背景
公司有个渠道系统，专门对接三方渠道使用，没有什么业务逻辑，主要是转换报文和参数校验之类的工作，起着一个承上启下的作用。
最近在优化接口的响应时间，优化了代码之后，但是时间还是达不到要求；有一个诡异的100ms左右的耗时问题，在接口中打印了请求处理时间后，和调用方的响应时间还有差了100ms左右。比如程序里记录150ms，但是调用方等待时间却为250ms左右。
下面记录下当时详细的定位&解决流程（其实解决很简单，关键在于怎么定位并找到解决问题的方法）
基于 Spring Boot + MyBatis Plus + Vue & Element 实现的后台管理系统 + 用户小程序，支持 RBAC 动态权限、多租户、数据权限、工作流、三方登录、支付、短信、商城等功能
定位过程
分析代码
渠道系统是一个常见的spring-boot web工程，使用了集成的tomcat。分析了代码之后，发现并没有特殊的地方，没有特殊的过滤器或者拦截器，所以初步排除是业务代码问题
分析调用流程
出现这个问题之后，首先确认了下接口的调用流程。由于是内部测试，所以调用流程较少。
Nginx -反向代理-> 渠道系统
公司是云服务器，网络走的也是云的内网。由于不明确问题的原因，所以用排除法，首先确认服务器网络是否有问题。
先确认发送端到Nginx Host是否有问题：
[jboss@VM_0_139_centos ~]$ ping 10.0.0.139 PING 10.0.0.139 (10.0.0.139) 56(84) bytes of data. 64 bytes from 10.0.0.139: icmp_seq=1 ttl=64 time=0.029 ms 64 bytes from 10.0.0.139: icmp_seq=2 ttl=64 time=0.041 ms 64 bytes from 10.0.0.139: icmp_seq=3 ttl=64 time=0.040 ms 64 bytes from 10.0.0.139: icmp_seq=4 ttl=64 time=0.040 ms
从ping结果上看，发送端到Nginx主机的延迟是无问题的，接下来查看Nginx到渠道系统的网络。
> 基于 Spring Cloud Alibaba + Gateway + Nacos + RocketMQ + Vue & Element 实现的后台管理系统 + 用户小程序，支持 RBAC 动态权限、多租户、数据权限、工作流、三方登录、支付、短信、商城等功能 > > * 项目地址：<https://gitee.com/zhijiantianya/yudao-cloud> > * 视频教程：<https://doc.iocoder.cn/video/> # 由于日志是没问题的，这里直接复制上面日志了 [jboss@VM_0_139_centos ~]$ ping 10.0.0.139 PING 10.0.0.139 (10.0.0.139) 56(84) bytes of data. 64 bytes from 10.0.0.139: icmp_seq=1 ttl=64 time=0.029 ms 64 bytes from 10.0.0.139: icmp_seq=2 ttl=64 time=0.041 ms 64 bytes from 10.0.0.139: icmp_seq=3 ttl=64 time=0.040 ms 64 bytes from 10.0.0.139: icmp_seq=4 ttl=64 time=0.040 ms
从ping结果上看，Nginx到渠道系统服务器网络延迟也是没问题的
既然网络看似没问题，那么可以继续排除法，砍掉Nginx，客户端直接再渠道系统的服务器上，通过回环地址（localhost）直连，避免经过网卡/dns，缩小问题范围看看能否复现（这个应用和地址是我后期模拟的，测试的是一个空接口）：
[jboss@VM_10_91_centos tmp]$ curl -w "@curl-time.txt" http://127.0.0.1:7744/send success http: 200 dns: 0.001s redirect: 0.000s time_connect: 0.001s time_appconnect: 0.000s time_pretransfer: 0.001s time_starttransfer: 0.073s size_download: 7bytes speed_download: 95.000B/s ---------- time_total: 0.073s 请求总耗时
从curl日志上看，通过回环地址调用一个空接口耗时也有73ms。这就奇怪了，跳过了中间所有调用节点（包括过滤器&拦截器之类），直接请求应用一个空接口，都有73ms的耗时，再请求一次看看：
[jboss@VM_10_91_centos tmp]$ curl -w "@curl-time.txt" http://127.0.0.1:7744/send success http: 200 dns: 0.001s redirect: 0.000s time_connect: 0.001s time_appconnect: 0.000s time_pretransfer: 0.001s time_starttransfer: 0.003s size_download: 7bytes speed_download: 2611.000B/s ---------- time_total: 0.003s
更奇怪的是，第二次请求耗时就正常了，变成了3ms。经查阅资料，linux curl是默认开启http keep-alive的。就算不开启keep-alive，每次重新handshake，也不至于需要70ms。
经过不断分析测试发现，连续请求的话时间就会很短，每次请求只需要几毫秒，但是如果隔一段时间再请求，就会花费70ms以上。
从这个现象猜想，可能是某些缓存机制导致的，连续请求因为有缓存，所以速度快，时间长缓存失效后导致时间长。
那么这个问题点到底在哪一层呢？tomcat层还是spring-webmvc呢？
光猜想定位不了问题，还是得实际测试一下，把渠道系统的代码放到本地ide里启动测试能否复现
但是导入本地Ide后，在Ide中启动后并不能复现问题，并没有70+ms的延迟问题。这下头疼了，本地无法复现，不能Debug，由于问题点不在业务代码，也不能通过加日志的方式来Debug
这时候可以祭出神器Arthas了
Arthas分析问题
Arthas 是Alibaba开源的Java诊断工具，深受开发者喜爱。当你遇到以下类似问题而束手无策时，Arthas可以帮助你解决：
- 这个类从哪个 jar 包加载的？为什么会报各种类相关的 Exception？
- 我改的代码为什么没有执行到？难道是我没 commit？分支搞错了？
- 遇到问题无法在线上 debug，难道只能通过加日志再重新发布吗？
- 线上遇到某个用户的数据处理有问题，但线上同样无法 debug，线下无法重现！
- 是否有一个全局视角来查看系统的运行状况？
- 有什么办法可以监控到JVM的实时运行状态？
上面是Arthas的官方简介，这次我只需要用他的一个小功能trace。动态计算方法调用路径和时间，这样我就可以定位时间在哪个地方被消耗了。
- trace 方法内部调用路径，并输出方法路径上的每个节点上耗时
- trace 命令能主动搜索 class-pattern／method-pattern
- 对应的方法调用路径，渲染和统计整个调用链路上的所有性能开销和追踪调用链路。
