jcmd

在線提出的問題表明，開發人員偶爾會希望通過Java應用程序訪問通常從針對應用程序外部運行JConsole ， VisualVM或JDK命令行工具獲得的信息類型。 以下是這類問題的一些示例：

• 如何以編程方式獲取jmap直方圖？
• 以編程方式從Java應用程序中轉儲堆
• 查找運行哪種類型的垃圾收集器

我最近在博客上介紹了 jcmd 的用處 。 命令行JDK工具的“ 瑞士軍刀 ”提供了有關運行Java進程的許多信息，并且開發人員可能希望通過編程方式獲取的許多類型的信息都可以通過jcmd 。

“ JDK 8頁面上的工具增強 ”指出：“ JDK 8提供了對診斷命令的遠程訪問，以前只能通過jcmd工具在本地訪問這些診斷命令。 使用Java管理擴展（JMX）提供了遠程訪問，因此診斷命令將向注冊到平臺MBean服務器的平臺MBean公開。 MBean是com.sun.management.DiagnosticCommandMBean接口。” 在“ 在JConsole和VisualVM中查看DiagnosticCommandMBean”一文中 ，我研究了如何通過JConsole和VisualVM使用JMX和DiagnosticCommandMBean在運行中的JVM進程上訪問jcmd類型信息。

在這篇文章中我看看如何使用com.sun.management.DiagnosticCommandMBean以編程方式訪問信息提供jcmd 。

通過JMX使用ObjectName “ com.sun.management:type=DiagnosticCommand ”訪問DiagnosticCommandMBean 。 大多數操作不需要參數，并返回String 。 考慮到這一點，下面的代碼片段展示了一種訪問具有String[]簽名， String返回類型且實際上不需要參數的操作的通用方法。

設置DiagnosticCommandMBean和訪問相同簽名操作的通用方法

/** Object Name of DiagnosticCommandMBean. */public final static String DIAGNOSTIC_COMMAND_MBEAN_NAME ="com.sun.management:type=DiagnosticCommand";/** My MBean Server. */private final MBeanServer server = ManagementFactory.getPlatformMBeanServer();/** Platform MBean Server. */private final ObjectName objectName;// . . ./*** Invoke operation on the DiagnosticCommandMBean that accepts* String array argument but does not require any String* argument and returns a String.** @param operationName Name of operation on DiagnosticCommandMBean.* @param operationDescription Description of operation being invoked* on the DiagnosticCommandMBean.* @return String returned by DiagnosticCommandMBean operation.*/private String invokeNoStringArgumentsCommand(final String operationName, final String operationDescription){String result;try{result = (String) server.invoke(objectName, operationName, new Object[] {null}, new String[]{String[].class.getName()});}catch (InstanceNotFoundException | ReflectionException | MBeanException exception){result = "ERROR: Unable to access '" + operationDescription + "' - " + exception;}return result;}

使用上面的代碼，方法invokeNoStringArgumentsCommand(String, String)可以用于訪問DiagnosticCommandMBean提供的一些操作。 與jcmd一起使用時， help子命令很有用，因為它列出了與指定Java進程關聯的可用子命令。 同樣， DiagnosticCommandMBean提供的“幫助”操作在提供MBean支持的命令列表方面同樣有幫助。 使用下面顯示的代碼（使用剛剛顯示的代碼）可以輕松訪問此代碼。

/*** Provide list of supported operations (help).** @return Single string containing names of supported operations.*/ public String getAvailableOperations() {return invokeNoStringArgumentsCommand("help", "Help (List Commands)"); }

從一個簡單的Java應用程序運行它會導致輸出類似于下圖所示：

The following commands are available: JFR.stop JFR.start JFR.dump JFR.check VM.native_memory VM.check_commercial_features VM.unlock_commercial_features GC.rotate_log Thread.print GC.class_stats GC.class_histogram GC.run_finalization GC.run VM.uptime VM.flags VM.system_properties VM.command_line VM.version helpFor more information about a specific command use 'help '.

