一. 上传我们需要实战模拟的Jar包到linux服务器
scp /Users/sunww/Desktop/demo-0.0.1-SNAPSHOT.jar root@10.50.15.60:/httx/packjar
二. 启动Jar包
java -jar demo-0.0.1-SNAPSHOT.jar
三. 前端发起请求
curl http://localhost:8080/admin/test?a=1
应用日志显示在循环打印数据：
此时本地电脑的风扇在拼命旋转，笔记本很烫。
四. 利用top命令查看
通过上面可以看到pid=5046这个进程占用cpu达到94%，所以这个进程出现问题了。
五. 利用top -p pid -H 查找该进程占用cpu高的线程信息
我们进一步通过下面的命令，可以查看5046进程里占用cpu高的线程，如下：
top -p 5046 -H
上图清楚的显示pid=5092这个线程占用cpu达到92%，走的是8080端口的http请求。
六.利用jstack锁定有问题的代码类
先将上面的pid=5092转化成16进制
printf "%x \n" 5092
方法一：直接通过grep命令查找13e4
然后用 jstack 5046 | grep 13e4 -A 30 查找问题代码【专门查找13e4这个线程信息】，如下图：
上图：可看出是HomeController类的第31行出现问题
方法二：输出5046所有信息后，ctrl + f 去查找13e4这个线程信息
我们也可以将5046这个进程信息全部打印出来，通过ctrl + f 去查找13e4这个线程信息，然后分析
[root@192 ~]# jstack 5046
2021-09-26 07:26:02
Full thread dump OpenJDK 64-Bit Server VM (25.242-b08 mixed mode):
"Attach Listener" #23 daemon prio=9 os_prio=0 tid=0x00007fa798001000 nid=0x1446 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"http-nio-8080-exec-1" #22 daemon prio=5 os_prio=0 tid=0x00007fa774030000 nid=0x13e4 runnable [0x00007fa7b019b000]
java.lang.Thread.State: RUNNABLE
at java.io.FileOutputStream.writeBytes(Native Method)
at java.io.FileOutputStream.write(FileOutputStream.java:326)
at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:82)
at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:140)
- locked <0x00000000e34422f8> (a java.io.BufferedOutputStream)
at java.io.PrintStream.write(PrintStream.java:482)
- locked <0x00000000e34422d8> (a java.io.PrintStream)
at sun.nio.cs.StreamEncoder.writeBytes(StreamEncoder.java:221)
at sun.nio.cs.StreamEncoder.implFlushBuffer(StreamEncoder.java:291)
at sun.nio.cs.StreamEncoder.flushBuffer(StreamEncoder.java:104)
- locked <0x00000000e3442418> (a java.io.OutputStreamWriter)
at java.io.OutputStreamWriter.flushBuffer(OutputStreamWriter.java:185)
at java.io.PrintStream.write(PrintStream.java:527)
- locked <0x00000000e34422d8> (a java.io.PrintStream)
at java.io.PrintStream.print(PrintStream.java:611)
at java.io.PrintStream.println(PrintStream.java:750)
- locked <0x00000000e34422d8> (a java.io.PrintStream)
at com.example.demo.HomeController.test(HomeController.java:31)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)
at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:133)
at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827)
at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738)
at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
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:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
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:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
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:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:798)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1434)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
- locked <0x00000000e45d7d70> (a org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Thread.java:748)
"DestroyJavaVM" #21 prio=5 os_prio=0 tid=0x00007fa7c004b800 nid=0x13b7 waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"http-nio-8080-AsyncTimeout" #19 daemon prio=5 os_prio=0 tid=0x00007fa7c1a98800 nid=0x13cc waiting on condition [0x00007fa7aa6f7000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.apache.coyote.AbstractProtocol$AsyncTimeout.run(AbstractProtocol.java:1138)
at java.lang.Thread.run(Thread.java:748)
"http-nio-8080-Acceptor-0" #18 daemon prio=5 os_prio=0 tid=0x00007fa7c0a28800 nid=0x13cb runnable [0x00007fa7aa7f8000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:419)
at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:247)
- locked <0x00000000e45f1b78> (a java.lang.Object)
at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:443)
at java.lang.Thread.run(Thread.java:748)
"http-nio-8080-ClientPoller-1" #17 daemon prio=5 os_prio=0 tid=0x00007fa7c0a26800 nid=0x13ca runnable [0x00007fa7aa8f9000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
- locked <0x00000000e45dc1e8> (a sun.nio.ch.Util$3)
