在本系列的最后一篇文章中，我将展示如何在JDK中使用本机JMX支持来实现一种通知机制，该机制可以在HEAP内存超过特定阈值时向侦听器发出警报。

正如我在上一篇文章中讨论的那样，这种方法是理想的，因为它是推式而不是拉式，不是侵入式的，并且对应用程序的计算需求最小。

这些是本文说明的解决方案的关键组件：

• MemoryWarningService：此组件充当侦听器，并向Memory MBean注册其自身以接收通知。 可以使用介于0到1之间的百分比形式的阈值（其中1为100％）进行配置
• MemoryThreadDumper：当通知MemoryWarningService HEAP使用量超过阈值并且其职责是将线程转储写入文件时，将调用此组件。
• MemoryWarningServiceConfigurator：此组件是MBean，它公开一种用于更改MemoryWarningService阈值的方法。

该解决方案还提供用于在测试应用程序时填充HEAP的MemoryHeapFiller类和用于引导Spring环境的MemTest类。

当应用程序运行时（使用MemoryHeapFiller设置），您可以在URL上触发JConsole：service：jmx：rmi：// localhost / jndi / rmi：// localhost：8888 / jemosJmxConnector以jemosAdmin / secure连接并更改阈值各种价值。

该代码不是用于生产的：它不健壮，缺少许多注释，并且写入线程转储的文件名是硬编码的。 但是，它代表了一个很好的起点。

该代码附在下面。 您将需要Maven来构建它。

下载Jemos-jmx-experiments-0.0.1-SNAPSHOT-project

我尝试了一个初始阈值为0.5的场景，将其更改为0.3，然后更改为0.8。 结果如下所示：

2011-08-15 21:53:21 ClassPathXmlApplicationContext [INFO] Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@a4a63d8: startup date [Mon Aug 15 21:53:21 BST 2011]; root of context hierarchy
2011-08-15 21:53:21 XmlBeanDefinitionReader [INFO] Loading XML bean definitions from class path resource [jemos-jmx-appCtx.xml]
2011-08-15 21:53:21 PropertyPlaceholderConfigurer [INFO] Loading properties file from class path resource [jemos-jmx.properties]
2011-08-15 21:53:21 PropertyPlaceholderConfigurer [INFO] Loading properties file from URL [file:/C:/Users/mtedone/.secure/jmxconnector-credentials.properties]
2011-08-15 21:53:21 ThreadPoolTaskScheduler [INFO] Initializing ExecutorService  'myScheduler'
2011-08-15 21:53:21 ClassPathXmlApplicationContext [INFO] Bean 'myScheduler' of type [class org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
2011-08-15 21:53:21 DefaultListableBeanFactory [INFO] Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@30296f76: defining beans [propertyConfigurer,loggerConfigurator,memoryWarningServiceConfigurator,memoryHeapFiller,memoryThreadDumper,org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,mbeanExporter,jemosJmxServer,rmiRegistry,clientConnector,memoryMxBean,memoryWarningService,org.springframework.scheduling.annotation.internalAsyncAnnotationProcessor,org.springframework.scheduling.annotation.internalScheduledAnnotationProcessor,myScheduler]; root of factory hierarchy
2011-08-15 21:53:21 AnnotationMBeanExporter [INFO] Registering beans for JMX exposure on startup
2011-08-15 21:53:21 RmiRegistryFactoryBean [INFO] Looking for RMI registry at port '8888'
2011-08-15 21:53:23 RmiRegistryFactoryBean [INFO] Could not detect RMI registry - creating new one
2011-08-15 21:53:23 ConnectorServerFactoryBean [INFO] JMX connector server started: javax.management.remote.rmi.RMIConnectorServer@4355d3a3
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'jemosJmxServer' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'loggerConfigurator' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Bean with name 'memoryWarningServiceConfigurator' has been autodetected for JMX exposure
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located managed bean 'loggerConfigurator': registering with JMX server as MBean [jemos.mbeans:type=config,name=LoggingConfiguration]
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located MBean 'jemosJmxServer': registering with JMX server as MBean [jemos.mbeans:name=jemosJmxServer,type=RMIConnectorServer]
2011-08-15 21:53:23 AnnotationMBeanExporter [INFO] Located managed bean 'memoryWarningServiceConfigurator': registering with JMX server as MBean [jemos.mbeans:type=config,name=MemoryWarningServiceConfiguration]
2011-08-15 21:53:23 MemoryWarningService [INFO] Percentage is: 0.5
2011-08-15 21:53:23 MemoryWarningService [INFO] Listener added to JMX bean
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
2011-08-15 21:53:37 MemoryWarningService [INFO] Percentage is: 0.3
2011-08-15 21:53:37 MemoryWarningServiceConfigurator [INFO] Memory threshold set to 0.3
Adding data...
2011-08-15 21:53:38 MemoryWarningService [WARN] Memory usage low!!!
2011-08-15 21:53:38 MemoryWarningService [WARN] percentageUsed = 0.3815679398794023
2011-08-15 21:53:38 MemoryThreadDumper [WARN] Stacks dumped to: C:/tmp/stacks.dump
Adding data...
Adding data...
Adding data...
2011-08-15 21:53:45 MemoryWarningService [INFO] Percentage is: 0.8
2011-08-15 21:53:45 MemoryWarningServiceConfigurator [INFO] Memory threshold set to 0.8
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
Adding data...
2011-08-15 21:54:01 MemoryWarningService [WARN] Memory usage low!!!
2011-08-15 21:54:01 MemoryWarningService [WARN] percentageUsed = 0.8383333266727508
2011-08-15 21:54:02 MemoryThreadDumper [WARN] Stacks dumped to: C:/tmp/stacks.dump
Adding data...
Adding data...
Adding data...
Exception in thread "JMX server connection timeout 24" java.lang.OutOfMemoryError: Java heap space

