jcmd命令实战
继续来根据之前的那篇infoq的文章的介绍熟悉工具，上一次咱们学习使用了：
接下来学习它里面提到的另一个工具：
jcmd是一个非常之强大的命令行工具，能输出很多很多的信息，也是在处理JVM的一些问题经常要接触到的一个工具，这个命令也是需要一个进程ID的，而在之前咱们来查询pid时是使用了一个不是特别简明的一个方式，回忆一下：
其实jdk提供了一个jps来获取JVM进程的所有pid信息，而且非常简洁，下面来瞅一下：
可以查看一下它的使用帮助：
加上不同的参数其输出也会不一样，简单的演练一下：
其实最常用的是：
还可以：
总之，之后查看JVM可以用jps来代替之前的ps繁琐方式啦，接下来用一下jcmd命令，直接敲它：
貌似跟jps命令没啥大的区别，都是获取当前JVM进程的一些信息，也就是简单的jcmd命令跟jps在打印JVM信息上是可以互换的，当然要是jcmd只有这个功能那也不会专门来学习它了，先来瞅一下它的帮助使用说明：
jcmd pid VM.flags：查看JVM的启动参数
接下来具体用jcmd来查询JVM的一些东东，先来查看一下JVM的启动参数，首先还是运行一下MyTest5这个程序：
然后查看一下它进程：
接下来用jcmd来查看一下此进程的JVM启动参数，可以：
这就可以清晰的通过命令的方式来查看到启动参数啦，还是很方便。
由于MyTest5这个程序木有手动配置自己的JVM启动参数：
这里换成MyTest4，因为它配启动参数了：
启动一下它，然后再查看一下：
jcmd pid help：列出当前运行的Java进程可以执行的操作。
在上面查看JVM的启动参数命令中，有个东东很奇怪：
那这些操作来源于哪里呢？其实可以通过标题所示的这个命令来查看，咱们还是以MyTest5运行为例演示一下它的用法：
也可以明显感受到jcmd的强大之处，上面这么多只挑重点来学习。
jcmd pid help JFR.dump：查看具体命令的选项。
我们已经知道了命令可以跟一些哪些执行操作，那具体操作的选项又有哪些呢，于是乎用它就可以了，以JFR.dump为例：
jcmd pid PerfCounter.print：查看JVM性能相关的参数。
直接试验一下：
xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 97595 help JFR.dump 97595: JFR.dump Copies contents of a JFR recording to file. Either the name or the recording id must be specified. Impact: Low Permission: java.lang.management.ManagementPermission(monitor) Syntax : JFR.dump [options] Options: (options must be specified using the <key> or <key>=<value> syntax) name : [optional] Recording name, e.g. \"My Recording\" (STRING, no default value) recording : [optional] Recording number, use JFR.check to list available recordings (JLONG, -1) filename : Copy recording data to file, i.e \"/Users/user/My Recording.jfr\" (STRING, no default value) compress : [optional] GZip-compress "filename" destination (BOOLEAN, false) xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 97595 PerfCounter.print 97595: java.ci.totalTime=94549036 java.cls.loadedClasses=516 java.cls.sharedLoadedClasses=0 java.cls.sharedUnloadedClasses=0 java.cls.unloadedClasses=0 java.property.java.class.path="/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Conten" java.property.java.endorsed.dirs="/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/endorsed" java.property.java.ext.dirs="/Users/xiongwei/Library/Java/Extensions:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java" java.property.java.home="/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre" java.property.java.library.path="/Users/xiongwei/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:." java.property.java.version="1.8.0_92" java.property.java.vm.info="mixed mode" java.property.java.vm.name="Java HotSpot(TM) 64-Bit Server VM" java.property.java.vm.specification.name="Java Virtual Machine Specification" java.property.java.vm.specification.vendor="Oracle Corporation" java.property.java.vm.specification.version="1.8" java.property.java.vm.vendor="Oracle Corporation" java.property.java.vm.version="25.92-b14" java.rt.vmArgs="-Dfile.encoding=UTF-8" java.rt.vmFlags="" java.threads.daemon=4 java.threads.live=5 java.threads.livePeak=5 java.threads.started=5 sun.ci.compilerThread.0.compiles=3 sun.ci.compilerThread.0.method="" sun.ci.compilerThread.0.time=2053 sun.ci.compilerThread.0.type=1 sun.ci.compilerThread.1.compiles=1 sun.ci.compilerThread.1.method="" sun.ci.compilerThread.1.time=313 sun.ci.compilerThread.1.type=1 sun.ci.compilerThread.2.compiles=118 sun.ci.compilerThread.2.method="" sun.ci.compilerThread.2.time=41561 sun.ci.compilerThread.2.type=1 sun.ci.lastFailedMethod="" sun.ci.lastFailedType=0 sun.ci.lastInvalidatedMethod="" sun.ci.lastInvalidatedType=0 sun.ci.lastMethod="java/lang/String indexOf" sun.ci.lastSize=70 sun.ci.lastType=1 sun.ci.nmethodCodeSize=124064 sun.ci.nmethodSize=206088 sun.ci.osrBytes=0 sun.ci.osrCompiles=0 sun.ci.osrTime=0 sun.ci.standardBytes=8561 sun.ci.standardCompiles=122 sun.ci.standardTime=94549036 sun.ci.threads=3 sun.ci.totalBailouts=0 sun.ci.totalCompiles=122 sun.ci.totalInvalidates=0 sun.classloader.findClassTime=75394974 sun.classloader.findClasses=1 sun.classloader.parentDelegationTime=75632149 sun.cls.appClassBytes=795 