1. 概述

对 java 来说，jvm 的监控是工程应用中十分重要的一环，无论是日常的性能优化还是异常处理都离不开监控数据的分析。
java 的 java.lang.management 包提供了用于监控和管理 java 虚拟机及虚拟机各项指标的接口。

2. java.lang.management 提供的接口

java.lang.management 提供了下列接口。

java.lang.management 提供的接口

3. 应用实例

import java.lang.management.ClassLoadingMXBean;
import java.lang.management.CompilationMXBean;
import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryMXBean;
import java.lang.management.MemoryManagerMXBean;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryUsage;
import java.lang.management.OperatingSystemMXBean;
import java.lang.management.RuntimeMXBean;
import java.lang.management.ThreadMXBean;
import java.util.List;

import javax.management.MBeanServerConnection;

public class MBeanDemo {

    public static void main(String[] args) {
        showJvmInfo();
        showMemoryInfo();
        showSystem();
        showClassLoading();
        showCompilation();
        showThread();
        showGarbageCollector();
        showMemoryManager();
        showMemoryPool();
    }

    /**
     * Java 虚拟机的运行时系统
     */
    public static void showJvmInfo() {
        RuntimeMXBean mxbean = ManagementFactory.getRuntimeMXBean();
        String vendor = mxbean.getVmVendor();
        System.out.println("jvm name:" + mxbean.getVmName());
        System.out.println("jvm version:" + mxbean.getVmVersion());
        System.out.println("jvm bootClassPath:" + mxbean.getBootClassPath());
        System.out.println("jvm start time:" + mxbean.getStartTime());
    }

    /**
     * Java 虚拟机的内存系统
     */
    public static void showMemoryInfo() {
        MemoryMXBean mem = ManagementFactory.getMemoryMXBean();
        MemoryUsage heap = mem.getHeapMemoryUsage();
        System.out.println("Heap committed:" + heap.getCommitted() + " init:" + heap.getInit() + " max:"
                + heap.getMax() + " used:" + heap.getUsed());
    }

    /**
     * Java 虚拟机在其上运行的操作系统
     */
    public static void showSystem() {
        OperatingSystemMXBean op = ManagementFactory.getOperatingSystemMXBean();
        System.out.println("Architecture: " + op.getArch());
        System.out.println("Processors: " + op.getAvailableProcessors());
        System.out.println("System name: " + op.getName());
        System.out.println("System version: " + op.getVersion());
        System.out.println("Last minute load: " + op.getSystemLoadAverage());
    }

    /**
     * Java 虚拟机的类加载系统
     */
    public static void showClassLoading(){
        ClassLoadingMXBean cl = ManagementFactory.getClassLoadingMXBean();
        System.out.println("TotalLoadedClassCount: " + cl.getTotalLoadedClassCount());
        System.out.println("LoadedClassCount" + cl.getLoadedClassCount());
        System.out.println("UnloadedClassCount:" + cl.getUnloadedClassCount());
    }

    /**
     * Java 虚拟机的编译系统
     */
    public static void showCompilation(){
        CompilationMXBean com = ManagementFactory.getCompilationMXBean();
        System.out.println("TotalCompilationTime:" + com.getTotalCompilationTime());
        System.out.println("name:" + com.getName());
    }

    /**
     * Java 虚拟机的线程系统
     */
    public static void showThread(){
        ThreadMXBean thread = ManagementFactory.getThreadMXBean();
        System.out.println("ThreadCount" + thread.getThreadCount());
        System.out.println("AllThreadIds:" + thread.getAllThreadIds());
        System.out.println("CurrentThreadUserTime" + thread.getCurrentThreadUserTime());
        //......还有其他很多信息
    }

    /**
     * Java 虚拟机中的垃圾回收器。
     */
    public static void showGarbageCollector(){
        List<GarbageCollectorMXBean> gc = ManagementFactory.getGarbageCollectorMXBeans();
        HashSet younggcAlgorithm = new HashSet() {
            {
                this.add("Copy");
                this.add("ParNew");
                this.add("PS Scavenge");
            }
        };
        HashSet oldgcAlgorithm = new HashSet() {
            {
                this.add("MarkSweepCompact");
                this.add("PS MarkSweep");
                this.add("ConcurrentMarkSweep");
            }
        };
        for(GarbageCollectorMXBean GarbageCollectorMXBean : gc){
            String gcAlgorithm = GarbageCollectorMXBean.getName();
            System.out.println("name:" + gcAlgorithm);
            System.out.println("CollectionCount:" + GarbageCollectorMXBean.getCollectionCount());
            System.out.println("CollectionTime" + GarbageCollectorMXBean.getCollectionTime());
            if(younggcAlgorithm.contains(gcAlgorithm)) {
                System.out.println("YoungGCCount:" + GarbageCollectorMXBean.getCollectionCount());
                System.out.println("YoungGCTime" + GarbageCollectorMXBean.getCollectionTime());
            } else if(oldgcAlgorithm.contains(gcAlgorithm)) {
                System.out.println("FullGCCount:" + GarbageCollectorMXBean.getCollectionCount());
                System.out.println("FullGCTime" + GarbageCollectorMXBean.getCollectionTime());
            }
        }
    }