内存警告服务

package uk.co.jemos.experiments.jmx;import java.lang.management.ManagementFactory;
import java.lang.management.MemoryNotificationInfo;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryType;import javax.annotation.PostConstruct;
import javax.management.Notification;
import javax.management.NotificationEmitter;
import javax.management.NotificationListener;import org.springframework.beans.factory.annotation.Autowired;/*** A component which sends notifications when the HEAP memory is above a certain* threshold.* * @author mtedone* */
public class MemoryWarningService implements NotificationListener {/** This bean's name */public static final String MBEAN_NAME = "jemos.mbeans:type=monitoring,name=MemoryWarningService";/** The application logger */private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger.getLogger(MemoryWarningService.class);@Autowiredprivate NotificationEmitter memoryMxBean;@Autowiredprivate MemoryThreadDumper threadDumper;/** A pool of Memory MX Beans specialised in HEAP management */private static final MemoryPoolMXBean tenuredGenPool = findTenuredGenPool();/*** {@inheritDoc}*/@Overridepublic void handleNotification(Notification notification, Object handback) {if (notification.getType().equals(MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED)) {long maxMemory = tenuredGenPool.getUsage().getMax();long usedMemory = tenuredGenPool.getUsage().getUsed();LOG.warn("Memory usage low!!!");double percentageUsed = (double) usedMemory / maxMemory;LOG.warn("percentageUsed = " + percentageUsed);threadDumper.dumpStacks();} else {LOG.info("Other notification received..."+ notification.getMessage());}}/*** It sets the threshold percentage.* * @param percentage*/public void setPercentageUsageThreshold(double percentage) {if (percentage <= 0.0 || percentage > 1.0) {throw new IllegalArgumentException("Percentage not in range");} else {LOG.info("Percentage is: " + percentage);}long maxMemory = tenuredGenPool.getUsage().getMax();long warningThreshold = (long) (maxMemory * percentage);tenuredGenPool.setUsageThreshold(warningThreshold);}@PostConstructpublic void completeSetup() {memoryMxBean.addNotificationListener(this, null, null);LOG.info("Listener added to JMX bean");}/*** Tenured Space Pool can be determined by it being of type HEAP and by it* being possible to set the usage threshold.*/private static MemoryPoolMXBean findTenuredGenPool() {for (MemoryPoolMXBean pool : ManagementFactory.getMemoryPoolMXBeans()) {// I don't know whether this approach is better, or whether// we should rather check for the pool name "Tenured Gen"?if (pool.getType() == MemoryType.HEAP&& pool.isUsageThresholdSupported()) {return pool;}}throw new AssertionError("Could not find tenured space");}}