sun.cls.appClassLoadCount=7 sun.cls.appClassLoadTime=1380939 sun.cls.appClassLoadTime.self=1379136 sun.cls.classInitTime=200207388 sun.cls.classInitTime.self=83134592 sun.cls.classLinkedTime=30790764 sun.cls.classLinkedTime.self=27199048 sun.cls.classVerifyTime=3495135 sun.cls.classVerifyTime.self=2190525 sun.cls.defineAppClassTime=185979 sun.cls.defineAppClassTime.self=12729 sun.cls.defineAppClasses=1 sun.cls.initializedClasses=417 sun.cls.isUnsyncloadClassSet=0 sun.cls.jniDefineClassNoLockCalls=0 sun.cls.jvmDefineClassNoLockCalls=1 sun.cls.jvmFindLoadedClassNoLockCalls=20 sun.cls.linkedClasses=459 sun.cls.loadInstanceClassFailRate=0 sun.cls.loadedBytes=1076800 sun.cls.lookupSysClassTime=179168672 sun.cls.methodBytes=685560 sun.cls.nonSystemLoaderLockContentionRate=0 sun.cls.parseClassTime=108368386 sun.cls.parseClassTime.self=70142981 sun.cls.sharedClassLoadTime=70544 sun.cls.sharedLoadedBytes=0 sun.cls.sharedUnloadedBytes=0 sun.cls.sysClassBytes=1950237 sun.cls.sysClassLoadTime=324675751 sun.cls.systemLoaderLockContentionRate=0 sun.cls.time=363112365 sun.cls.unloadedBytes=0 sun.cls.unsafeDefineClassCalls=0 sun.cls.verifiedClasses=459 sun.gc.cause="No GC" sun.gc.collector.0.invocations=0 sun.gc.collector.0.lastEntryTime=0 sun.gc.collector.0.lastExitTime=0 sun.gc.collector.0.name="PSScavenge" sun.gc.collector.0.time=0 sun.gc.collector.1.invocations=0 sun.gc.collector.1.lastEntryTime=0 sun.gc.collector.1.lastExitTime=0 sun.gc.collector.1.name="PSParallelCompact" sun.gc.collector.1.time=0 sun.gc.compressedclassspace.capacity=393216 sun.gc.compressedclassspace.maxCapacity=1073741824 sun.gc.compressedclassspace.minCapacity=0 sun.gc.compressedclassspace.used=77664 sun.gc.generation.0.capacity=44564480 sun.gc.generation.0.maxCapacity=715653120 sun.gc.generation.0.minCapacity=44564480 sun.gc.generation.0.name="new" sun.gc.generation.0.space.0.capacity=34078720 sun.gc.generation.0.space.0.initCapacity=0 sun.gc.generation.0.space.0.maxCapacity=714604544 sun.gc.generation.0.space.0.name="eden" sun.gc.generation.0.space.0.used=3408368 sun.gc.generation.0.space.1.capacity=5242880 sun.gc.generation.0.space.1.initCapacity=0 sun.gc.generation.0.space.1.maxCapacity=238551040 sun.gc.generation.0.space.1.name="s0" sun.gc.generation.0.space.1.used=0 sun.gc.generation.0.space.2.capacity=5242880 sun.gc.generation.0.space.2.initCapacity=0 sun.gc.generation.0.space.2.maxCapacity=238551040 sun.gc.generation.0.space.2.name="s1" sun.gc.generation.0.space.2.used=0 sun.gc.generation.0.spaces=3 sun.gc.generation.1.capacity=89653248 sun.gc.generation.1.maxCapacity=1431830528 sun.gc.generation.1.minCapacity=89653248 sun.gc.generation.1.name="old" sun.gc.generation.1.space.0.capacity=89653248 sun.gc.generation.1.space.0.initCapacity=89653248 sun.gc.generation.1.space.0.maxCapacity=1431830528 sun.gc.generation.1.space.0.name="old" sun.gc.generation.1.space.0.used=0 sun.gc.generation.1.spaces=1 sun.gc.lastCause="No GC" sun.gc.metaspace.capacity=4587520 sun.gc.metaspace.maxCapacity=1082130432 sun.gc.metaspace.minCapacity=0 sun.gc.metaspace.used=792432 sun.gc.policy.avgBaseFootprint=0 sun.gc.policy.avgMajorIntervalTime=0 sun.gc.policy.avgMajorPauseTime=0 sun.gc.policy.avgMinorIntervalTime=0 sun.gc.policy.avgMinorPauseTime=0 sun.gc.policy.avgOldLive=0 sun.gc.policy.avgPretenuredPaddedAvg=0 sun.gc.policy.avgPromotedAvg=34078720 sun.gc.policy.avgPromotedDev=0 sun.gc.policy.avgPromotedPaddedAvg=34078720 sun.gc.policy.avgSurvivedAvg=5242880 sun.gc.policy.avgSurvivedDev=0 sun.gc.policy.avgSurvivedPaddedAvg=5242880 sun.gc.policy.avgYoungLive=0 sun.gc.policy.boundaryMoved=0 sun.gc.policy.changeOldGenForMajPauses=0 sun.gc.policy.changeOldGenForMinPauses=0 sun.gc.policy.changeYoungGenForMajPauses=0 sun.gc.policy.changeYoungGenForMinPauses=0 sun.gc.policy.collectors=2 sun.gc.policy.decideAtFullGc=0 sun.gc.policy.decreaseForFootprint=0 sun.gc.policy.decrementTenuringThresholdForGcCost=0 sun.gc.policy.decrementTenuringThresholdForSurvivorLimit=0 sun.gc.policy.desiredSurvivorSize=0 