    /**
     * Java 虚拟机中的内存管理器
     */
    public static void showMemoryManager(){
        List<MemoryManagerMXBean> mm = ManagementFactory.getMemoryManagerMXBeans();
        for(MemoryManagerMXBean eachmm: mm){
            System.out.println("name:" + eachmm.getName());
            System.out.println("MemoryPoolNames:" + eachmm.getMemoryPoolNames().toString());
        }
    }

    /**
     * Java 虚拟机中的内存池
     */
    public static void showMemoryPool(){
        List<MemoryPoolMXBean> mps = ManagementFactory.getMemoryPoolMXBeans();
        for(MemoryPoolMXBean mp : mps){
            System.out.println("name:" + mp.getName());
            System.out.println("CollectionUsage:" + mp.getCollectionUsage());
            System.out.println("type:" + mp.getType());
        }
    }

    /**
     * 访问 MXBean 的方法的三种方法
     */
    public static void visitMBean(){

        // 第一种直接调用同一 Java 虚拟机内的 MXBean 中的方法。
        RuntimeMXBean mxbean = ManagementFactory.getRuntimeMXBean();
        String vendor1 = mxbean.getVmVendor();
        System.out.println("vendor1:" + vendor1);

        /* 第二种通过一个连接到正在运行的虚拟机的平台 MBeanServer 的 MBeanServerConnection。
        MBeanServerConnection mbs = null;
        // Connect to a running JVM (or itself) and get MBeanServerConnection
        // that has the JVM MXBeans registered in it

        try {
            // Assuming the RuntimeMXBean has been registered in mbs
            ObjectName oname = new ObjectName(ManagementFactory.RUNTIME_MXBEAN_NAME);
            String vendor2 = (String) mbs.getAttribute(oname, "VmVendor");
            System.out.println("vendor2:" + vendor2);
        } catch (Exception e) {
            e.printStackTrace();
        }
        */

        /* 第三种使用 MXBean 代理
        MBeanServerConnection mbs3 = null;
        RuntimeMXBean proxy;
        try {
            proxy = ManagementFactory.newPlatformMXBeanProxy(mbs3,ManagementFactory.RUNTIME_MXBEAN_NAME,
                                                     RuntimeMXBean.class);
            String vendor = proxy.getVmVendor();
        } catch (IOException e) {
            e.printStackTrace();
        }
        */
    }
}

4. 获取内存大小

下面的类实现了 jvm 内存各项指标的获取：

import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryPoolMXBean;
import java.lang.management.MemoryUsage;
import java.lang.management.OperatingSystemMXBean;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import java.util.Iterator;
import java.util.Locale;
import javax.management.MBeanServer;