内存线程转储器

package uk.co.jemos.experiments.jmx;import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadInfo;
import java.lang.management.ThreadMXBean;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;import org.apache.commons.io.IOUtils;
import org.springframework.stereotype.Component;/*** This component dumps the thread stack to the file system.* * @author mtedone* */
@Component
public class MemoryThreadDumper {/** The application logger */private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger.getLogger(MemoryThreadDumper.class);/*** It dumps the Thread stacks* * @throws IOException*/public void dumpStacks() {// hard-coded: This needs to be changed to a property or somethingString stackFileName = "C:/tmp/stacks.dump";ThreadMXBean mxBean = ManagementFactory.getThreadMXBean();ThreadInfo[] threadInfos = mxBean.getThreadInfo(mxBean.getAllThreadIds(), 0);Map<Long, ThreadInfo> threadInfoMap = new HashMap<Long, ThreadInfo>();for (ThreadInfo threadInfo : threadInfos) {threadInfoMap.put(threadInfo.getThreadId(), threadInfo);}File dumpFile = new File(stackFileName);BufferedWriter writer = null;try {writer = new BufferedWriter(new FileWriter(dumpFile));this.dumpTraces(mxBean, threadInfoMap, writer);LOG.warn("Stacks dumped to: " + stackFileName);} catch (IOException e) {throw new IllegalStateException("An exception occurred while writing the thread dump");} finally {IOUtils.closeQuietly(writer);}}private void dumpTraces(ThreadMXBean mxBean,Map<Long, ThreadInfo> threadInfoMap, Writer writer)throws IOException {Map<Thread, StackTraceElement[]> stacks = Thread.getAllStackTraces();writer.write("Dump of "+ stacks.size()+ " thread at "+ new SimpleDateFormat("yyyy/MM/dd HH:mm:ss z").format(new Date(System.currentTimeMillis())) + "\n\n");for (Map.Entry<Thread, StackTraceElement[]> entry : stacks.entrySet()) {Thread thread = entry.getKey();writer.write("\"" + thread.getName() + "\" prio="+ thread.getPriority() + " tid=" + thread.getId() + " "+ thread.getState() + " "+ (thread.isDaemon() ? "deamon" : "worker") + "\n");ThreadInfo threadInfo = threadInfoMap.get(thread.getId());if (threadInfo != null) {writer.write("    native=" + threadInfo.isInNative()+ ", suspended=" + threadInfo.isSuspended()+ ", block=" + threadInfo.getBlockedCount() + ", wait="+ threadInfo.getWaitedCount() + "\n");writer.write("    lock=" + threadInfo.getLockName()+ " owned by " + threadInfo.getLockOwnerName() + " ("+ threadInfo.getLockOwnerId() + "), cpu="+ mxBean.getThreadCpuTime(threadInfo.getThreadId())/ 1000000L + ", user="+ mxBean.getThreadUserTime(threadInfo.getThreadId())/ 1000000L + "\n");}for (StackTraceElement element : entry.getValue()) {writer.write("        ");writer.write(element.toString());writer.write("\n");}writer.write("\n");}}}