- locked <0x00000000e45dc1d8> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000000e45dbfd0> (a sun.nio.ch.EPollSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:775)
at java.lang.Thread.run(Thread.java:748)
"http-nio-8080-ClientPoller-0" #16 daemon prio=5 os_prio=0 tid=0x00007fa7c0b93800 nid=0x13c9 runnable [0x00007fa7aa9fa000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
- locked <0x00000000e45f93b0> (a sun.nio.ch.Util$3)
- locked <0x00000000e45f93a0> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000000e45f9268> (a sun.nio.ch.EPollSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
at org.apache.tomcat.util.net.NioEndpoint$Poller.run(NioEndpoint.java:775)
at java.lang.Thread.run(Thread.java:748)
"NioBlockingSelector.BlockPoller-1" #15 daemon prio=5 os_prio=0 tid=0x00007fa7c129e800 nid=0x13c8 runnable [0x00007fa7aaafb000]
java.lang.Thread.State: RUNNABLE
at sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
at sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
at sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:93)
at sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
- locked <0x00000000e45d64f0> (a sun.nio.ch.Util$3)
- locked <0x00000000e45d64e0> (a java.util.Collections$UnmodifiableSet)
- locked <0x00000000e45d63a8> (a sun.nio.ch.EPollSelectorImpl)
at sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
at org.apache.tomcat.util.net.NioBlockingSelector$BlockPoller.run(NioBlockingSelector.java:339)
"container-0" #14 prio=5 os_prio=0 tid=0x00007fa7c1997000 nid=0x13c7 waiting on condition [0x00007fa7aadfc000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.apache.catalina.core.StandardServer.await(StandardServer.java:427)
at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainer$1.run(TomcatEmbeddedServletContainer.java:174)
"ContainerBackgroundProcessor[StandardEngine[Tomcat]]" #13 daemon prio=5 os_prio=0 tid=0x00007fa7c0a15000 nid=0x13c6 waiting on condition [0x00007fa7aaefd000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.apache.catalina.core.ContainerBase$ContainerBackgroundProcessor.run(ContainerBase.java:1355)
at java.lang.Thread.run(Thread.java:748)
"Service Thread" #7 daemon prio=9 os_prio=0 tid=0x00007fa7c01ad000 nid=0x13c0 runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C1 CompilerThread1" #6 daemon prio=9 os_prio=0 tid=0x00007fa7c01a2800 nid=0x13bf waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"C2 CompilerThread0" #5 daemon prio=9 os_prio=0 tid=0x00007fa7c0193000 nid=0x13be waiting on condition [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Signal Dispatcher" #4 daemon prio=9 os_prio=0 tid=0x00007fa7c0191000 nid=0x13bd runnable [0x0000000000000000]
java.lang.Thread.State: RUNNABLE
"Finalizer" #3 daemon prio=8 os_prio=0 tid=0x00007fa7c0166800 nid=0x13bc in Object.wait() [0x00007fa7b0ffe000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000000e35cbd10> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
- locked <0x00000000e35cbd10> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)
"Reference Handler" #2 daemon prio=10 os_prio=0 tid=0x00007fa7c0162000 nid=0x13bb in Object.wait() [0x00007fa7c4105000]
java.lang.Thread.State: WAITING (on object monitor)
at java.lang.Object.wait(Native Method)
- waiting on <0x00000000e35cb908> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:502)
at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
- locked <0x00000000e35cb908> (a java.lang.ref.Reference$Lock)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
"VM Thread" os_prio=0 tid=0x00007fa7c0158000 nid=0x13ba runnable
"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x00007fa7c005e000 nid=0x13b8 runnable
"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x00007fa7c0060000 nid=0x13b9 runnable
"VM Periodic Task Thread" os_prio=0 tid=0x00007fa7c01af800 nid=0x13c1 waiting on condition
JNI global references: 246七. 修改问题代码
通过上面可以锁定HomeController类的println方法（System.out.println）有问题，查看代码确实这里有个死循环打印的问题，修改代码后问题解决。
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