大家好，我是烤鸭:

      记一次项目无法访问的事件和处理。由于某个模块每隔几天就会出现无法访问，目前的最简单粗暴的方法就是重启。

1. 现象

      项目内日志打印正常，经过dubbo的rpc服务和接口调用正常。http接口无法访问。提示nginx 502。
    

2. 原因猜想

       通常提示502 基本是项目本身原因。但是日志一直打印正常，很奇怪。
    

3. 逐一排除

    检查了nginx，配置映射没有问题。
    以及从服务器本身通过curl localhost:端口的方式调用接口，发现也是调用不通。
    猜想有没有可能是连接被占满，无法创建新的连接。
    查看服务器该端口的连接。

netstat -an |grep 项目端口 
netstat -an |grep 项目端口 |wc -l

 发现大量 close_wait，如图所示。这就是项目访问 502 的原因。

    查看所有的tcp 连接命令。

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}' 

   再就是查看日志发现大量的关于redis的warn日志。 io.lettuce.core.RedisConnectionException: Connection closed prematurely

[INFO] [lettuce-eventExecutorLoop-4-2] [2019-09-17 00:00:00,001]  info(106) | Reconnecting, last destination was /127.0.1.44:6380
[INFO] [lettuce-eventExecutorLoop-4-3] [2019-09-17 00:00:00,001]  info(106) | Reconnecting, last destination was /127.0.1.44:6380
[INFO] [lettuce-eventExecutorLoop-4-1] [2019-09-17 00:00:00,001]  info(106) | Reconnecting, last destination was /127.0.1.45:6379
[INFO] [lettuce-nioEventLoop-6-2] [2019-09-17 00:00:00,004]  info(106) | [channel=0xaaed8169, /127.0.1.47:21559 -> /127.0.1.44:6379, epid=0xd06cd] Closing channel because endpoint is already closed
[INFO] [lettuce-nioEventLoop-6-3] [2019-09-17 00:00:00,004]  info(106) | [channel=0x737b0658, /127.0.1.47:21560 -> /127.0.1.44:6379, epid=0xd06cf] Closing channel because endpoint is already closed
[WARN] [lettuce-nioEventLoop-6-2] [2019-09-17 00:00:00,004]  warn(146) | Cannot reconnect: io.lettuce.core.RedisConnectionException: Connection closed prematurely
io.lettuce.core.RedisConnectionException: Connection closed prematurelyat io.lettuce.core.PlainChannelInitializer$1.channelInactive(PlainChannelInitializer.java:80)at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245)at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231)at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:224)at io.netty.channel.DefaultChannelPipeline$HeadContext.channelInactive(DefaultChannelPipeline.java:1429)at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:245)at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:231)at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:947)at io.netty.channel.AbstractChannel$AbstractUnsafe$8.run(AbstractChannel.java:822)at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:404)at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)at java.lang.Thread.run(Thread.java:748)

猜测上面的连接过多无法释放可能是跟redis有关。解决redis警告。
我们项目采用的redis的jar是下面这个。

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId><version>2.0.5.RELEASE</version>
</dependency>

里面有两个数据源可以选择，默认是lettuce，改为使用jedis。修改为如下。

<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId><version>2.0.5.RELEASE</version><exclusions><exclusion><groupId>io.lettuce</groupId><artifactId>lettuce-core</artifactId></exclusion></exclusions>
</dependency>

改完确实没警告日志了，但是没几天，502问题又复现了。发现不是这个导致的 close_wait过多。
其实没关系，这只是一个警告，理论上不会影响什么。可以看github上的issue。

https://github.com/lettuce-io/lettuce-core/issues/861

4.  深度挖掘

当时并没有往OOM考虑，毕竟项目的rpc接口调用正常。

生产环境由于没权限是无法生成dump文件的，就在测试系统生成了一下，想看看日志中有没有线程死锁或者其他情况。

生成 dump 文件。

jmap -dump:file=/tmp/dump/heap.hprof [pid]

