlGrammarException，排查发现sql最后一个字段多了一个逗号，修改后重新调用接口，查看日志结果：

[arthas@17192]$ watch com.chinacscs.portal.customize.mapper.CustomizeQuarterReportMapper getIllegalPfcompany '{params,returnObj,throwExp}'  -n 5  -x 3
Press Q or Ctrl+C to abort.
Affect(class count: 2 , method count: 1) cost in 234 ms, listenerId: 2
method=com.sun.proxy.$Proxy198.getIllegalPfcompany location=AtExit
ts=2022-08-08 16:10:52; [cost=112.460799ms] result=@ArrayList[
    @Object[][
        @QuarterReportQueryBO[
            dataPeriod=@String[2022Q2],
            simpleFlag=@Boolean[false],
            authType=null,
            registerDistricts=null,
            workDistricts=null,
            dataType=null,
            field=@String[manager_scale],
            type=@Integer[3],
            keyword=null,
            pageInfo=@PageInfo[PageInfo(totalPage=92, totalCount=1825, current=0, size=20, sort=null)],
            pagination=@Boolean[true],
        ],
    ],
    @ArrayList[
        @IllegalPfcompyVO[
            freeNum=@Long[24],
            branchNum=@Long[0],
            saleNum=@Long[0],
            financeNum=@Long[0],
            staffDiffNum=null,
            companyId=@Long[181233],
            companyNm=@String[招银国际资本管理(深圳)有限公司],
            regCd=@String[P1009831],
            orgType=@String[股权、创投类],
            managerScale=@Double[1222.1668946982],
            personNum=@Long[1],
            registerDistrict=@String[前海深港合作区],
            workDistrict=@String[福田区],
            sharehdType=@String[其他（控股主体性质不明或无控股主体）],
        ],
        ... 此处省略18条数据
        ,
        @IllegalPfcompyVO[
            freeNum=@Long[1],
            branchNum=@Long[0],
            saleNum=@Long[0],
            financeNum=@Long[33],
            staffDiffNum=null,
            companyId=@Long[11144793],
            companyNm=@String[深圳市鲲鹏股权投资管理有限公司],
            regCd=@String[P1065379],
            orgType=@String[股权、创投类],
            managerScale=@Double[136.4426374117],
            personNum=@Long[0],
            registerDistrict=@String[前海深港合作区],
            workDistrict=@String[福田区],
            sharehdType=@String[国有控股],
        ],
    ],
    null,
]
method=com.sun.proxy.$Proxy198.getIllegalPfcompany location=AtExit
ts=2022-08-08 16:10:52; [cost=111.184201ms] result=@ArrayList[
    @Object[][
        @QuarterReportQueryBO[
            dataPeriod=@String[2022Q2],
            simpleFlag=@Boolean[false],
            authType=null,
            registerDistricts=null,
            workDistricts=null,
            dataType=null,
            field=@String[person_num],
            type=@Integer[3],
            keyword=null,
            pageInfo=@PageInfo[PageInfo(totalPage=92, totalCount=1825, current=0, size=20, sort=null)],
            pagination=@Boolean[true],
        ],
    ],
    @ArrayList[
        @IllegalPfcompyVO[
            freeNum=@Long[17],
            branchNum=@Long[0],
            saleNum=@Long[0],
            financeNum=@Long[0],
            staffDiffNum=null,
            companyId=@Long[121285],
            companyNm=@String[深圳市思道科投资有限公司],
            regCd=@String[P1006687],
            orgType=@String[证券投资类],
            managerScale=@Double[123.220073605],
            personNum=@Long[3302],
            registerDistrict=@String[福田区],
            workDistrict=@String[福田区],
            sharehdType=null,
        ],
        ... 此处省略18条数据
        ,
        @IllegalPfcompyVO[
            freeNum=@Long[3],
            branchNum=@Long[0],
            saleNum=@Long[0],
            financeNum=@Long[1],
            staffDiffNum=null,
            companyId=@Long[319280],
            companyNm=@String[深圳市中债投资基金管理有限公司],
            regCd=@String[P1002504],
            orgType=@String[证券投资类],
            managerScale=@Double[2.111088045],
            personNum=@Long[299],
            registerDistrict=@String[福田区],
            workDistrict=@String[北京市],
            sharehdType=@String[自然人及其所控制民营企业控股],
        ],
    ],
    null,
]

修复sql问题后，两次调用getIllegalPfcompany方法正常返回20条数据

(2) 性能调优

Java代码

private void getPfcomyRiskSituation(Map<String, Object> dataMap) {
  if(!queryBO.getSimpleFlag()) {
      // （一）涉非线索（简版无）
      getIllegalPfcompy(dataMap);
      // （二）流动性风险 2.多投一风险（简版无）
      getManyInvestPfcompy(dataMap);
      // （六）疑似自融自用（简版无）
      getSelfInvestPfcompy(dataMap);
      // （七）疑似名股实债（简版无）
      getCreditPfcompy(dataMap);
      // （十三）涉房地产领域线索（简版无）
      getEstatePfcompy(dataMap);
      // （十五）涉文娱体育教育线索（简版无）
      getSportPfcompy(dataMap);
      // （十七）公司治理风险（简版无）
      getGovernancePfcompy(dataMap);
      // （十八）命中多个指标风险（简版无）
      getManyIndicatorPfcompy(dataMap);
  }
  // （二）流动性风险 1.逾期风险
  getOverduePfcompy(dataMap);
  // （三）涉稳涉众线索 1.涉稳线索
  getStabilityPfcompy(dataMap);
  // （三）涉稳涉众线索 2.涉众线索
  getPublicPfcompy(dataMap);
  // （四）关联多家私募机构
  getLinkPfcompy(dataMap);
  // （五）关联销售机构线索
  getSalePfcompy(dataMap);
  // （八）注销情况
  getCancelPfcompy(dataMap);
  // （九）“僵尸机构”风险
  getZombiePfcompy(dataMap);
  // （十）异常经营风险
  getAbnormalPfcompy(dataMap);
  // （十一）异地经营风险
  getAddressPfcompy(dataMap);
  // （十二）体外游离风险
  getFreePfcompy(dataMap);
  // （十四）涉类金融领域线索
  getFinancePfcompy(dataMap);
  // （十六）诚信风险
  getIntegrityPfcompy(dataMap);
}