有了神器，那么该追踪什么方法呢？由于我对Tomcat源码不是很熟，所以只能从spring mvc下手，先来trace一下spring mvc的入口：
[arthas@24851]$ trace org.springframework.web.servlet.DispatcherServlet * Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:44) cost in 508 ms. `---ts=2019-09-14 21:07:44;thread_name=http-nio-7744-exec-2;id=11;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@7c136917 `---[2.952142ms] org.springframework.web.servlet.DispatcherServlet:buildLocaleContext() `---ts=2019-09-14 21:07:44;thread_name=http-nio-7744-exec-2;id=11;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@7c136917 `---[18.08903ms] org.springframework.web.servlet.DispatcherServlet:doService() +---[0.041346ms] org.apache.commons.logging.Log:isDebugEnabled() #889 +---[0.022398ms] org.springframework.web.util.WebUtils:isIncludeRequest() #898 +---[0.014904ms] org.springframework.web.servlet.DispatcherServlet:getWebApplicationContext() #910 +---[1.071879ms] javax.servlet.http.HttpServletRequest:setAttribute() #910 +---[0.020977ms] javax.servlet.http.HttpServletRequest:setAttribute() #911 +---[0.017073ms] javax.servlet.http.HttpServletRequest:setAttribute() #912 +---[0.218277ms] org.springframework.web.servlet.DispatcherServlet:getThemeSource() #913 | `---[0.137568ms] org.springframework.web.servlet.DispatcherServlet:getThemeSource() | `---[min=0.00783ms,max=0.014251ms,total=0.022081ms,count=2] org.springframework.web.servlet.DispatcherServlet:getWebApplicationContext() #782 +---[0.019363ms] javax.servlet.http.HttpServletRequest:setAttribute() #913 +---[0.070694ms] org.springframework.web.servlet.FlashMapManager:retrieveAndUpdate() #916 +---[0.01839ms] org.springframework.web.servlet.FlashMap:<init>() #920 +---[0.016943ms] javax.servlet.http.HttpServletRequest:setAttribute() #920 +---[0.015268ms] javax.servlet.http.HttpServletRequest:setAttribute() #921 +---[15.050124ms] org.springframework.web.servlet.DispatcherServlet:doDispatch() #925 | `---[14.943477ms] org.springframework.web.servlet.DispatcherServlet:doDispatch() | +---[0.019135ms] org.springframework.web.context.request.async.WebAsyncUtils:getAsyncManager() #953 | +---[2.108373ms] org.springframework.web.servlet.DispatcherServlet:checkMultipart() #960 | | `---[2.004436ms] org.springframework.web.servlet.DispatcherServlet:checkMultipart() | | `---[1.890845ms] org.springframework.web.multipart.MultipartResolver:isMultipart() #1117 | +---[2.054361ms] org.springframework.web.servlet.DispatcherServlet:getHandler() #964 | | `---[1.961963ms] org.springframework.web.servlet.DispatcherServlet:getHandler() | | +---[0.02051ms] java.util.List:iterator() #1183 | | +---[min=0.003805ms,max=0.009641ms,total=0.013446ms,count=2] java.util.Iterator:hasNext() #1183 | | +---[min=0.003181ms,max=0.009751ms,total=0.012932ms,count=2] java.util.Iterator:next() #1183 | | +---[min=0.005841ms,max=0.015308ms,total=0.021149ms,count=2] org.apache.commons.logging.Log:isTraceEnabled() #1184 | | `---[min=0.474739ms,max=1.19145ms,total=1.666189ms,count=2] org.springframework.web.servlet.HandlerMapping:getHandler() #1188 | +---[0.013071ms] org.springframework.web.servlet.HandlerExecutionChain:getHandler() #971 | +---[0.372236ms] org.springframework.web.servlet.DispatcherServlet:getHandlerAdapter() #971 | | `---[0.280073ms] org.springframework.web.servlet.DispatcherServlet:getHandlerAdapter() | | +---[0.004804ms] java.util.List:iterator() #1224 | | +---[0.003668ms] java.util.Iterator:hasNext() #1224 | | +---[0.003038ms] java.util.Iterator:next() #1224 | | +---[0.006451ms] org.apache.commons.logging.Log:isTraceEnabled() #1225 | | `---[0.012683ms] org.springframework.web.servlet.HandlerAdapter:supports() #1228 | +---[0.012848ms] javax.servlet.http.HttpServletRequest:getMethod() #974 | +---[0.013132ms] java.lang.String:equals() #975 | +---[0.003025ms] org.springframework.web.servlet.HandlerExecutionChain:getHandler() #977 | +---[0.008095ms] org.springframework.web.servlet.HandlerAdapter:getLastModified() #977 | +---[0.006596ms] org.apache.commons.logging.Log:isDebugEnabled() #978 | +---[0.018024ms] org.springframework.web.context.request.ServletWebRequest:<init>() #981 | +---[0.017869ms] org.springframework.web.context.request.ServletWebRequest:checkNotModified() #981 | +---[0.038542ms] org.springframework.web.servlet.HandlerExecutionChain:applyPreHandle() #986 | +---[0.00431ms] org.springframework.web.servlet.HandlerExecutionChain:getHandler() #991 | +---[4.248493ms] org.springframework.web.servlet.HandlerAdapter:handle() #991 | +---[0.014805ms] org.springframework.web.context.request.async.WebAsyncManager:isConcurrentHandlingStarted() #993 | +---[1.444994ms] org.springframework.web.servlet.DispatcherServlet:applyDefaultViewName() #997 | | `---[0.067631ms] org.springframework.web.servlet.DispatcherServlet:applyDefaultViewName() | +---[0.012027ms] org.springframework.web.servlet.HandlerExecutionChain:applyPostHandle() #998 | +---[0.373997ms] org.springframework.web.servlet.DispatcherServlet:processDispatchResult() #1008 | | `---[0.197004ms] org.springframework.web.servlet.DispatcherServlet:processDispatchResult() | | +---[0.007074ms] org.apache.commons.logging.Log:isDebugEnabled() #1075 | | +---[0.005467ms] org.springframework.web.context.request.async.WebAsyncUtils:getAsyncManager() #1081 | | +---[0.004054ms] org.springframework.web.context.request.async.WebAsyncManager:isConcurrentHandlingStarted() #1081 | | `---[0.011988ms] org.springframework.web.servlet.HandlerExecutionChain:triggerAfterCompletion() #1087 | `---[0.004015ms] org.springframework.web.context.request.async.WebAsyncManager:isConcurrentHandlingStarted() #1018 +---[0.005055ms] org.springframework.web.context.request.async.WebAsyncUtils:getAsyncManager() #928 `---[0.003422ms] org.springframework.web.context.request.async.WebAsyncManager:isConcurrentHandlingStarted() #928
~
[jboss@VM_10_91_centos tmp]$ curl -w "@curl-time.txt" http://127.0.0.1:7744/send success http: 200 dns: 0.001s redirect: 0.000s time_connect: 0.001s time_appconnect: 0.000s time_pretransfer: 0.001s time_starttransfer: 0.115s size_download: 7bytes speed_download: 60.000B/s ---------- time_total: 0.115s
本次调用，调用端时间花费115ms，但是从arthas trace上看，spring mvc只消耗了18ms，那么剩下的97ms去哪了呢？
本地测试后已经可以排除spring mvc的问题了，最后也是唯一可能出问题的点就是tomcat
可是本人并不熟悉tomcat中的源码，就连请求入口都不清楚，tomcat里需要trace的类都不好找。。。
不过没关系，有神器Arthas，可以通过stack命令来反向查找调用路径，以org.springframework.web.servlet.DispatcherServlet作为参数：
stack 输出当前方法被调用的调用路径
很多时候我们都知道一个方法被执行，但这个方法被执行的路径非常多，或者你根本就不知道这个方法是从那里被执行了，此时你需要的是 stack 命令。