内存服务配置MBean

package uk.co.jemos.experiments.jmx.mbeans;import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.jmx.export.annotation.ManagedOperation;
import org.springframework.jmx.export.annotation.ManagedOperationParameter;
import org.springframework.jmx.export.annotation.ManagedOperationParameters;
import org.springframework.jmx.export.annotation.ManagedResource;
import org.springframework.stereotype.Component;import uk.co.jemos.experiments.jmx.MemoryWarningService;@Component
@ManagedResource(objectName = MemoryWarningServiceConfigurator.MBEAN_NAME, //
description = "Allows clients to set the memory threshold")
public class MemoryWarningServiceConfigurator implementsApplicationContextAware {/** The application logger */private static final org.apache.log4j.Logger LOG = org.apache.log4j.Logger.getLogger(MemoryWarningServiceConfigurator.class);public static final String MBEAN_NAME = "jemos.mbeans:type=config,name=MemoryWarningServiceConfiguration";private ApplicationContext ctx;@ManagedOperation(description = "Sets the memory threshold for the memory warning system")@ManagedOperationParameters({ @ManagedOperationParameter(description = "The memory threshold", name = "memoryThreshold"), })public void setMemoryThreshold(double memoryThreshold) {MemoryWarningService memoryWarningService = (MemoryWarningService) ctx.getBean("memoryWarningService");memoryWarningService.setPercentageUsageThreshold(memoryThreshold);LOG.info("Memory threshold set to " + memoryThreshold);}@Overridepublic void setApplicationContext(ApplicationContext applicationContext)throws BeansException {ctx = applicationContext;}}

Spring配置

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"xmlns:util="http://www.springframework.org/schema/util"xmlns:task="http://www.springframework.org/schema/task"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsdhttp://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.0.xsdhttp://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.0.xsd"><bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"  ><property name="locations"><list><value>classpath:jemos-jmx.properties</value><value>file:///${user.home}/.secure/jmxconnector-credentials.properties</value></list></property></bean><context:component-scan base-package="uk.co.jemos.experiments.jmx" /><context:mbean-export default-domain="jemos.mbeans" /><bean id="jemosJmxServer" class="org.springframework.jmx.support.ConnectorServerFactoryBean"       depends-on="rmiRegistry"><property name="objectName" value="connector:name=rmi" /><property name="serviceUrl"value="service:jmx:rmi://localhost/jndi/rmi://localhost:${jemos.jmx.rmi.port}/jemosJmxConnector" /><property name="environment"><!-- the following is only valid when the sun jmx implementation is used --><map><entry key="jmx.remote.x.password.file" value="${user.home}/.secure/jmxremote.password" /><entry key="jmx.remote.x.access.file" value="${user.home}/.secure/jmxremote.access" /></map></property></bean><bean id="rmiRegistry" class="org.springframework.remoting.rmi.RmiRegistryFactoryBean"><property name="port" value="${jemos.jmx.rmi.port}" /></bean><bean id="clientConnector" class="org.springframework.jmx.support.MBeanServerConnectionFactoryBean"       depends-on="jemosJmxServer"><property name="serviceUrl"value="service:jmx:rmi://localhost/jndi/rmi://localhost:${jemos.jmx.rmi.port}/jemosJmxConnector" /><property name="environment"><map><entry key="jmx.remote.credentials"><beanfactory-method="commaDelimitedListToStringArray"><constructor-arg value="${jmx.username},${jmx.password}" /></bean></entry></map></property></bean><bean id="memoryMxBean" class="java.lang.management.ManagementFactory"factory-method="getMemoryMXBean" /><bean id="memoryWarningService" class="uk.co.jemos.experiments.jmx.MemoryWarningService"><property name="percentageUsageThreshold" value="0.5" /></bean><task:annotation-driven scheduler="myScheduler" />   <task:scheduler id="myScheduler" pool-size="10" />    </beans>

参考： JMX和Spring –我们的JCG合作伙伴 Marco Tedone的第3部分 ，位于Marco Tedone的博客博客中。