trace命令打印getPfcomyRiskSituation方法耗时

[arthas@21436]$ trace com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl getPfcomyRiskSituation -n 5
Press Q or Ctrl+C to abort.
Affect(class count: 2 , method count: 1) cost in 215 ms, listenerId: 3
`---ts=2022-08-05 14:31:59;thread_name=http-nio-7050-exec-9;id=d6;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@5dc7391e
    `---[88260.3013ms] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getPfcomyRiskSituation()
        +---[0.00% 0.0132ms ] com.chinacscs.portal.customize.bo.QuarterReportQueryBO:getSimpleFlag() #525
        +---[0.27% 241.1679ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getIllegalPfcompy() #527
        +---[0.15% 129.4763ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getManyInvestPfcompy() #529
        +---[0.19% 166.708ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSelfInvestPfcompy() #531
        +---[0.23% 198.81ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getCreditPfcompy() #533
        +---[0.21% 181.1832ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getEstatePfcompy() #535
        +---[0.22% 190.2776ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSportPfcompy() #537
        +---[0.67% 595.3843ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getGovernancePfcompy() #539
        +---[0.12% 104.5043ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getManyIndicatorPfcompy() #541
        +---[0.47% 418.4127ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getOverduePfcompy() #544
        +---[0.20% 178.5491ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getStabilityPfcompy() #546
        +---[0.15% 136.0067ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getPublicPfcompy() #548
        +---[0.21% 188.4806ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getLinkPfcompy() #550
        +---[0.21% 189.3749ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSalePfcompy() #552
        +---[0.46% 402.57ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getCancelPfcompy() #554
        +---[0.25% 216.3849ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getZombiePfcompy() #556
        +---[0.23% 198.8549ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getAbnormalPfcompy() #558
        +---[0.24% 209.4301ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getAddressPfcompy() #560
        +---[0.19% 171.6212ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getFreePfcompy() #562
        +---[0.27% 236.4536ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getFinancePfcompy() #564
        `---[95.07% 83906.2083ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getIntegrityPfcompy() #566

根据trace打印的日志，可以看出getIntegrityPfcompy方法为主要耗时方法，共耗时约83.9s，经排查发现发现getIntegrityPfcompy方法内存在慢sql(关联的字段的字符集不同utf8/utf8mb4)，修改字符集保持一致后重新调用接口，日志如下，看出getIntegrityPfcompy方法耗时大大优化，共耗时约0.4s

`---ts=2022-08-05 15:11:46;thread_name=http-nio-7050-exec-7;id=d4;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@5dc7391e
    `---[4598.4714ms] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getPfcomyRiskSituation()
        +---[0.00% 0.0067ms ] com.chinacscs.portal.customize.bo.QuarterReportQueryBO:getSimpleFlag() #525
        +---[5.27% 242.1928ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getIllegalPfcompy() #527
        +---[2.90% 133.4938ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getManyInvestPfcompy() #529
        +---[3.62% 166.5516ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSelfInvestPfcompy() #531
        +---[3.86% 177.3487ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getCreditPfcompy() #533
        +---[3.88% 178.4002ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getEstatePfcompy() #535
        +---[4.24% 195.1286ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSportPfcompy() #537
        +---[11.87% 545.6152ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getGovernancePfcompy() #539
        +---[1.66% 76.1867ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getManyIndicatorPfcompy() #541
        +---[7.62% 350.1765ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getOverduePfcompy() #544
        +---[4.12% 189.2418ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getStabilityPfcompy() #546
        +---[2.89% 132.8539ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getPublicPfcompy() #548
        +---[3.76% 173.0227ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getLinkPfcompy() #550
        +---[3.08% 141.7254ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getSalePfcompy() #552
        +---[9.11% 418.9818ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getCancelPfcompy() #554
        +---[5.07% 233.23ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getZombiePfcompy() #556
        +---[4.63% 212.9978ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getAbnormalPfcompy() #558
        +---[4.74% 218.0598ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getAddressPfcompy() #560
        +---[4.03% 185.4178ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getFreePfcompy() #562
        +---[5.14% 236.3087ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getFinancePfcompy() #564
        `---[8.51% 391.1609ms ] com.chinacscs.portal.customize.service.impl.CustomizeQuarterReportServiceImpl:getIntegrityPfcompy() #566

补充说明：若想了解更高级的用法可以参考Arthus官方文档

本文作者： yinshuang
本文链接： https://yinshuang007.github.io/2023/02/12/Java应用诊断利器-Arthus/
版权声明： 本博客所有文章除特别声明外，均采用 MIT 许可协议。转载请注明出处！