[arthas@24851]$ stack org.springframework.web.servlet.DispatcherServlet * Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:44) cost in 495 ms. ts=2019-09-14 21:15:19;thread_name=http-nio-7744-exec-5;id=14;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@7c136917 @org.springframework.web.servlet.FrameworkServlet.processRequest() at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:866) at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1468) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748) ts=2019-09-14 21:15:19;thread_name=http-nio-7744-exec-5;id=14;is_daemon=true;priority=5;TCCL=org.springframework.boot.web.embedded.tomcat.TomcatEmbeddedWebappClassLoader@7c136917 @org.springframework.web.servlet.DispatcherServlet.doService() at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:866) at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:851) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:109) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:496) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:790) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1468) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748)
从stack日志上可以很直观的看出DispatchServlet的调用栈，那么这么长的路径，该trace哪个类呢（这里跳过spring mvc中的过滤器的trace过程，实际排查的时候也trace了一遍，但这诡异的时间消耗不是由这里过滤器产生的）？
有一定经验的老司机从名字上大概也能猜出来从哪里下手比较好，那就是org.apache.coyote.http11.Http11Processor.service，从名字上看，http1.1处理器，这可能是一个比较好的切入点。下面来trace一下：
[arthas@24851]$ trace org.apache.coyote.http11.Http11Processor service Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:1) cost in 269 ms. `---ts=2019-09-14 21:22:51;thread_name=http-nio-7744-exec-8;id=17;is_daemon=true;priority=5;TCCL=org.springframework.boot.loader.LaunchedURLClassLoader@20ad9418 `---[131.650285ms] org.apache.coyote.http11.Http11Processor:service() +---[0.036851ms] org.apache.coyote.Request:getRequestProcessor() #667 +---[0.009986ms] org.apache.coyote.RequestInfo:setStage() #668 +---[0.008928ms] org.apache.coyote.http11.Http11Processor:setSocketWrapper() #671 +---[0.013236ms] org.apache.coyote.http11.Http11InputBuffer:init() #672 +---[0.00981ms] org.apache.coyote.http11.Http11OutputBuffer:init() #673 +---[min=0.00213ms,max=0.007317ms,total=0.009447ms,count=2] org.apache.coyote.http11.Http11Processor:getErrorState() #683 +---[min=0.002098ms,max=0.008888ms,total=0.010986ms,count=2] org.apache.coyote.ErrorState:isError() #683 +---[min=0.002448ms,max=0.007149ms,total=0.009597ms,count=2] org.apache.coyote.http11.Http11Processor:isAsync() #683 +---[min=0.002399ms,max=0.00852ms,total=0.010919ms,count=2] org.apache.tomcat.util.net.AbstractEndpoint:isPaused() #683 +---[min=0.033587ms,max=0.11832ms,total=0.151907ms,count=2] org.apache.coyote.http11.Http11InputBuffer:parseRequestLine() #687 +---[0.005384ms] org.apache.tomcat.util.net.AbstractEndpoint:isPaused() #695 +---[0.007924ms] org.apache.coyote.Request:getMimeHeaders() #702 +---[0.006744ms] org.apache.tomcat.util.net.AbstractEndpoint:getMaxHeaderCount() #702 +---[0.012574ms] org.apache.tomcat.util.http.MimeHeaders:setLimit() #702 +---[0.14319ms] org.apache.coyote.http11.Http11InputBuffer:parseHeaders() #703 +---[0.003997ms] org.apache.coyote.Request:getMimeHeaders() #743 +---[0.026561ms] org.apache.tomcat.util.http.MimeHeaders:values() #743 +---[min=0.002869ms,max=0.01203ms,total=0.014899ms,count=2] java.util.Enumeration:hasMoreElements() #745 +---[0.070114ms] java.util.Enumeration:nextElement() #746 +---[0.010921ms] java.lang.String:toLowerCase() #746 +---[0.008453ms] java.lang.String:contains() #746 +---[0.002698ms] org.apache.coyote.http11.Http11Processor:getErrorState() #775 +---[0.00307ms] org.apache.coyote.ErrorState:isError() #775 +---[0.002708ms] org.apache.coyote.RequestInfo:setStage() #777 +---[0.171139ms] org.apache.coyote.http11.Http11Processor:prepareRequest() #779 +---[0.009349ms] org.apache.tomcat.util.net.SocketWrapperBase:decrementKeepAlive() #794 +---[0.002574ms] org.apache.coyote.http11.Http11Processor:getErrorState() #800 +---[0.002696ms] org.apache.coyote.ErrorState:isError() #800 +---[0.002499ms] org.apache.coyote.RequestInfo:setStage() #802 +---[0.005641ms] org.apache.coyote.http11.Http11Processor:getAdapter() #803 +---[129.868916ms] org.apache.coyote.Adapter:service() #803 +---[0.003859ms] org.apache.coyote.http11.Http11Processor:getErrorState() #809 +---[0.002365ms] org.apache.coyote.ErrorState:isError() #809 +---[0.003844ms] org.apache.coyote.http11.Http11Processor:isAsync() #809 +---[0.002382ms] org.apache.coyote.Response:getStatus() #809 +---[0.002476ms] org.apache.coyote.http11.Http11Processor:statusDropsConnection() #809 +---[0.002284ms] org.apache.coyote.RequestInfo:setStage() #838 +---[0.00222ms] org.apache.coyote.http11.Http11Processor:isAsync() #839 +---[0.037873ms] org.apache.coyote.http11.Http11Processor:endRequest() #843 +---[0.002188ms] org.apache.coyote.RequestInfo:setStage() #845 +---[0.002112ms] org.apache.coyote.http11.Http11Processor:getErrorState() #849 +---[0.002063ms] org.apache.coyote.ErrorState:isError() #849 +---[0.002504ms] org.apache.coyote.http11.Http11Processor:isAsync() #853 +---[0.009808ms] org.apache.coyote.Request:updateCounters() #854 +---[0.002008ms] org.apache.coyote.http11.Http11Processor:getErrorState() #855 +---[0.002192ms] org.apache.coyote.ErrorState:isIoAllowed() #855 +---[0.01968ms] org.apache.coyote.http11.Http11InputBuffer:nextRequest() #856 +---[0.010065ms] org.apache.coyote.http11.Http11OutputBuffer:nextRequest() #857 +---[0.002576ms] org.apache.coyote.RequestInfo:setStage() #870 +---[0.016599ms] org.apache.coyote.http11.Http11Processor:processSendfile() #872 +---[0.008182ms] org.apache.coyote.http11.Http11InputBuffer:getParsingRequestLinePhase() #688 +---[0.0075ms] org.apache.coyote.http11.Http11Processor:handleIncompleteRequestLineRead() #690 +---[0.001979ms] org.apache.coyote.RequestInfo:setStage() #875 +---[0.001981ms] org.apache.coyote.http11.Http11Processor:getErrorState() #877 +---[0.001934ms] org.apache.coyote.ErrorState:isError() #877 +---[0.001995ms] org.apache.tomcat.util.net.AbstractEndpoint:isPaused() #877 +---[0.002403ms] org.apache.coyote.http11.Http11Processor:isAsync() #879 `---[0.006176ms] org.apache.coyote.http11.Http11Processor:isUpgrade() #881
日志里有一个129ms的耗时点（时间比没开arthas的时候更长是因为arthas本身带来的性能消耗，所以生产环境小心使用），这个就是要找的问题点。
打问题点找到了，那怎么定位是什么导致的问题呢，又如何解决呢？
继续trace吧，细化到具体的代码块或者内容。trace由于性能考虑，不会展示所有的调用路径，如果调用路径过深，只有手动深入trace，原则就是trace耗时长的那个方法：