sun.gc.policy.edenSize=34078720 sun.gc.policy.freeSpace=68157440 sun.gc.policy.fullFollowsScavenge=0 sun.gc.policy.gcTimeLimitExceeded=0 sun.gc.policy.generations=3 sun.gc.policy.increaseOldGenForThroughput=0 sun.gc.policy.increaseYoungGenForThroughput=0 sun.gc.policy.incrementTenuringThresholdForGcCost=0 sun.gc.policy.liveAtLastFullGc=34078720 sun.gc.policy.liveSpace=0 sun.gc.policy.majorCollectionSlope=0 sun.gc.policy.majorGcCost=0 sun.gc.policy.majorPauseOldSlope=0 sun.gc.policy.majorPauseYoungSlope=0 sun.gc.policy.maxTenuringThreshold=15 sun.gc.policy.minorCollectionSlope=0 sun.gc.policy.minorGcCost=0 sun.gc.policy.minorPauseOldSlope=0 sun.gc.policy.minorPauseTime=0 sun.gc.policy.minorPauseYoungSlope=0 sun.gc.policy.mutatorCost=1 sun.gc.policy.name="ParScav:MSC" sun.gc.policy.oldCapacity=134217728 sun.gc.policy.oldEdenSize=34078720 sun.gc.policy.oldPromoSize=34078720 sun.gc.policy.promoSize=34078720 sun.gc.policy.promoted=0 sun.gc.policy.scavengeSkipped=0 sun.gc.policy.survived=0 sun.gc.policy.survivorOverflowed=0 sun.gc.policy.tenuringThreshold=15 sun.gc.policy.youngCapacity=39321600 sun.gc.tlab.alloc=0 sun.gc.tlab.allocThreads=0 sun.gc.tlab.fastWaste=0 sun.gc.tlab.fills=0 sun.gc.tlab.gcWaste=0 sun.gc.tlab.maxFastWaste=0 sun.gc.tlab.maxFills=0 sun.gc.tlab.maxGcWaste=0 sun.gc.tlab.maxSlowAlloc=0 sun.gc.tlab.maxSlowWaste=0 sun.gc.tlab.slowAlloc=0 sun.gc.tlab.slowWaste=0 sun.os.hrt.frequency=1000000000 sun.os.hrt.ticks=714050340882 sun.perfdata.majorVersion=2 sun.perfdata.minorVersion=0 sun.perfdata.overflow=0 sun.perfdata.size=32768 sun.perfdata.timestamp=553597942 sun.perfdata.used=18848 sun.property.sun.boot.class.path="/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/sunrsasign.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/classes" sun.property.sun.boot.library.path="/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib" sun.rt._sync_ContendedLockAttempts=0 sun.rt._sync_Deflations=3 sun.rt._sync_EmptyNotifications=0 sun.rt._sync_FailedSpins=0 sun.rt._sync_FutileWakeups=0 sun.rt._sync_Inflations=5 sun.rt._sync_MonExtant=128 sun.rt._sync_MonInCirculation=0 sun.rt._sync_MonScavenged=0 sun.rt._sync_Notifications=2 sun.rt._sync_Parks=2 sun.rt._sync_PrivateA=0 sun.rt._sync_PrivateB=0 sun.rt._sync_SlowEnter=0 sun.rt._sync_SlowExit=0 sun.rt._sync_SlowNotify=0 sun.rt._sync_SlowNotifyAll=0 sun.rt._sync_SuccessfulSpins=0 sun.rt.applicationTime=429558101791 sun.rt.createVmBeginTime=1555054870552 sun.rt.createVmEndTime=1555054871042 sun.rt.internalVersion="Java HotSpot(TM) 64-Bit Server VM (25.92-b14) for bsd-amd64 JRE (1.8.0_92-b14), built on Mar 31 2016 21:23:14 by "java_re" with gcc 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 2336.11.00)" sun.rt.interruptedBeforeIO=0 sun.rt.interruptedDuringIO=0 sun.rt.javaCommand="com.jvm.memory.MyTest5" sun.rt.jvmCapabilities="1100000000000000000000000000000000000000000000000000000000000000" sun.rt.jvmVersion=425459726 sun.rt.safepointSyncTime=676359 sun.rt.safepointTime=1471726 sun.rt.safepoints=7 sun.rt.threadInterruptSignaled=0 sun.rt.vmInitDoneTime=1555054870846 sun.threads.vmOperationTime=57519 sun.urlClassLoader.readClassBytesTime=1087499 sun.zip.zipFile.openTime=77754125 sun.zip.zipFiles=19 xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$
真的太多了。。
jcmd pid VM.uptime：查看JVM的启动时长。
jcmd pid GC.class_histogram：查看系统中类的统计信息。
xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 97595 GC.class_histogram 97595: num #instances #bytes class name ---------------------------------------------- 1: 3329 238320 [C 2: 441 128256 [B 3: 3308 79392 java.lang.String 4: 591 67184 java.lang.Class 5: 586 35408 [Ljava.lang.Object; 6: 631 25240 java.util.LinkedHashMap$Entry 7: 287 13088 [Ljava.lang.String; 8: 360 11520 java.util.HashMap$Node 9: 22 8480 [Ljava.util.HashMap$Node; 10: 118 7040 [I 11: 98 6272 java.net.URL 12: 79 5688 java.lang.reflect.Field 13: 256 4096 java.lang.Integer 14: 99 3960 java.lang.ref.SoftReference 15: 116 3712 java.util.Hashtable$Entry 16: 67 2680 java.lang.ref.Finalizer 17: 7 2632 