使用Arthas神器，定位解決SpringBoot接口超時(shí)問(wèn)題（附診斷流程）

背景

公司有個(gè)渠道系統(tǒng)，專門對(duì)接三方渠道使用，沒(méi)有什么業(yè)務(wù)邏輯，主要是轉(zhuǎn)換報(bào)文和參數(shù)校驗(yàn)之類的工作，起著一個(gè)承上啟下的作用。

最近在優(yōu)化接口的響應(yīng)時(shí)間，優(yōu)化了代碼之后，但是時(shí)間還是達(dá)不到要求；有一個(gè)詭異的100ms左右的耗時(shí)問(wèn)題，在接口中打印了請(qǐng)求處理時(shí)間后，和調(diào)用方的響應(yīng)時(shí)間還有差了100ms左右。比如程序里記錄150ms，但是調(diào)用方等待時(shí)間卻為250ms左右。

下面記錄下當(dāng)時(shí)詳細(xì)的定位&解決流程（其實(shí)解決很簡(jiǎn)單，關(guān)鍵在于怎么定位并找到解決問(wèn)題的方法）

定位過(guò)程

分析代碼

渠道系統(tǒng)是一個(gè)常見(jiàn)的spring-boot web工程，使用了集成的tomcat。分析了代碼之后，發(fā)現(xiàn)并沒(méi)有特殊的地方，沒(méi)有特殊的過(guò)濾器或者攔截器，所以初步排除是業(yè)務(wù)代碼問(wèn)題

分析調(diào)用流程

出現(xiàn)這個(gè)問(wèn)題之后，首先確認(rèn)了下接口的調(diào)用流程。由于是內(nèi)部測(cè)試，所以調(diào)用流程較少。

Nginx -反向代理-> 渠道系統(tǒng)

公司是云服務(wù)器，網(wǎng)絡(luò)走的也是云的內(nèi)網(wǎng)。由于不明確問(wèn)題的原因，所以用排除法，首先確認(rèn)服務(wù)器網(wǎng)絡(luò)是否有問(wèn)題。

先確認(rèn)發(fā)送端到Nginx Host是否有問(wèn)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(jié)果上看，發(fā)送端到Nginx主機(jī)的延遲是無(wú)問(wèn)題的，接下來(lái)查看Nginx到渠道系統(tǒng)的網(wǎng)絡(luò)。

#?由于日志是沒(méi)問(wèn)題的，這里直接復(fù)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(jié)果上看，Nginx到渠道系統(tǒng)服務(wù)器網(wǎng)絡(luò)延遲也是沒(méi)問(wèn)題的

既然網(wǎng)絡(luò)看似沒(méi)問(wèn)題，那么可以繼續(xù)排除法，砍掉Nginx，客戶端直接再渠道系統(tǒng)的服務(wù)器上，通過(guò)回環(huán)地址（localhost）直連，避免經(jīng)過(guò)網(wǎng)卡/dns，縮小問(wèn)題范圍看看能否復(fù)現(xiàn)（這個(gè)應(yīng)用和地址是我后期模擬的，測(cè)試的是一個(gè)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(qǐng)求總耗時(shí)

從curl日志上看，通過(guò)回環(huán)地址調(diào)用一個(gè)空接口耗時(shí)也有73ms。這就奇怪了，跳過(guò)了中間所有調(diào)用節(jié)點(diǎn)（包括過(guò)濾器&攔截器之類），直接請(qǐng)求應(yīng)用一個(gè)空接口，都有73ms的耗時(shí)，再請(qǐng)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(qǐng)求耗時(shí)就正常了，變成了3ms。經(jīng)查閱資料，linux curl是默認(rèn)開(kāi)啟http keep-alive的。就算不開(kāi)啟keep-alive，每次重新handshake，也不至于需要70ms。

經(jīng)過(guò)不斷分析測(cè)試發(fā)現(xiàn)，連續(xù)請(qǐng)求的話時(shí)間就會(huì)很短，每次請(qǐng)求只需要幾毫秒，但是如果隔一段時(shí)間再請(qǐng)求，就會(huì)花費(fèi)70ms以上。

從這個(gè)現(xiàn)象猜想，可能是某些緩存機(jī)制導(dǎo)致的，連續(xù)請(qǐng)求因?yàn)橛芯彺妫运俣瓤欤瑫r(shí)間長(zhǎng)緩存失效后導(dǎo)致時(shí)間長(zhǎng)。

那么這個(gè)問(wèn)題點(diǎn)到底在哪一層呢？tomcat層還是spring-webmvc呢？

光猜想定位不了問(wèn)題，還是得實(shí)際測(cè)試一下，把渠道系統(tǒng)的代碼放到本地ide里啟動(dòng)測(cè)試能否復(fù)現(xiàn)

但是導(dǎo)入本地Ide后，在Ide中啟動(dòng)后并不能復(fù)現(xiàn)問(wèn)題，并沒(méi)有70+ms的延遲問(wèn)題。這下頭疼了，本地?zé)o法復(fù)現(xiàn)，不能Debug，由于問(wèn)題點(diǎn)不在業(yè)務(wù)代碼，也不能通過(guò)加日志的方式來(lái)Debug

