來源：segmentfault.com/a/1190000020383866
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，主要是轉換報文和引數校驗之類的作業，起著一個承上啟下的作用，
最近在優化介面的回應時間，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，在介面中列印了請求處理時間后，和呼叫方的回應時間還有差了100ms左右，比如程式里記錄150ms，但是呼叫方等待時間卻為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）
定位程序
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
分析呼叫流程
出現這個問題之后，首先確認了下介面的呼叫流程，由于是內部測驗，所以呼叫流程較少，
Nginx -反向代理-> 渠道系統
公司是云服務器，網路走的也是云的內網，由于不明確問題的原因，所以用排除法，首先確認服務器網路是否有問題，
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到渠道系統的網路，
# 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路延遲也是沒問題的
既然網路看似沒問題，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，測驗的是一個空介面）：
[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，通過回環地址呼叫一個空介面耗時也有73ms，這就奇怪了，跳過了中間所有呼叫節點（包括過濾器&攔截器之類），直接請求應用一個空介面，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，
經過不斷分析測驗發現，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，可能是某些快取機制導致的，連續請求因為有快取，所以速度快，時間長快取失效后導致時間長，
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，還是得實際測驗一下，把渠道系統的代碼放到本地ide里啟動測驗能否復現
但是匯入本地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
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資料處理有問題，但線上同樣無法 debug，線下無法重現！
- 是否有一個全域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，動態計算方法呼叫路徑和時間，這樣我就可以定位時間在哪個地方被消耗了，
- trace 方法內部呼叫路徑，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 - 對應的方法呼叫路徑，渲染和統計整個呼叫鏈路上的所有性能開銷和追蹤呼叫鏈路，
有了神器，那么該追蹤什么方法呢？由于我對Tomcat原始碼不是很熟，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
本次呼叫，呼叫端時間花費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？
本地測驗后已經可以排除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中的原始碼，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命令來反向查找呼叫路徑，以org.springframework.web.servlet.DispatcherServlet作為引數：
stack 輸出當前方法被呼叫的呼叫路徑
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的呼叫堆疊，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程序，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，不會展示所有的呼叫路徑，如果呼叫路徑過深，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這個類原始碼的注釋寫到：
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的快取機制（下面介紹原始碼分析）
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原始碼了，這時候來看一下TomcatJarInputStream這個類的原始碼:
/**
* 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引數，從注釋上看，是jar/zip檔案名，如果能得到檔案名這種關鍵資訊，就可以直接定位問題了；還是通過Arthas，使用watch命令，動態監測方法呼叫資料
watch方法執行資料觀測
讓你能方便的觀察到指定方法的呼叫情況，能觀察到的范圍為：回傳值、拋出例外、入參，通過撰寫 OGNL 運算式進行對應變數的查看，
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介面檔案工具，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需要的介面定義json檔案，用起來還比較方便，就是侵入性較強，
洗掉swagger的jar包后問題，詭異的70+ms就消失了
<!--pom 里洗掉這兩個參考，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
Tomcat embed Bug分析&解決
原始碼分析程序實在太漫長，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
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，
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決議是有快取的，優先從快取查找，快取過期后再重新決議，具體參考org.apache.catalina.webresources.Cache，默認過期時間ttl是5000ms，
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
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
通過替換springboot pom properties方式
如果專案是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中直接覆寫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，
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