java.lang.Thread 18: 74 2368 java.util.concurrent.ConcurrentHashMap$Node 19: 45 2160 sun.misc.URLClassPath$JarLoader 20: 39 1872 sun.util.locale.LocaleObjectCache$CacheEntry 21: 22 1760 [Ljava.util.WeakHashMap$Entry; 22: 16 1664 [Ljava.util.concurrent.ConcurrentHashMap$Node; 23: 1 1520 [[B 24: 18 1440 java.lang.reflect.Constructor 25: 28 1344 java.util.HashMap 26: 23 1288 sun.nio.cs.UTF_8$Encoder 27: 20 1280 java.util.concurrent.ConcurrentHashMap 28: 13 1248 java.util.jar.JarFile$JarFileEntry 29: 19 1216 java.util.jar.JarFile 30: 8 1120 [Ljava.util.Hashtable$Entry; 31: 2 1064 [Ljava.lang.invoke.MethodHandle; 32: 44 1056 java.io.ExpiringCache$Entry 33: 22 1056 java.util.WeakHashMap 34: 1 1040 [Ljava.lang.Integer; 35: 26 1040 java.io.ObjectStreamField 36: 18 1008 java.lang.Class$ReflectionData 37: 29 928 java.lang.ref.ReferenceQueue 38: 15 840 java.util.zip.ZipFile$ZipFileInputStream 39: 48 768 java.lang.Object 40: 19 760 sun.util.locale.BaseLocale$Key 41: 12 672 java.util.zip.ZipFile$ZipFileInflaterInputStream 42: 8 640 [S 43: 19 608 java.util.Locale 44: 19 608 java.util.zip.ZipCoder 45: 19 608 sun.util.locale.BaseLocale 46: 12 576 java.util.zip.Inflater 47: 17 544 java.io.File 48: 31 496 java.lang.ref.ReferenceQueue$Lock 49: 8 456 [Ljava.lang.reflect.Field; 50: 19 456 java.util.ArrayDeque 51: 19 456 java.util.Locale$LocaleKey 52: 11 440 java.security.AccessControlContext 53: 1 384 java.lang.ref.Finalizer$FinalizerThread 54: 6 384 java.nio.DirectByteBuffer 55: 16 384 sun.misc.MetaIndex 56: 1 376 java.lang.ref.Reference$ReferenceHandler 57: 15 360 java.util.LinkedList$Node 58: 6 336 java.nio.DirectLongBufferU 59: 10 320 java.lang.OutOfMemoryError 60: 10 288 [Ljava.io.ObjectStreamField; 61: 9 288 java.util.LinkedList 62: 12 288 java.util.zip.ZStreamRef 63: 7 280 java.util.WeakHashMap$Entry 64: 5 280 sun.util.calendar.ZoneInfo 65: 8 256 java.io.FileDescriptor 66: 8 256 java.util.Vector 67: 12 240 [Ljava.lang.Class; 68: 5 240 java.util.Hashtable 69: 2 216 [J 70: 9 216 [Ljava.lang.reflect.Constructor; 71: 9 216 java.util.ArrayList 72: 9 216 sun.reflect.NativeConstructorAccessorImpl 73: 2 160 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry; 74: 5 160 java.io.FileInputStream 75: 4 160 java.security.ProtectionDomain 76: 5 160 sun.util.locale.provider.LocaleProviderAdapter$Type 77: 3 144 java.util.Properties 78: 6 144 sun.misc.PerfCounter 79: 3 144 sun.misc.URLClassPath 80: 9 144 sun.reflect.DelegatingConstructorAccessorImpl 81: 2 128 java.io.ExpiringCache$1 82: 4 128 java.lang.ThreadLocal$ThreadLocalMap$Entry 83: 4 128 java.security.CodeSource 84: 4 128 java.util.Stack 85: 1 120 [[Ljava.lang.String; 86: 5 120 java.util.Collections$UnmodifiableRandomAccessList 87: 2 112 java.util.LinkedHashMap 88: 2 112 java.util.ResourceBundle$CacheKey 89: 3 96 java.io.FileOutputStream 90: 2 96 java.lang.ThreadGroup 91: 2 96 java.nio.HeapByteBuffer 92: 2 96 java.util.ResourceBundle$BundleReference 93: 1 96 sun.misc.Launcher$AppClassLoader 94: 2 96 sun.nio.cs.StreamEncoder 95: 1 88 java.lang.reflect.Method 96: 1 88 sun.misc.Launcher$ExtClassLoader 97: 2 80 java.io.BufferedWriter 98: 2 80 java.io.ExpiringCache 99: 2 80 sun.nio.cs.UTF_8$Decoder 100: 3 72 java.lang.RuntimePermission 101: 3 72 java.util.Arrays$ArrayList 102: 3 72 java.util.Collections$SynchronizedSet 103: 1 72 java.util.ResourceBundle$RBClassLoader 104: 3 72 java.util.concurrent.atomic.AtomicLong 105: 3 72 sun.misc.Signal 106: 1 72 sun.util.locale.provider.JRELocaleProviderAdapter 107: 2 64 [Ljava.lang.Thread; 108: 4 64 [Ljava.security.Principal; 109: 2 64 java.io.PrintStream 110: 2 64 java.lang.ClassValue$Entry 111: 2 64 java.lang.StringCoding$StringDecoder 112: 2 64 java.lang.StringCoding$StringEncoder 113: 2 64 java.lang.VirtualMachineError 114: 2 64 java.lang.ref.ReferenceQueue$Null 115: 4 64 java.security.ProtectionDomain$Key 116: 4 64 java.util.HashSet 117: 2 64 java.util.ResourceBundle$LoaderReference 118: 1 56 java.lang.Package 119: 2 48 java.io.BufferedOutputStream 120: 2 48 java.io.File$PathStatus 