[arthas@24851]$ trace org.apache.coyote.Adapter service Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:1) cost in 608 ms. `---ts=2019-09-14 21:34:33;thread_name=http-nio-7744-exec-1;id=10;is_daemon=true;priority=5;TCCL=org.springframework.boot.loader.LaunchedURLClassLoader@20ad9418 `---[81.70999ms] org.apache.catalina.connector.CoyoteAdapter:service() +---[0.032546ms] org.apache.coyote.Request:getNote() #302 +---[0.007148ms] org.apache.coyote.Response:getNote() #303 +---[0.007475ms] org.apache.catalina.connector.Connector:getXpoweredBy() #324 +---[0.00447ms] org.apache.coyote.Request:getRequestProcessor() #331 +---[0.007902ms] java.lang.ThreadLocal:get() #331 +---[0.006522ms] org.apache.coyote.RequestInfo:setWorkerThreadName() #331 +---[73.793798ms] org.apache.catalina.connector.CoyoteAdapter:postParseRequest() #336 +---[0.001536ms] org.apache.catalina.connector.Connector:getService() #339 +---[0.004469ms] org.apache.catalina.Service:getContainer() #339 +---[0.007074ms] org.apache.catalina.Engine:getPipeline() #339 +---[0.004334ms] org.apache.catalina.Pipeline:isAsyncSupported() #339 +---[0.002466ms] org.apache.catalina.connector.Request:setAsyncSupported() #339 +---[6.01E-4ms] org.apache.catalina.connector.Connector:getService() #342 +---[0.001859ms] org.apache.catalina.Service:getContainer() #342 +---[9.65E-4ms] org.apache.catalina.Engine:getPipeline() #342 +---[0.005231ms] org.apache.catalina.Pipeline:getFirst() #342 +---[7.239154ms] org.apache.catalina.Valve:invoke() #342 +---[0.006904ms] org.apache.catalina.connector.Request:isAsync() #345 +---[0.00509ms] org.apache.catalina.connector.Request:finishRequest() #372 +---[0.051461ms] org.apache.catalina.connector.Response:finishResponse() #373 +---[0.007244ms] java.util.concurrent.atomic.AtomicBoolean:<init>() #379 +---[0.007314ms] org.apache.coyote.Response:action() #380 +---[0.004518ms] org.apache.catalina.connector.Request:isAsyncCompleting() #382 +---[0.001072ms] org.apache.catalina.connector.Request:getContext() #394 +---[0.007166ms] java.lang.System:currentTimeMillis() #401 +---[0.004367ms] org.apache.coyote.Request:getStartTime() #401 +---[0.011483ms] org.apache.catalina.Context:logAccess() #401 +---[0.0014ms] org.apache.coyote.Request:getRequestProcessor() #406 +---[min=8.0E-4ms,max=9.22E-4ms,total=0.001722ms,count=2] java.lang.Integer:<init>() #406 +---[0.001082ms] java.lang.reflect.Method:invoke() #406 +---[0.001851ms] org.apache.coyote.RequestInfo:setWorkerThreadName() #406 +---[0.035805ms] org.apache.catalina.connector.Request:recycle() #410 `---[0.007849ms] org.apache.catalina.connector.Response:recycle() #411
一段无聊的手动深入trace之后………………
[arthas@24851]$ trace org.apache.catalina.webresources.AbstractArchiveResourceSet getArchiveEntries Press Q or Ctrl+C to abort. Affect(class-cnt:4 , method-cnt:2) cost in 150 ms. `---ts=2019-09-14 21:36:26;thread_name=http-nio-7744-exec-3;id=12;is_daemon=true;priority=5;TCCL=org.springframework.boot.loader.LaunchedURLClassLoader@20ad9418 `---[75.743681ms] org.apache.catalina.webresources.JarWarResourceSet:getArchiveEntries() +---[0.025731ms] java.util.HashMap:<init>() #106 +---[0.097729ms] org.apache.catalina.webresources.JarWarResourceSet:openJarFile() #109 +---[0.091037ms] java.util.jar.JarFile:getJarEntry() #110 +---[0.096325ms] java.util.jar.JarFile:getInputStream() #111 +---[0.451916ms] org.apache.catalina.webresources.TomcatJarInputStream:<init>() #113 +---[min=0.001175ms,max=0.001176ms,total=0.002351ms,count=2] java.lang.Integer:<init>() #114 +---[0.00104ms] java.lang.reflect.Method:invoke() #114 +---[0.045105ms] org.apache.catalina.webresources.TomcatJarInputStream:getNextJarEntry() #114 +---[min=5.02E-4ms,max=0.008531ms,total=0.028864ms,count=31] java.util.jar.JarEntry:getName() #116 +---[min=5.39E-4ms,max=0.022805ms,total=0.054647ms,count=31] java.util.HashMap:put() #116 +---[min=0.004452ms,max=34.479307ms,total=74.206249ms,count=31] org.apache.catalina.webresources.TomcatJarInputStream:getNextJarEntry() #117 +---[0.018358ms] org.apache.catalina.webresources.TomcatJarInputStream:getManifest() #119 +---[0.006429ms] org.apache.catalina.webresources.JarWarResourceSet:setManifest() #120 +---[0.010904ms] org.apache.tomcat.util.compat.JreCompat:isJre9Available() #121 +---[0.003307ms] org.apache.catalina.webresources.TomcatJarInputStream:getMetaInfEntry() #133 +---[5.5E-4ms] java.util.jar.JarEntry:getName() #135 +---[6.42E-4ms] java.util.HashMap:put() #135 +---[0.001981ms] org.apache.catalina.webresources.TomcatJarInputStream:getManifestEntry() #137 +---[0.064484ms] org.apache.catalina.webresources.TomcatJarInputStream:close() #141 +---[0.007961ms] org.apache.catalina.webresources.JarWarResourceSet:closeJarFile() #151 `---[0.004643ms] java.io.InputStream:close() #155
发现了一个值得暂停思考的点：
+---[min=0.004452ms,max=34.479307ms,total=74.206249ms,count=31] org.apache.catalina.webresources.TomcatJarInputStream:getNextJarEntry() #117
这行代码加载了31次，一共耗时74ms；从名字上看，应该是tomcat加载jar包时的耗时，那么是加载了31个jar包的耗时，还是加载了jar包内的某些资源31次耗时呢？
TomcatJarInputStream这个类源码的注释写到：
The purpose of this sub-class is to obtain references to the JarEntry objects for META-INF/ and META-INF/MANIFEST.MF that are otherwise swallowed by the JarInputStream implementation.
大概意思也就是，获取jar包内META-INF/，META-INF/MANIFEST的资源，这是一个子类，更多的功能在父类JarInputStream里。
其实看到这里大概也能猜到问题了，tomcat加载jar包内META-INF/，META-INF/MANIFEST的资源导致的耗时，至于为什么连续请求不会耗时，应该是tomcat的缓存机制（下面介绍源码分析）
不着急定位问题，试着通过Arthas最终定位问题细节，继续手动深入trace
[arthas@24851]$ trace org.apache.catalina.webresources.TomcatJarInputStream * Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:4) cost in 44 ms. `---ts=2019-09-14 21:37:47;thread_name=http-nio-7744-exec-5;id=14;is_daemon=true;priority=5;TCCL=org.springframework.boot.loader.LaunchedURLClassLoader@20ad9418 `---[0.234952ms] org.apache.catalina.webresources.TomcatJarInputStream:createZipEntry() +---[0.039455ms] java.util.jar.JarInputStream:createZipEntry() #43 `---[0.007827ms] java.lang.String:equals() #44 `---ts=2019-09-14 21:37:47;thread_name=http-nio-7744-exec-5;id=14;is_daemon=true;priority=5;TCCL=org.springframework.boot.loader.LaunchedURLClassLoader@20ad9418 `---[0.050222ms] org.apache.catalina.webresources.TomcatJarInputStream:createZipEntry() +---[0.001889ms] java.util.jar.JarInputStream:createZipEntry() #43 `---[0.001643ms] java.lang.String:equals() #46 #这里一共31个trace日志，删减了剩下的
从方法名上看，还是加载资源之类的意思。都已经到jdk源码了，这时候来看一下TomcatJarInputStream这个类的源码:
/** * Creates a new <code>JarEntry</code> (<code>ZipEntry</code>) for the * specified JAR file entry name. The manifest attributes of * the specified JAR file entry name will be copied to the new * <CODE>JarEntry</CODE>. * * @param name the name of the JAR/ZIP file entry * @return the <code>JarEntry</code> object just created */ protected ZipEntry createZipEntry(String name) { JarEntry e = new JarEntry(name); if (man != null) { e.attr = man.getAttributes(name); } return e; }