這時(shí)候可以祭出神器Arthas了

Arthas分析問(wèn)題

Arthas 是Alibaba開(kāi)源的Java診斷工具，深受開(kāi)發(fā)者喜愛(ài)。當(dāng)你遇到以下類似問(wèn)題而束手無(wú)策時(shí)，Arthas可以幫助你解決：

• 這個(gè)類從哪個(gè) jar 包加載的？為什么會(huì)報(bào)各種類相關(guān)的 Exception？
• 我改的代碼為什么沒(méi)有執(zhí)行到？難道是我沒(méi) commit？分支搞錯(cuò)了？
• 遇到問(wèn)題無(wú)法在線上 debug，難道只能通過(guò)加日志再重新發(fā)布嗎？
• 線上遇到某個(gè)用戶的數(shù)據(jù)處理有問(wèn)題，但線上同樣無(wú)法 debug，線下無(wú)法重現(xiàn)！
• 是否有一個(gè)全局視角來(lái)查看系統(tǒng)的運(yùn)行狀況？
• 有什么辦法可以監(jiān)控到JVM的實(shí)時(shí)運(yùn)行狀態(tài)？

上面是Arthas的官方簡(jiǎn)介，這次我只需要用他的一個(gè)小功能trace。動(dòng)態(tài)計(jì)算方法調(diào)用路徑和時(shí)間，這樣我就可以定位時(shí)間在哪個(gè)地方被消耗了。

• trace 方法內(nèi)部調(diào)用路徑，并輸出方法路徑上的每個(gè)節(jié)點(diǎn)上耗時(shí)
• trace 命令能主動(dòng)搜索 class-pattern／method-pattern
• 對(duì)應(yīng)的方法調(diào)用路徑，渲染和統(tǒng)計(jì)整個(gè)調(diào)用鏈路上的所有性能開(kāi)銷和追蹤調(diào)用鏈路。

有了神器，那么該追蹤什么方法呢？由于我對(duì)Tomcat源碼不是很熟，所以只能從spring mvc下手，先來(lái)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:()?#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:()?#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(diào)用，調(diào)用端時(shí)間花費(fèi)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(cè)試后已經(jīng)可以排除spring mvc的問(wèn)題了，最后也是唯一可能出問(wèn)題的點(diǎn)就是tomcat

可是本人并不熟悉tomcat中的源碼，就連請(qǐng)求入口都不清楚，tomcat里需要trace的類都不好找。。。

不過(guò)沒(méi)關(guān)系，有神器Arthas，可以通過(guò)stack命令來(lái)反向查找調(diào)用路徑，以org.springframework.web.servlet.DispatcherServlet作為參數(shù)：

stack 輸出當(dāng)前方法被調(diào)用的調(diào)用路徑

很多時(shí)候我們都知道一個(gè)方法被執(zhí)行，但這個(gè)方法被執(zhí)行的路徑非常多，或者你根本就不知道這個(gè)方法是從那里被執(zhí)行了，此時(shí)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
[email protected]()
????????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(diào)用棧，那么這么長(zhǎng)的路徑，該trace哪個(gè)類呢（這里跳過(guò)spring mvc中的過(guò)濾器的trace過(guò)程，實(shí)際排查的時(shí)候也trace了一遍，但這詭異的時(shí)間消耗不是由這里過(guò)濾器產(chǎn)生的）？

有一定經(jīng)驗(yàn)的老司機(jī)從名字上大概也能猜出來(lái)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(gè)比較好的切入點(diǎn)。下面來(lái)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(gè)129ms的耗時(shí)點(diǎn)（時(shí)間比沒(méi)開(kāi)arthas的時(shí)候更長(zhǎng)是因?yàn)閍rthas本身帶來(lái)的性能消耗，所以生產(chǎn)環(huán)境小心使用），這個(gè)就是要找的問(wèn)題點(diǎn)。

打問(wèn)題點(diǎn)找到了，那怎么定位是什么導(dǎo)致的問(wèn)題呢，又如何解決呢？

繼續(xù)trace吧，細(xì)化到具體的代碼塊或者內(nèi)容。trace由于性能考慮，不會(huì)展示所有的調(diào)用路徑，如果調(diào)用路徑過(guò)深，只有手動(dòng)深入trace，原則就是trace耗時(shí)長(zhǎng)的那個(gè)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:()?#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:()?#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(wú)聊的手動(dòng)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:()?#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:()?#113
????????+---[min=0.001175ms,max=0.001176ms,total=0.002351ms,count=2]?java.lang.Integer:()?#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(fā)現(xiàn)了一個(gè)值得暫停思考的點(diǎn)：

+---[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(shí)74ms；從名字上看，應(yīng)該是tomcat加載jar包時(shí)的耗時(shí)，那么是加載了31個(gè)jar包的耗時(shí)，還是加載了jar包內(nèi)的某些資源31次耗時(shí)呢？

TomcatJarInputStream這個(gè)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(nèi)META-INF/，META-INF/MANIFEST的資源，這是一個(gè)子類，更多的功能在父類JarInputStream里。