public class MemoryInformations {
    private static final String NEXT = ",\n";
    private static final String MO = " Mo";
    private final long usedMemory = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory();
    private final long maxMemory = Runtime.getRuntime().maxMemory();
    private final long usedOldGen;
    private final long maxOldGen;
    private final long usedPermGen;
    private final long maxPermGen;
    private final long usedEdenSpace;
    private final long maxEdenSpace;
    private final long usedSurvivorSpace;
    private final long maxSurvivorSpace;
    private final long usedNonHeapMemory;
    private final long maxNonHeapMemory;
    private final int loadedClassesCount;
    private final long garbageCollectionTimeMillis;
    private final long usedPhysicalMemorySize;
    private final long usedSwapSpaceSize;
    private final String memoryDetails;
    private static MBeanServer mbeanServer = ManagementFactory.getPlatformMBeanServer();
    MemoryInformations() {
        MemoryPoolMXBean permGenMemoryPool = getPermGenMemoryPool();
        if(permGenMemoryPool != null) {
            MemoryUsage oldGenMemoryPool = permGenMemoryPool.getUsage();
            this.usedPermGen = oldGenMemoryPool.getUsed();
            this.maxPermGen = oldGenMemoryPool.getMax();
        } else {
            this.usedPermGen = 0L;
            this.maxPermGen = 0L;
        }
        MemoryPoolMXBean oldGenMemoryPool1 = getOldGenMemoryPool();
        if(oldGenMemoryPool1 != null) {
            MemoryUsage edenSpaceMemoryPool = oldGenMemoryPool1.getUsage();
            this.usedOldGen = edenSpaceMemoryPool.getUsed();
            this.maxOldGen = edenSpaceMemoryPool.getMax();
        } else {
            this.usedOldGen = 0L;
            this.maxOldGen = 0L;
        }
        MemoryPoolMXBean edenSpaceMemoryPool1 = getEdenSpacePool();
        if(edenSpaceMemoryPool1 != null) {
            MemoryUsage survivorSpacePool = edenSpaceMemoryPool1.getUsage();
            this.usedEdenSpace = survivorSpacePool.getUsed();
            this.maxEdenSpace = survivorSpacePool.getMax();
        } else {
            this.usedEdenSpace = 0L;
            this.maxEdenSpace = 0L;
        }
        MemoryPoolMXBean survivorSpacePool1 = getSurvivorSpaceMemoryPool();
        if(survivorSpacePool1 != null) {
            MemoryUsage operatingSystem = survivorSpacePool1.getUsage();
            this.usedSurvivorSpace = operatingSystem.getUsed();
            this.maxSurvivorSpace = operatingSystem.getMax();
        } else {
            this.usedSurvivorSpace = 0L;
            this.maxSurvivorSpace = 0L;
        }
        this.usedNonHeapMemory = ManagementFactory.getMemoryMXBean().getNonHeapMemoryUsage().getUsed();
        this.maxNonHeapMemory = ManagementFactory.getMemoryMXBean().getNonHeapMemoryUsage().getMax();
        this.loadedClassesCount = ManagementFactory.getClassLoadingMXBean().getLoadedClassCount();
        this.garbageCollectionTimeMillis = buildGarbageCollectionTimeMillis();
        OperatingSystemMXBean operatingSystem1 = ManagementFactory.getOperatingSystemMXBean();
        if(isSunOsMBean(operatingSystem1)) {
            com.sun.management.OperatingSystemMXBean osBean = (com.sun.management.OperatingSystemMXBean)operatingSystem1;
            this.usedPhysicalMemorySize = osBean.getTotalPhysicalMemorySize() - osBean.getFreePhysicalMemorySize();
            this.usedSwapSpaceSize = osBean.getTotalSwapSpaceSize() - osBean.getFreeSwapSpaceSize();
        } else {
            this.usedPhysicalMemorySize = 0L;
            this.usedSwapSpaceSize = 0L;
        }
        this.memoryDetails = this.buildMemoryDetails();
    }
    private static MemoryPoolMXBean getPermGenMemoryPool() {
        Iterator var0 = ManagementFactory.getMemoryPoolMXBeans().iterator();
        MemoryPoolMXBean memoryPool;
        do {
            if(!var0.hasNext()) {
                return null;
            }
            memoryPool = (MemoryPoolMXBean)var0.next();
        } while(!memoryPool.getName().endsWith("Perm Gen"));
        return memoryPool;
    }
    private static MemoryPoolMXBean getOldGenMemoryPool() {
        Iterator var0 = ManagementFactory.getMemoryPoolMXBeans().iterator();
        MemoryPoolMXBean memoryPool;
        do {
            if(!var0.hasNext()) {
                return null;
            }
            memoryPool = (MemoryPoolMXBean)var0.next();
        } while(!memoryPool.getName().endsWith("Old Gen"));
        return memoryPool;
    }
    private static MemoryPoolMXBean getEdenSpacePool() {
        Iterator var0 = ManagementFactory.getMemoryPoolMXBeans().iterator();
        MemoryPoolMXBean memoryPool;
        do {
            if(!var0.hasNext()) {
                return null;
            }
            memoryPool = (MemoryPoolMXBean)var0.next();
        } while(!memoryPool.getName().endsWith("Eden Space"));
        return memoryPool;
    }
    private static MemoryPoolMXBean getSurvivorSpaceMemoryPool() {
        Iterator var0 = ManagementFactory.getMemoryPoolMXBeans().iterator();
        MemoryPoolMXBean memoryPool;
        do {
            if(!var0.hasNext()) {
                return null;
            }
            memoryPool = (MemoryPoolMXBean)var0.next();
        } while(!memoryPool.getName().endsWith("Survivor Space"));
        return memoryPool;
    }
    private static long buildGarbageCollectionTimeMillis() {
        long garbageCollectionTime = 0L;
        GarbageCollectorMXBean garbageCollector;
        for(Iterator var2 = ManagementFactory.getGarbageCollectorMXBeans().iterator(); var2.hasNext(); garbageCollectionTime += garbageCollector.getCollectionTime()) {
            garbageCollector = (GarbageCollectorMXBean)var2.next();
        }
        return garbageCollectionTime;
    }
    private String buildMemoryDetails() {
        DecimalFormat integerFormat = new DecimalFormat("