JVM——OOM处理

一次OOM产生和分析演示：

1. IEDA配置

-Xmx30M -Xms30M -Xmn10M -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=D:\tmp\finance-collection-heapdump.hprof

在OOM的时候dump出文件，平时一定记得配置-XX:+HeapDumpPath地址，这样在线上服务发生OOM时才能依据文件进行分析。

2. 演示代码：

public void createOrderList(){
        List<Order> list = new ArrayList<>();
        while(true){
            Order order = new Order();
            List<Order> orders = Arrays.asList(order);
            list.addAll(orders);
            System.out.println("打印");
        }
    }

一段时间后报出OOM异常并在设置地址生成.hprof文件。

2022-04-10 08:29:30.851 ERROR 37656 --- [nio-8180-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: Java heap space] with root cause

java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:3210) ~[na:1.8.0_91]
	at java.util.Arrays.copyOf(Arrays.java:3181) ~[na:1.8.0_91]
	at java.util.ArrayList.grow(ArrayList.java:261) ~[na:1.8.0_91]
	at java.util.ArrayList.ensureExplicitCapacity(ArrayList.java:235) ~[na:1.8.0_91]
	at java.util.ArrayList.ensureCapacityInternal(ArrayList.java:227) ~[na:1.8.0_91]
	at java.util.ArrayList.addAll(ArrayList.java:579) ~[na:1.8.0_91]
	at io.seata.sample.controller.OrderController.createOrderList(OrderController.java:38) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_91]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_91]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_91]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_91]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:104) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:892) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1039) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.21.jar:9.0.21]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.21.jar:9.0.21]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:109) ~[spring-web-5.1.8.RELEASE.jar:5.1.8.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.21.jar:9.0.21]

生成文件：

3.使用VisualVM分析

导入生成的dump文件，选中排名靠前的可能出现问题的类，右键选择在实例视图中展示：

 在这里能根据引用找到该类的GCRoot(如果没有JVM的基础知识，可以简单理解为该类引用的源头)，选中GCRoot右键在线程中展示：

 最终定位到问题代码的位置：

说明： 这里演示的是最简单的一种情况，一次就能定位到是Order类出现问题，现实中不可能这么简单，会结合最近一次上线的功能，当前的QPS等进行分析，但是解决问题的流程是一样的。

参考：

【IT老齐043】IT老齐线上Java OOM排查与解决过程分享（下）_哔哩哔哩_bilibili

JVM——OOM处理_chenkaibsw的博客-优快云博客

OOM怎么办，教你生成dump文件以及查看 - 掘金