这个createZipEntry有个name参数，从注释上看，是jar/zip文件名，如果能得到文件名这种关键信息，就可以直接定位问题了；还是通过Arthas，使用watch命令，动态监测方法调用数据
watch方法执行数据观测
让你能方便的观察到指定方法的调用情况。能观察到的范围为：返回值、抛出异常、入参，通过编写 OGNL 表达式进行对应变量的查看。
watch 该方法的入参
[arthas@24851]$ watch org.apache.catalina.webresources.TomcatJarInputStream createZipEntry "{params[0]}" Press Q or Ctrl+C to abort. Affect(class-cnt:1 , method-cnt:1) cost in 27 ms. ts=2019-09-14 21:51:14; [cost=0.14547ms] result=@ArrayList[ @String[META-INF/], ] ts=2019-09-14 21:51:14; [cost=0.048028ms] result=@ArrayList[ @String[META-INF/MANIFEST.MF], ] ts=2019-09-14 21:51:14; [cost=0.046071ms] result=@ArrayList[ @String[META-INF/resources/], ] ts=2019-09-14 21:51:14; [cost=0.033855ms] result=@ArrayList[ @String[META-INF/resources/swagger-ui.html], ] ts=2019-09-14 21:51:14; [cost=0.039138ms] result=@ArrayList[ @String[META-INF/resources/webjars/], ] ts=2019-09-14 21:51:14; [cost=0.033701ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/], ] ts=2019-09-14 21:51:14; [cost=0.033644ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/favicon-16x16.png], ] ts=2019-09-14 21:51:14; [cost=0.033976ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/springfox.css], ] ts=2019-09-14 21:51:14; [cost=0.032818ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/swagger-ui-standalone-preset.js.map], ] ts=2019-09-14 21:51:14; [cost=0.04651ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/swagger-ui.css], ] ts=2019-09-14 21:51:14; [cost=0.034793ms] result=@ArrayList[ @String[META-INF/resources/webjars/springfox-swagger-ui/swagger-ui.js.map],
这下直接看到了具体加载的资源名，这么熟悉的名字：swagger-ui，一个国外的rest接口文档工具，又有国内开发者基于swagger-ui做了一套spring mvc的集成工具，通过注解就可以自动生成swagger-ui需要的接口定义json文件，用起来还比较方便，就是侵入性较强。
删除swagger的jar包后问题，诡异的70+ms就消失了
<!--pom 里删除这两个引用，这两个包时国内开发者封装的，swagger-ui并没有提供java spring-mvc的支持包，swagger只是一个浏览器端的ui+editor --> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger2</artifactId> <version>2.9.2</version> </dependency> <dependency> <groupId>io.springfox</groupId> <artifactId>springfox-swagger-ui</artifactId> <version>2.9.2</version> </dependency>
那么为什么swagger会导致请求耗时呢，为什么每次请求偶读会加载swagger内部的静态资源呢？
其实这是tomcat-embed的一个bug吧，下面详细介绍一下该Bug
Tomcat embed Bug分析&解决
源码分析过程实在太漫长，而且也不是本文的重点，所以就不介绍了， 下面直接介绍下分析结果
顺便贴一张tomcat处理请求的核心类图
为什么每次请求会加载Jar包内的静态资源
关键在于org.apache.catalina.mapper.Mapper#internalMapWrapper这个方法，该版本下处理请求的方式有问题，导致每次都校验静态资源。
为什么连续请求不会出现问题
因为Tomcat对于这种静态资源的解析是有缓存的，优先从缓存查找，缓存过期后再重新解析。具体参考org.apache.catalina.webresources.Cache，默认过期时间ttl是5000ms。
为什么本地不会复现
其实确切的说，是通过spring-boot打包插件后不能复现。由于启动方式的不同，tomcat使用了不同的类去处理静态资源，所以没问题
如何解决
升级tomcat-embed版本即可
当前出现Bug的版本为：
spring-boot:2.0.2.RELEASE，内置的tomcat embed版本为8.5.31
升级tomcat embed版本至8.5.40+即可解决此问题，新版本已经修复了
通过替换springboot pom properties方式
如果项目是maven是继承的springboot，即parent配置为springboot的，或者dependencyManagement中import spring boot包的
<parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.2.RELEASE</version> <relativePath/> <!-- lookup parent from repository --> </parent>
pom中直接覆盖properties即可：
<properties> <tomcat.version>8.5.40</tomcat.version> </properties>
升级spring boot版本
springboot 2.1.0.RELEASE中的tomcat embed版本已经大于8.5.31了，所以直接将springboot升级至该版本及以上版本就可以解决此问题