使用 JProfiler 分析 dump日志。

jprofiler 下载地址：

 链接: https://pan.baidu.com/s/1WXaMUC7mJ3dH_WMc2kpDag 提取码: dcec 

发现还是有点收获的。搜索 Out 关键字，发现了惊喜。也就解释了之前的现象。如图。

找到问题了，但是还没有找到问题的源头。所以又出现问题后让运维再次启动的时候加大了 jvm内存，启动命令添加 -Xms512m -Xmx2g 希望这次可以撑的多几天。启动后没多久让运维帮忙查看jvm内存情况，可以发现，没几个小时老年代的使用已经82%。

查看某进程的gc情况。

jmap -heap Pid

Attaching to process ID 9782, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.191-b12using thread-local object allocation.
Parallel GC with 4 thread(s)Heap Configuration:MinHeapFreeRatio         = 0MaxHeapFreeRatio         = 100MaxHeapSize              = 2147483648 (2048.0MB)NewSize                  = 715653120 (682.5MB)MaxNewSize               = 715653120 (682.5MB)OldSize                  = 1431830528 (1365.5MB)NewRatio                 = 2SurvivorRatio            = 8MetaspaceSize            = 21807104 (20.796875MB)CompressedClassSpaceSize = 1073741824 (1024.0MB)MaxMetaspaceSize         = 17592186044415 MBG1HeapRegionSize         = 0 (0.0MB)Heap Usage:
PS Young Generation
Eden Space:capacity = 603455488 (575.5MB)used     = 178326152 (170.06507110595703MB)free     = 425129336 (405.43492889404297MB)29.55083772475361% used
From Space:capacity = 57671680 (55.0MB)used     = 7215904 (6.881622314453125MB)free     = 50455776 (48.118377685546875MB)12.512040571732955% used
To Space:capacity = 54525952 (52.0MB)used     = 0 (0.0MB)free     = 54525952 (52.0MB)0.0% used
PS Old Generationcapacity = 1431830528 (1365.5MB)used     = 1177733640 (1123.1743240356445MB)free     = 254096888 (242.32567596435547MB)82.25370370088939% used43209 interned Strings occupying 4908648 bytes.

再去生产日志中搜索 'OutOfMemoryError' 附近的内容，定位原因。

两处地方：
    1.    activeMq像队列中推送的时候：ActiveMQSession.send
    2.    使用poi导出：org.apache.poi.POIXMLDocument.write
详细日志如下：

org.springframework.web.util.NestedServletException: Handler dispatch failed; nested exception is java.lang.OutOfMemoryError: Java heap spaceat org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1006)at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:925)at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:974)at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:877)at javax.servlet.http.HttpServlet.service(HttpServlet.java:661)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.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)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)
Caused by: java.lang.OutOfMemoryError: Java heap spaceat org.apache.activemq.util.ByteArrayOutputStream.checkCapacity(ByteArrayOutputStream.java:59)at org.apache.activemq.util.ByteArrayOutputStream.write(ByteArrayOutputStream.java:48)at java.io.DataOutputStream.write(DataOutputStream.java:107)at java.io.DataOutputStream.writeUTF(DataOutputStream.java:401)at java.io.DataOutputStream.writeUTF(DataOutputStream.java:323)at org.apache.activemq.util.MarshallingSupport.marshalPrimitiveMap(MarshallingSupport.java:62)at org.apache.activemq.command.ActiveMQMapMessage.storeContent(ActiveMQMapMessage.java:156)at org.apache.activemq.command.ActiveMQMapMessage.copy(ActiveMQMapMessage.java:121)at org.apache.activemq.command.ActiveMQMapMessage.copy(ActiveMQMapMessage.java:116)at org.apache.activemq.ActiveMQSession.send(ActiveMQSession.java:1949)
--at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)at com.etc.service.impl.SigningServiceImpl$$EnhancerBySpringCGLIB$$e7423006.executeSign(<generated>)at com.etc.controller.CarSignedController.executeSign(CarSignedController.java:246)at sun.reflect.GeneratedMethodAccessor295.invoke(Unknown Source)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:209)

