一、背景
公司有個渠道系統，專門對接三方渠道使用，沒有什么業務邏輯，主要是轉換報文和參數校驗之類的工作，起著一個承上啟下的作用。
最近在優化接口的響應時間，優化了代碼之后，但是時間還是達不到要求；有一個詭異的100ms左右的耗時問題，在接口中打印了請求處理時間后，和調用方的響應時間還有差了100ms左右。比如程序里記錄150ms，但是調用方等待時間卻為250ms左右。
下面記錄下當時詳細的定位&解決流程（其實解決很簡單，關鍵在于怎么定位并找到解決問題的方法）。
二、定位過程
1.分析代碼
渠道系統是一個常見的spring-boot web工程，使用了集成的Tomcat。分析了代碼之后，發現并沒有特殊的地方，沒有特殊的過濾器或者攔截器，所以初步排除是業務代碼問題。
2.分析調用流程
出現這個問題之后，首先確認了下接口的調用流程。由于是內部測試，所以調用流程較少。
Nginx -反向代理-> 渠道系統
公司是云服務器，網絡走的也是云的內網。由于不明確問題的原因，所以用排除法，首先確認服務器網絡是否有問題。
先確認發送端到Nginx Host是否有問題：
[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
從ping結果上看，發送端到Nginx主機的延遲是無問題的，接下來查看Nginx到渠道系統的網絡。
# 由于日志是沒問題的，這里直接復制上面日志了
[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
從ping結果上看，Nginx到渠道系統服務器網絡延遲也是沒問題的。
既然網絡看似沒問題，那么可以繼續排除法，砍掉Nginx，客戶端直接再渠道系統的服務器上，通過回環地址（localhost）直連，避免經過網卡/DNS，縮小問題范圍看看能否復現（這個應用和地址是我后期模擬的，測試的是一個空接口）：
[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 請求總耗時
從curl日志上看，通過回環地址調用一個空接口耗時也有73ms。這就奇怪了，跳過了中間所有調用節點（包括過濾器&攔截器之類），直接請求應用一個空接口，都有73ms的耗時，再請求一次看看：
[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，第二次請求耗時就正常了，變成了3ms。經查閱資料，linux curl是默認開啟http keep-alive的。就算不開啟keep-alive，每次重新handshake，也不至于需要70ms。
經過不斷分析測試發現，連續請求的話時間就會很短，每次請求只需要幾毫秒，但是如果隔一段時間再請求，就會花費70ms以上。
從這個現象猜想，可能是某些緩存機制導致的，連續請求因為有緩存，所以速度快，時間長緩存失效后導致時間長。
那么這個問題點到底在哪一層呢？tomcat層還是spring-webmvc呢？
光猜想定位不了問題，還是得實際測試一下，把渠道系統的代碼放到本地ide里啟動測試能否復現
但是導入本地Ide后，在Ide中啟動后并不能復現問題，并沒有70+ms的延遲問題。這下頭疼了，本地無法復現，不能Debug，由于問題點不在業務代碼，也不能通過加日志的方式來Debug
這時候可以祭出神器Arthas了。
三、Arthas分析問題
Arthas 是Alibaba開源的JAVA診斷工具，深受開發者喜愛。當你遇到以下類似問題而束手無策時，Arthas可以幫助你解決：
- 這個類從哪個 jar 包加載的？為什么會報各種類相關的 Exception？
- 我改的代碼為什么沒有執行到？難道是我沒 commit？分支搞錯了？
- 遇到問題無法在線上 debug，難道只能通過加日志再重新發布嗎？
- 線上遇到某個用戶的數據處理有問題，但線上同樣無法 debug，線下無法重現！
- 是否有一個全局視角來查看系統的運行狀況？
- 有什么辦法可以監控到JVM的實時運行狀態？
上面是Arthas的官方簡介，這次我只需要用他的一個小功能trace。動態計算方法調用路徑和時間，這樣我就可以定位時間在哪個地方被消耗了。
- trace 方法內部調用路徑，并輸出方法路徑上的每個節點上耗時
- trace 命令能主動搜索 class-pattern／method-pattern
- 對應的方法調用路徑，渲染和統計整個調用鏈路上的所有性能開銷和追蹤調用鏈路。
有了神器，那么該追蹤什么方法呢？由于我對Tomcat源碼不是很熟，所以只能從spring mvc下手，先來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
本次調用，調用端時間花費115ms，但是從arthas trace上看，spring mvc只消耗了18ms，那么剩下的97ms去哪了呢？
本地測試后已經可以排除spring mvc的問題了，最后也是唯一可能出問題的點就是tomcat
可是本人并不熟悉tomcat中的源碼，就連請求入口都不清楚，tomcat里需要trace的類都不好找。。。
不過沒關系，有神器Arthas，可以通過stack命令來反向查找調用路徑，以org.springframework.web.servlet.DispatcherServlet作為參數：
stack 輸出當前方法被調用的調用路徑很多時候我們都知道一個方法被執行，但這個方法被執行的路徑非常多，或者你根本就不知道這個方法是從那里被執行了，此時你需要的是 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)
從stack日志上可以很直觀的看出DispatchServlet的調用棧，那么這么長的路徑，該trace哪個類呢（這里跳過spring mvc中的過濾器的trace過程，實際排查的時候也trace了一遍，但這詭異的時間消耗不是由這里過濾器產生的）？
有一定經驗的老司機從名字上大概也能猜出來從哪里下手比較好，那就是org.apache.coyote.http11.Http11Processor.service，從名字上看，http1.1處理器，這可能是一個比較好的切入點。下面來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