其實(shí)看到這里大概也能猜到問(wèn)題了，tomcat加載jar包內(nèi)META-INF/，META-INF/MANIFEST的資源導(dǎo)致的耗時(shí)，至于為什么連續(xù)請(qǐng)求不會(huì)耗時(shí)，應(yīng)該是tomcat的緩存機(jī)制（下面介紹源碼分析）

不著急定位問(wèn)題，試著通過(guò)Arthas最終定位問(wèn)題細(xì)節(jié)，繼續(xù)手動(dòng)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(gè)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(jīng)到j(luò)dk源碼了，這時(shí)候來(lái)看一下TomcatJarInputStream這個(gè)類的源碼:

/**
?*?Creates?a?new?JarEntry?(ZipEntry)?for?the
?*?specified?JAR?file?entry?name.?The?manifest?attributes?of
?*?the?specified?JAR?file?entry?name?will?be?copied?to?the?new
?*?JarEntry.
?*
?*?@param?name?the?name?of?the?JAR/ZIP?file?entry
?*?@return?the?JarEntry?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(gè)createZipEntry有個(gè)name參數(shù)，從注釋上看，是jar/zip文件名，如果能得到文件名這種關(guān)鍵信息，就可以直接定位問(wèn)題了；還是通過(guò)Arthas，使用watch命令，動(dòng)態(tài)監(jiān)測(cè)方法調(diào)用數(shù)據(jù)

watch方法執(zhí)行數(shù)據(jù)觀測(cè)

讓你能方便的觀察到指定方法的調(diào)用情況。能觀察到的范圍為：返回值、拋出異常、入?yún)ⅲㄟ^(guò)編寫 OGNL 表達(dá)式進(jìn)行對(duì)應(yīng)變量的查看。

watch 該方法的入?yún)?/p>

[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(gè)國(guó)外的rest接口文檔工具，又有國(guó)內(nèi)開(kāi)發(fā)者基于swagger-ui做了一套spring mvc的集成工具，通過(guò)注解就可以自動(dòng)生成swagger-ui需要的接口定義json文件，用起來(lái)還比較方便，就是侵入性較強(qiáng)。

刪除swagger的jar包后問(wèn)題，詭異的70+ms就消失了

<dependency>
????<groupId>io.springfoxgroupId>
????<artifactId>springfox-swagger2artifactId>
????<version>2.9.2version>
dependency>
<dependency>
????<groupId>io.springfoxgroupId>
????<artifactId>springfox-swagger-uiartifactId>
????<version>2.9.2version>
dependency>

那么為什么swagger會(huì)導(dǎo)致請(qǐng)求耗時(shí)呢，為什么每次請(qǐng)求偶讀會(huì)加載swagger內(nèi)部的靜態(tài)資源呢？

其實(shí)這是tomcat-embed的一個(gè)bug吧，下面詳細(xì)介紹一下該Bug

Tomcat embed Bug分析&解決

源碼分析過(guò)程實(shí)在太漫長(zhǎng)，而且也不是本文的重點(diǎn)，所以就不介紹了， 下面直接介紹下分析結(jié)果

順便貼一張tomcat處理請(qǐng)求的核心類圖

為什么每次請(qǐng)求會(huì)加載Jar包內(nèi)的靜態(tài)資源

關(guān)鍵在于org.apache.catalina.mapper.Mapper#internalMapWrapper這個(gè)方法，該版本下處理請(qǐng)求的方式有問(wèn)題，導(dǎo)致每次都校驗(yàn)靜態(tài)資源。

為什么連續(xù)請(qǐng)求不會(huì)出現(xiàn)問(wèn)題

因?yàn)門omcat對(duì)于這種靜態(tài)資源的解析是有緩存的，優(yōu)先從緩存查找，緩存過(guò)期后再重新解析。具體參考org.apache.catalina.webresources.Cache，默認(rèn)過(guò)期時(shí)間ttl是5000ms。

為什么本地不會(huì)復(fù)現(xiàn)

其實(shí)確切的說(shuō)，是通過(guò)spring-boot打包插件后不能復(fù)現(xiàn)。由于啟動(dòng)方式的不同，tomcat使用了不同的類去處理靜態(tài)資源，所以沒(méi)問(wèn)題

如何解決

升級(jí)tomcat-embed版本即可

當(dāng)前出現(xiàn)Bug的版本為：

spring-boot:2.0.2.RELEASE，內(nèi)置的tomcat embed版本為8.5.31

升級(jí)tomcat embed版本至8.5.40+即可解決此問(wèn)題，新版本已經(jīng)修復(fù)了

通過(guò)替換springboot pom properties方式

如果項(xiàng)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.bootgroupId>
????????<artifactId>spring-boot-starter-parentartifactId>
????????<version>2.0.2.RELEASEversion>
????????<relativePath/>?
????parent>

pom中直接覆蓋properties即可：

<properties>
????<tomcat.version>8.5.40tomcat.version>
properties>

升級(jí)spring boot版本

springboot 2.1.0.RELEASE中的tomcat embed版本已經(jīng)大于8.5.31了，所以直接將springboot升級(jí)至該版本及以上版本就可以解決此問(wèn)題

END