121: 2 48 java.io.OutputStreamWriter 122: 3 48 java.lang.ThreadLocal 123: 2 48 java.lang.ThreadLocal$ThreadLocalMap 124: 2 48 java.nio.charset.CoderResult 125: 3 48 java.nio.charset.CodingErrorAction 126: 2 48 sun.misc.JarIndex 127: 2 48 sun.misc.NativeSignalHandler 128: 3 48 sun.net.www.protocol.jar.Handler 129: 1 48 sun.util.locale.provider.LocaleResources$ResourceReference 130: 1 48 sun.util.resources.TimeZoneNames 131: 1 48 sun.util.resources.en.TimeZoneNames_en 132: 1 40 [Lsun.util.locale.provider.LocaleProviderAdapter$Type; 133: 1 40 java.io.BufferedInputStream 134: 1 40 java.lang.ClassLoader$NativeLibrary 135: 1 40 java.util.ResourceBundle$1 136: 1 40 sun.nio.cs.StandardCharsets$Aliases 137: 1 40 sun.nio.cs.StandardCharsets$Cache 138: 1 40 sun.nio.cs.StandardCharsets$Classes 139: 1 32 [Ljava.lang.OutOfMemoryError; 140: 2 32 [Ljava.lang.StackTraceElement; 141: 1 32 [Ljava.lang.ThreadGroup; 142: 1 32 java.io.FilePermission 143: 1 32 java.io.UnixFileSystem 144: 1 32 java.lang.ArithmeticException 145: 2 32 java.lang.Boolean 146: 1 32 java.lang.NullPointerException 147: 2 32 java.nio.ByteOrder 148: 1 32 java.security.BasicPermissionCollection 149: 1 32 java.security.Permissions 150: 2 32 java.util.LinkedHashMap$LinkedKeySet 151: 2 32 java.util.concurrent.atomic.AtomicInteger 152: 1 32 java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl 153: 1 32 sun.nio.cs.StandardCharsets 154: 1 32 sun.util.locale.provider.LocaleResources 155: 1 32 sun.util.locale.provider.LocaleServiceProviderPool 156: 1 24 [Ljava.io.File$PathStatus; 157: 1 24 [Ljava.lang.ClassValue$Entry; 158: 1 24 [Ljava.lang.reflect.Method; 159: 1 24 [Lsun.launcher.LauncherHelper; 160: 1 24 java.io.FilePermissionCollection 161: 1 24 java.lang.ClassValue$Version 162: 1 24 java.lang.StringBuilder 163: 1 24 java.lang.invoke.MethodHandleImpl$4 164: 1 24 java.lang.reflect.ReflectPermission 165: 1 24 java.util.BitSet 166: 1 24 java.util.Collections$EmptyMap 167: 1 24 java.util.Collections$SetFromMap 168: 1 24 java.util.Locale$Cache 169: 1 24 java.util.ResourceBundle$Control$CandidateListCache 170: 1 24 sun.launcher.LauncherHelper 171: 1 24 sun.misc.URLClassPath$FileLoader 172: 1 24 sun.nio.cs.ISO_8859_1 173: 1 24 sun.nio.cs.US_ASCII 174: 1 24 sun.nio.cs.UTF_16 175: 1 24 sun.nio.cs.UTF_16BE 176: 1 24 sun.nio.cs.UTF_16LE 177: 1 24 sun.nio.cs.UTF_8 178: 1 24 sun.util.locale.BaseLocale$Cache 179: 1 24 sun.util.locale.provider.TimeZoneNameProviderImpl 180: 1 16 [Ljava.lang.Throwable; 181: 1 16 [Ljava.security.cert.Certificate; 182: 1 16 java.io.FileDescriptor$1 183: 1 16 java.lang.CharacterDataLatin1 184: 1 16 java.lang.ClassValue$Identity 185: 1 16 java.lang.Runtime 186: 1 16 java.lang.String$CaseInsensitiveComparator 187: 1 16 java.lang.System$2 188: 1 16 java.lang.Terminator$1 189: 1 16 java.lang.invoke.MemberName$Factory 190: 1 16 java.lang.invoke.MethodHandleImpl$2 191: 1 16 java.lang.invoke.MethodHandleImpl$3 192: 1 16 java.lang.ref.Reference$1 193: 1 16 java.lang.ref.Reference$Lock 194: 1 16 java.lang.reflect.ReflectAccess 195: 1 16 java.net.URLClassLoader$7 196: 1 16 java.nio.Bits$1 197: 1 16 java.nio.charset.CoderResult$1 198: 1 16 java.nio.charset.CoderResult$2 199: 1 16 java.security.ProtectionDomain$2 200: 1 16 java.security.ProtectionDomain$JavaSecurityAccessImpl 201: 1 16 java.util.Collections$EmptyIterator 202: 1 16 java.util.Collections$EmptyList 203: 1 16 java.util.Collections$EmptySet 204: 1 16 java.util.Hashtable$EntrySet 205: 1 16 java.util.ResourceBundle$Control 206: 1 16 java.util.WeakHashMap$KeySet 207: 1 16 java.util.concurrent.atomic.AtomicBoolean 208: 1 16 java.util.jar.JavaUtilJarAccessImpl 209: 1 16 java.util.zip.ZipFile$1 210: 1 16 sun.misc.Launcher 211: 1 16 sun.misc.Launcher$Factory 212: 1 16 sun.misc.Perf 213: 1 16 sun.misc.Unsafe 214: 1 16 sun.net.www.protocol.file.Handler 215: 1 16 sun.reflect.ReflectionFactory 216: 1 16 sun.util.calendar.Gregorian 217: 1 16 sun.util.locale.provider.AuxLocaleProviderAdapter$NullProvider 218: 1 16 sun.util.locale.provider.SPILocaleProviderAdapter 219: 1 16 sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter 220: 1 16 sun.util.resources.LocaleData 221: 1 16 sun.util.resources.LocaleData$LocaleDataResourceBundleControl Total 11547 692336 xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$