2019-10-16 16:53:47,262 [http-nio-9010-exec-47] DEBUG o.s.w.s.m.m.a.RequestMappingHandlerMapping - Looking up handler method for path /highway/car-signed/querySignList
2019-10-16 16:53:47,273 [http-nio-9010-exec-9] ERROR o.a.c.c.C.[.[localhost].[/].[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 spaceat org.apache.activemq.util.ByteArrayOutputStream.checkCapacity(ByteArrayOutputStream.java:59)at org.apache.activemq.util.ByteArrayOutputStream.write(ByteArrayOutputStream.java:48)at java.io.DataOutputStream.write(DataOutputStream.java:107)at java.io.DataOutputStream.writeUTF(DataOutputStream.java:401)at java.io.DataOutputStream.writeUTF(DataOutputStream.java:323)at org.apache.activemq.util.MarshallingSupport.marshalPrimitiveMap(MarshallingSupport.java:62)at org.apache.activemq.command.ActiveMQMapMessage.storeContent(ActiveMQMapMessage.java:156)at org.apache.activemq.command.ActiveMQMapMessage.copy(ActiveMQMapMessage.java:121)at org.apache.activemq.command.ActiveMQMapMessage.copy(ActiveMQMapMessage.java:116)at org.apache.activemq.ActiveMQSession.send(ActiveMQSession.java:1949)at org.apache.activemq.ActiveMQMessageProducer.send(ActiveMQMessageProducer.java:288)at org.apache.activemq.ActiveMQMessageProducer.send(ActiveMQMessageProducer.java:223)at org.apache.activemq.ActiveMQMessageProducerSupport.send(ActiveMQMessageProducerSupport.java:241)at com.etc.util.MQProviderUtil.sendMq(MQProviderUtil.java:61)at com.etc.util.servlet.ZjSigned.sendImageToZg(ZjSigned.java:246)at com.etc.util.handler.ZjSignedHandler.signed(ZjSignedHandler.java:102)at com.etc.service.impl.SigningServiceImpl.executeSign(SigningServiceImpl.java:298)at com.etc.service.impl.SigningServiceImpl$$FastClassBySpringCGLIB$$8d7e3c5e.invoke(<generated>)at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:746)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)at org.springframework.transaction.interceptor.TransactionInterceptor$$Lambda$484/819196473.proceedWithInvocation(Unknown Source)at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:294)at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:98)at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:185)at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688)at com.etc.service.impl.SigningServiceImpl$$EnhancerBySpringCGLIB$$e7423006.executeSign(<generated>)at com.etc.controller.CarSignedController.executeSign(CarSignedController.java:246)at sun.reflect.GeneratedMethodAccessor295.invoke(Unknown Source)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:209)

5.    分析代码

既然找到问题了，就去分析下代码吧。

5.1     poi导出的伪代码如下:

List<CarSigned> carSignList = signingService.exportSignList(carSignedRequest);XSSFWorkbook workBook = new XSSFWorkbook();// 创建一个工作薄对象2007XSSFSheet xssfSheet = workBook.createSheet();String[] headers = {""};int rowIndex = 0;Row row = xssfSheet.createRow(rowIndex++);for (int i = 0; i < headers.length; i++) {row.createCell(i).setCellValue(headers[i]);}for (CarSigned carSignedListDto : carSignList) {row = xssfSheet.createRow(rowIndex++);// 车牌号row.createCell(1).setCellValue(carSignedListDto.getVehicleNo());}String date = new SimpleDateFormat("yyyy_MM_dd").format(new Date());String codefilename = "";String msie = "MSIE";String fileNames = "filename" + date + ".xlsx";String agent = request.getHeader("USER-AGENT");boolean flag = (null != agent && -1 != agent.indexOf(msie) || null != agent && -1 != agent.indexOf("Trident"));if (flag) {String name = java.net.URLEncoder.encode(fileNames, "UTF-8");// IEcodefilename = name;} else {// chrome,firefogcodefilename = fileNames;}response.setHeader("Content-Disposition","attachment;filename=" + new String(codefilename.getBytes("UTF-8"), "iso8859-1"));// 固定格式response.setContentType("application/ynd.ms-excel;charset=UTF-8");OutputStream out = response.getOutputStream();workBook.write(out);out.flush();out.close();