日志里有一個129ms的耗時點（時間比沒開arthas的時候更長是因為arthas本身帶來的性能消耗，所以生產環境小心使用），這個就是要找的問題點。
打問題點找到了，那怎么定位是什么導致的問題呢，又如何解決呢？
繼續trace吧，細化到具體的代碼塊或者內容。trace由于性能考慮，不會展示所有的調用路徑，如果調用路徑過深，只有手動深入trace，原則就是trace耗時長的那個方法：
[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
一段無聊的手動深入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
發現了一個值得暫停思考的點：
+---[min=0.004452ms,max=34.479307ms,total=74.206249ms,count=31] org.apache.catalina.webresources.TomcatJarInputStream:getNextJarEntry() #117
這行代碼加載了31次，一共耗時74ms；從名字上看，應該是tomcat加載jar包時的耗時，那么是加載了31個jar包的耗時，還是加載了jar包內的某些資源31次耗時呢？
TomcatJarInputStream這個類源碼的注釋寫到：
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，獲取jar包內META-INF/，META-INF/MANIFEST的資源，這是一個子類，更多的功能在父類JarInputStream里。
其實看到這里大概也能猜到問題了，tomcat加載jar包內META-INF/，META-INF/MANIFEST的資源導致的耗時，至于為什么連續請求不會耗時，應該是tomcat的緩存機制（下面介紹源碼分析）不著急定位問題，試著通過Arthas最終定位問題細節，繼續手動深入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
#這里一共31個trace日志，刪減了剩下的
從方法名上看，還是加載資源之類的意思。都已經到jdk源碼了，這時候來看一下TomcatJarInputStream這個類的源碼:
/**
* 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;
}
這個createZipEntry有個name參數，從注釋上看，是jar/zip文件名，如果能得到文件名這種關鍵信息，就可以直接定位問題了；還是通過Arthas，使用watch命令，動態監測方法調用數據
1.watch方法執行數據觀測
讓你能方便的觀察到指定方法的調用情況。能觀察到的范圍為：返回值、拋出異常、入參，通過編寫 OGNL 表達式進行對應變量的查看。
watch 該方法的入參：
[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],
這下直接看到了具體加載的資源名，這么熟悉的名字：swagger-ui，一個國外的rest接口文檔工具，又有國內開發者基于swagger-ui做了一套spring mvc的集成工具，通過注解就可以自動生成swagger-ui需要的接口定義json文件，用起來還比較方便，就是侵入性較強。
刪除swagger的jar包后問題，詭異的70+ms就消失了：
<!--pom 里刪除這兩個引用，這兩個包時國內開發者封裝的，swagger-ui并沒有提供java spring-mvc的支持包，swagger只是一個瀏覽器端的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>
那么為什么swagger會導致請求耗時呢，為什么每次請求偶讀會加載swagger內部的靜態資源呢？
其實這是tomcat-embed的一個bug吧，下面詳細介紹一下該Bug
2.Tomcat embed Bug分析&解決
源碼分析過程實在太漫長，而且也不是本文的重點，所以就不介紹了， 下面直接介紹下分析結果，順便貼一張tomcat處理請求的核心類圖：
(1) 為什么每次請求會加載Jar包內的靜態資源
關鍵在于org.apache.catalina.mapper.Mapper#internalMapWrapper這個方法，該版本下處理請求的方式有問題，導致每次都校驗靜態資源。
(2) 為什么連續請求不會出現問題
因為Tomcat對于這種靜態資源的解析是有緩存的，優先從緩存查找，緩存過期后再重新解析。具體參考org.apache.catalina.webresources.Cache，默認過期時間ttl是5000ms。
(3) 為什么本地不會復現
其實確切的說，是通過spring-boot打包插件后不能復現。由于啟動方式的不同，tomcat使用了不同的類去處理靜態資源，所以沒問題。
(4) 如何解決
升級tomcat-embed版本即可。
當前出現Bug的版本為：
- spring-boot:2.0.2.RELEASE，內置的tomcat embed版本為8.5.31
- 升級tomcat embed版本至8.5.40+即可解決此問題，新版本已經修復了
3.通過替換springboot pom properties方式
如果項目是maven是繼承的springboot，即parent配置為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中直接覆蓋properties即可：
<properties>
<tomcat.version>8.5.40</tomcat.version>
</properties>
升級spring boot版本：springboot 2.1.0.RELEASE中的tomcat embed版本已經大于8.5.31了，所以直接將springboot升級至該版本及以上版本就可以解決此問題。