jcmd pid Thread.print：查看线程堆栈信息。
xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 97595 Thread.print 97595: 2019-04-12 15:58:30 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.92-b14 mixed mode): "Attach Listener" #9 daemon prio=9 os_prio=31 tid=0x00007fb6d3906800 nid=0x3803 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Service Thread" #8 daemon prio=9 os_prio=31 tid=0x00007fb6d300c000 nid=0x3603 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C1 CompilerThread2" #7 daemon prio=9 os_prio=31 tid=0x00007fb6d281e800 nid=0x4503 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread1" #6 daemon prio=9 os_prio=31 tid=0x00007fb6d2809800 nid=0x3503 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" #5 daemon prio=9 os_prio=31 tid=0x00007fb6d280c800 nid=0x3403 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fb6d300b000 nid=0x3303 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fb6d201f000 nid=0x4f03 in Object.wait() [0x0000700008a96000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x0000000740010020> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x0000000740010020> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209) "Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fb6d301f000 nid=0x2b03 in Object.wait() [0x0000700008993000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x0000000740010010> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:502) at java.lang.ref.Reference.tryHandlePending(Reference.java:191) - locked <0x0000000740010010> (a java.lang.ref.Reference$Lock) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153) "main" #1 prio=5 os_prio=31 tid=0x00007fb6d3805800 nid=0x2803 waiting on condition [0x0000700008381000] java.lang.Thread.State: TIMED_WAITING (sleeping) at java.lang.Thread.sleep(Native Method) at com.jvm.memory.MyTest5.main(MyTest5.java:8) "VM Thread" os_prio=31 tid=0x00007fb6d2805000 nid=0x5103 runnable "GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fb6d3811800 nid=0x1e07 runnable "GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fb6d3812000 nid=0x2103 runnable "GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fb6d2000800 nid=0x2a03 runnable "GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fb6d3812800 nid=0x5303 runnable "VM Periodic Task Thread" os_prio=31 tid=0x00007fb6d200a800 nid=0x3703 waiting on condition JNI global references: 6
貌似上面这个在jconsole和jvisualvm可视化的工具中都能看到，也就是GUI工具看到的也是集成了jcmd的命令工具了，关于线程貌似之前我们写过一个死锁的例子，这里再运行一下这个程序来用这个命令观测一下：
xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jps -l 98017 com.jvm.memory.MyTest3 96336 org.gradle.launcher.daemon.bootstrap.GradleDaemon 94336 98016 org.jetbrains.jps.cmdline.Launcher 98024 sun.tools.jps.Jps 17418 96495 org.gradle.launcher.daemon.bootstrap.GradleDaemon xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 98017 Thread.print 98017: 2019-04-12 16:02:00 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.92-b14 mixed mode): "Attach Listener" #12 daemon prio=9 os_prio=31 tid=0x00007fc497931000 nid=0x4203 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "DestroyJavaVM" #11 prio=5 os_prio=31 tid=0x00007fc497829800 nid=0x2803 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Thread-B" #10 prio=5 os_prio=31 tid=0x00007fc4968fa000 nid=0x4103 waiting for monitor entry [0x00007000014e0000] java.lang.Thread.State: BLOCKED (on object monitor) at com.jvm.memory.A.method(MyTest3.java:17) - waiting to lock <0x00000007958c2f10> (a java.lang.Class for com.jvm.memory.A) at com.jvm.memory.B.method(MyTest3.java:35) - locked <0x0000000795a0fcb0> (a java.lang.Class for com.jvm.memory.B) at com.jvm.memory.MyTest3.lambda$main$1(MyTest3.java:10) at com.jvm.memory.MyTest3$$Lambda$2/1989780873.