说实话，和正常的导出没什么区别，没看出有什么问题，导出的量不到10w，理论上也不会OOME。

5.2  activemq工具类伪代码

package com.xxx.util;import org.apache.activemq.ActiveMQConnectionFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import javax.jms.*;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;/*** mq 工具1* @author wu**/
public class MQProviderUtil {private static final Logger logger = LoggerFactory.getLogger(MQProviderUtil.class);public static void sendMq(Map<String, String> map,String user,String password,String brokerUrl,String topic) {// 连接Connection connection = null;// 会话 发送或者接收消息的线程Session session = null;// 消息的目的地Destination destination;// 消息生产者MessageProducer messageProducer;// 实例化连接工厂ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(user,password,brokerUrl);try {// 通过连接工厂获取连接connection = connectionFactory.createConnection();// 启动连接connection.start();// 创建sessionsession = connection.createSession(true, Session.AUTO_ACKNOWLEDGE);// 创建一个叫sendFile的消息队列destination = session.createQueue(topic);logger.info(" 创建一个叫"+topic+"的消息队列");// 创建消息生产者messageProducer = session.createProducer(destination);MapMessage mapMsg = session.createMapMessage();  Set <String> set = map.keySet();for(String key:set){String value = map.get(key);mapMsg.setString(key,value);}/*   mapMsg.setString("name", "李寻欢1");mapMsg.setBoolean("IsHero", true);mapMsg.setInt("age", 35);*///通过消息生产者发出消息messageProducer.send(mapMsg);session.commit();} catch (Exception e) {logger.info("activeMq消息队列异常");e.printStackTrace();} finally {if (connection != null) {try {connection.close();session.close();} catch (Exception e2) {e2.printStackTrace();}}}}public static void main(String[] args) throws InterruptedException {for (int i = 0; i < 3000; i++) {Map<String,String> map  =  new HashMap<>();map.put("id","123");sendMq(map,"admin","admin","tcp://127.0.0.1:61616","signed");}}
}

单独看这段代码也没有问题，运行main方法也能跑。
唯一有点问题的就是代码里每次调用mq的地方都是调用 MQProviderUtil.sendMq 方法。
理论上实例化连接工厂只需要在项目初始化的时候创建一次，但是他每次调用都会创建。猜测可能是调用过于频繁，导致工厂对象来不及回收导致的OOM。

activeMQ和springboot 组合使用的可以参考这篇文章:
https://segmentfault.com/a/1190000014108398

本地启动项目，模拟线上并发量 *2，实测没问题是来得及回收的，如图JVM 回收曲线交替执行正常。

总结：

由于不是我们项目组，他们一直说是导出导致的，业务人员同时导出量过大，由于后台生成的excel时候没有采用分页查询，导致OOM。一次导出的数据大概在10W左右，除非恶意访问，我觉得不是导出导致的OOM，或者说不是导出的产生的OOM，是导出的时候把这个OOM暴露出来了。
后来我又去activemq的机器查看了内存和cpu，一切正常。
activemq日志有时候会warn：但是问题不大

Channel was inactive for too (>30000) long: tcp://127.0.0.54:5820 | org.apache.activemq.broker.TransportConnection.Transport | ActiveMQ InactivityMonitor Worker

后来又查了mq的版本为 apache-activemq-5.13.1。2016年的版，官方写的多线程有可能是导致OOM的。跟我们这厂家也不太符合。

http://activemq.apache.org/how-to-deal-with-large-number-of-threads-in-clients.html

后来换了个导出的工具类，就没有OOM的问题了，好TM尴尬....真的是POI引起的OOM???

其实如果方便的话只要让运维下次启动的时候把OOM日志记录到文件就好了。这样分析起来就方便多了。现在没问题了，也没机会了。

-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=./oom.out