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Thread-A" #9 prio=5 os_prio=31 tid=0x00007fc4968f9800 nid=0x4703 waiting for monitor entry [0x00007000013dd000] java.lang.Thread.State: BLOCKED (on object monitor) at com.jvm.memory.B.method(MyTest3.java:31) - waiting to lock <0x0000000795a0fcb0> (a java.lang.Class for com.jvm.memory.B) at com.jvm.memory.A.method(MyTest3.java:21) - locked <0x00000007958c2f10> (a java.lang.Class for com.jvm.memory.A) at com.jvm.memory.MyTest3.lambda$main$0(MyTest3.java:6) at com.jvm.memory.MyTest3$$Lambda$1/2093631819.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Service Thread" #8 daemon prio=9 os_prio=31 tid=0x00007fc49680c800 nid=0x4903 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C1 CompilerThread2" #7 daemon prio=9 os_prio=31 tid=0x00007fc496804800 nid=0x3d03 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread1" #6 daemon prio=9 os_prio=31 tid=0x00007fc49703d800 nid=0x4b03 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "C2 CompilerThread0" #5 daemon prio=9 os_prio=31 tid=0x00007fc497017000 nid=0x3a03 waiting on condition [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Signal Dispatcher" #4 daemon prio=9 os_prio=31 tid=0x00007fc498031000 nid=0x3803 runnable [0x0000000000000000] java.lang.Thread.State: RUNNABLE "Finalizer" #3 daemon prio=8 os_prio=31 tid=0x00007fc496820000 nid=0x5003 in Object.wait() [0x0000700000c45000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x0000000795588ee0> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143) - locked <0x0000000795588ee0> (a java.lang.ref.ReferenceQueue$Lock) at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:164) at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209) "Reference Handler" #2 daemon prio=10 os_prio=31 tid=0x00007fc497808000 nid=0x5103 in Object.wait() [0x0000700000b42000] java.lang.Thread.State: WAITING (on object monitor) at java.lang.Object.wait(Native Method) - waiting on <0x0000000795586b50> (a java.lang.ref.Reference$Lock) at java.lang.Object.wait(Object.java:502) at java.lang.ref.Reference.tryHandlePending(Reference.java:191) - locked <0x0000000795586b50> (a java.lang.ref.Reference$Lock) at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153) "VM Thread" os_prio=31 tid=0x00007fc498028800 nid=0x2c03 runnable "GC task thread#0 (ParallelGC)" os_prio=31 tid=0x00007fc497009000 nid=0x2207 runnable "GC task thread#1 (ParallelGC)" os_prio=31 tid=0x00007fc497009800 nid=0x1f03 runnable "GC task thread#2 (ParallelGC)" os_prio=31 tid=0x00007fc49700a000 nid=0x2a03 runnable "GC task thread#3 (ParallelGC)" os_prio=31 tid=0x00007fc49700a800 nid=0x5403 runnable "VM Periodic Task Thread" os_prio=31 tid=0x00007fc497812000 nid=0x4803 waiting on condition JNI global references: 309 Found one Java-level deadlock: ============================= "Thread-B": waiting to lock monitor 0x00007fc4980308a8 (object 0x00000007958c2f10, a java.lang.Class), which is held by "Thread-A" "Thread-A": waiting to lock monitor 0x00007fc49802e018 (object 0x0000000795a0fcb0, a java.lang.Class), which is held by "Thread-B" Java stack information for the threads listed above: =================================================== "Thread-B": at com.jvm.memory.A.method(MyTest3.java:17) - waiting to lock <0x00000007958c2f10> (a java.lang.Class for com.jvm.memory.A) at com.jvm.memory.B.method(MyTest3.java:35) - locked <0x0000000795a0fcb0> (a java.lang.Class for com.jvm.memory.B) at com.jvm.memory.MyTest3.lambda$main$1(MyTest3.java:10) at com.jvm.memory.MyTest3$$Lambda$2/1989780873.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) "Thread-A": at com.jvm.memory.B.method(MyTest3.java:31) - waiting to lock <0x0000000795a0fcb0> (a java.lang.Class for com.jvm.memory.B) at com.jvm.memory.A.method(MyTest3.java:21) - locked <0x00000007958c2f10> (a java.lang.Class for com.jvm.memory.A) at com.jvm.memory.MyTest3.lambda$main$0(MyTest3.java:6) at com.jvm.memory.MyTest3$$Lambda$1/2093631819.run(Unknown Source) at java.lang.Thread.run(Thread.java:745) Found 1 deadlock.
如我们之前在jconsole或jvisualvm看到的一样，之所以要学习命令行工具是因为有时候可能不能使用GUI工具，这时命令行工具就可以发挥其作用了。
jcmd pid GC.heap_jump filename：导出Heap dump文件，导出的文件可以通过jvisualvm查看。
还是回到MyTest5这个例子：
此时在桌在上就可以看到这个转储文件了：
我们可以用jvisualvm看能否正常打开它：
木问题的~~
jcmd pid VM.system_properties：查看JVM的属性信息。
xiongweideMacBook-Pro:CoffeeMachineClient xiongwei$ jcmd 98073 VM.system_properties 98073: #Fri Apr 12 16:12:20 CST 2019 java.runtime.name=Java(TM) SE Runtime Environment sun.boot.library.path=/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib java.vm.version=25.92-b14 gopherProxySet=false java.vm.vendor=Oracle Corporation java.vendor.url=http\://java.oracle.com/ path.separator=\: java.vm.name=Java HotSpot(TM) 64-Bit Server VM file.encoding.pkg=sun.io user.country=CN sun.java.launcher=SUN_STANDARD sun.os.patch.level=unknown java.vm.specification.name=Java Virtual Machine Specification user.dir=/Users/xiongwei/Documents/workspace/IntelliJSpace/jvm_lectue java.runtime.version=1.8.0_92-b14 java.awt.graphicsenv=sun.awt.CGraphicsEnvironment java.endorsed.dirs=/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/endorsed os.arch=x86_64 java.io.tmpdir=/var/folders/80/ckcy6rp51vg303j_q084yc7w0000gn/T/ line.separator=\n java.vm.specification.vendor=Oracle Corporation os.name=Mac OS X sun.jnu.encoding=UTF-8 java.library.path=/Users/xiongwei/Library/Java/Extensions\:/Library/Java/Extensions\:/Network/Library/Java/Extensions\:/System/Library/Java/Extensions\:/usr/lib/java\:. java.specification.name=Java Platform API Specification java.class.version=52.0 sun.management.compiler=HotSpot 64-Bit Tiered Compilers os.version=10.13.6 user.home=/Users/xiongwei user.timezone=Asia/Shanghai java.awt.printerjob=sun.lwawt.macosx.CPrinterJob file.encoding=UTF-8 java.specification.version=1.8 user.name=xiongwei java.class.path=/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/charsets.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/deploy.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/cldrdata.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/dnsns.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/jaccess.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/jfxrt.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/localedata.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/nashorn.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunec.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext/zipfs.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/javaws.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jce.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jfr.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jfxswt.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jsse.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/management-agent.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/plugin.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/resources.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/rt.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/ant-javafx.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/dt.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/javafx-mx.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/jconsole.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/packager.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/sa-jdi.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/lib/tools.jar\:/Users/xiongwei/Documents/workspace/IntelliJSpace/jvm_lectue/out/production/classes\:/Users/xiongwei/.gradle/caches/modules-2/files-2.1/mysql/mysql-connector-java/5.1.34/46deba4adbdb4967367b013cbc67b7f7373da60a/mysql-connector-java-5.1.34.jar\:/Users/xiongwei/.gradle/caches/modules-2/files-2.1/cglib/cglib/3.2.0/bced5c83ed985c080a24dc5a42b0ca631556f413/cglib-3.2.0.jar\:/Users/xiongwei/.gradle/caches/modules-2/files-2.1/org.ow2.asm/asm/5.0.3/dcc2193db20e19e1feca8b1240dbbc4e190824fa/asm-5.0.3.jar\:/Users/xiongwei/.gradle/caches/modules-2/files-2.1/org.apache.ant/ant/1.9.4/6d473e8653d952045f550f4ef225a9591b79094a/ant-1.9.4.jar\:/Users/xiongwei/.gradle/caches/modules-2/files-2.1/org.apache.ant/ant-launcher/1.9.4/334b62cb4be0432769679e8b94e83f8fd5ed395c/ant-launcher-1.9.4.jar java.vm.specification.version=1.8 sun.java.command=com.jvm.memory.MyTest5 java.home=/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre sun.arch.data.model=64 user.language=zh java.specification.vendor=Oracle Corporation user.language.format=en awt.toolkit=sun.lwawt.macosx.LWCToolkit java.vm.info=mixed mode java.version=1.8.0_92 java.ext.dirs=/Users/xiongwei/Library/Java/Extensions\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/ext\:/Library/Java/Extensions\:/Network/Library/Java/Extensions\:/System/Library/Java/Extensions\:/usr/lib/java sun.boot.class.path=/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/resources.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/rt.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/sunrsasign.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jsse.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jce.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/charsets.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/jfr.jar\:/Library/Java/JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/classes java.vendor=Oracle Corporation file.separator=/ java.vendor.url.bug=http\://bugreport.sun.com/bugreport/ sun.io.unicode.encoding=UnicodeBig sun.cpu.endian=little sun.cpu.isalist=
jcmd pid VM.version：查看JVM的版本信息。
jcmd pid VM.command_line：查看JVM启动的命令行参数信息。
以上就是关于jcmd的一些重要参数的演练，目前是纯练，记录下来待未来有需要时再回来翻阅。