在我的博客文章“ 確定活動的HotSpot垃圾收集器”中 ，我寫道jcmd可用于標識正在運行的Java進程的VM標志，并且可以從這些標志中收集正在使用的垃圾收集器。 因為DiagnosticCommandMBean支持如上所述的VM.flags操作，所以該操作可用于查看VM標志并從這些標志中確定正在使用哪個收集器。 下一個代碼清單顯示了兩個示例方法，第一個方法訪問進程的VM標志，第二個方法提供了如何使用第一個方法來標識正在使用的垃圾收集器的簡單示例。

獲取虛擬機標志并標識活動垃圾收集器

/*** Provide a String representing the Virtual Machine flags.** @return String containing the virtual machine flags.*/ public String getVirtualMachineFlags() {return invokeNoStringArgumentsCommand("vmFlags", "Determine VM flags"); }/*** Provide String representing active/current garbage collector.** @return String representation of current garbage collector* ("Parallel/Throughput", "Concurrent Mark Sweep (CMS)",* "Garbage First", or "UNDETERMINED").*/ public String determineGarbageCollector() {String garbageCollector;final String vmFlags = getVirtualMachineFlags();if (vmFlags.contains("+UseParallelGC") || vmFlags.contains("+UseParallelOldGC")){garbageCollector = "Parallel/Throughput";}else if (vmFlags.contains("+UseConcMarkSweepGC")){garbageCollector = "Concurrent Mark Sweep (CMS)";}else if (vmFlags.contains("+UseG1GC")){garbageCollector = "Garbage First";}else{garbageCollector = "UNDETERMINED";}return garbageCollector; }

接下來顯示帶有VM標志的字符串和已標識的垃圾收集器的輸出：

-XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2128609280 -XX:MaxNewSize=709361664 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGCParallel/Throughput

已經顯示的示例（訪問幫助和VM標志）說明了相同的通用方法，該方法可用于以編程方式訪問具有相同簽名的DiagnosticCommandMBean上的其他操作。 接下來顯示一系列代碼清單和相應的輸出以說明其中的一些。

訪問虛擬機正常運行時間

/*** Provide virtual machine uptime as single String.** @return Single string containing virtual machine uptime.*/ public String getVirtualMachineUptime() {return invokeNoStringArgumentsCommand("vmUptime", "Virtual Machine Uptime"); }0.272 s

訪問線程轉儲

/*** Provide thread dump as single String.** @return Single string containing formatted thread dump.*/ public String getThreadDump() {return invokeNoStringArgumentsCommand("threadPrint", "Thread Dump"); }2016-04-30 20:21:22 Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.25-b02 mixed mode):"Monitor Ctrl-Break" #10 daemon prio=5 os_prio=0 tid=0x00000000189ea800 nid=0x1590 runnable [0x000000001903e000]java.lang.Thread.State: RUNNABLEat java.net.DualStackPlainSocketImpl.accept0(Native Method)at java.net.DualStackPlainSocketImpl.socketAccept(DualStackPlainSocketImpl.java:131)at java.net.AbstractPlainSocketImpl.accept(AbstractPlainSocketImpl.java:404)at java.net.PlainSocketImpl.accept(PlainSocketImpl.java:199)- locked <0x0000000081208810> (a java.net.SocksSocketImpl)at java.net.ServerSocket.implAccept(ServerSocket.java:545)at java.net.ServerSocket.accept(ServerSocket.java:513)at com.intellij.rt.execution.application.AppMain$1.run(AppMain.java:90)at java.lang.Thread.run(Thread.java:745)"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x0000000018915800 nid=0x2468 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C1 CompilerThread2" #8 daemon prio=9 os_prio=2 tid=0x0000000017087000 nid=0x17a0 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread1" #7 daemon prio=9 os_prio=2 tid=0x0000000017080000 nid=0x1560 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"C2 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x000000001707d000 nid=0x2004 waiting on condition [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x000000001707b000 nid=0x2160 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x000000001707a000 nid=0x458 runnable [0x0000000000000000]java.lang.Thread.State: RUNNABLE"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x00000000024f7000 nid=0x1964 in Object.wait() [0x00000000183ef000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000081201570> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:142)- locked <0x0000000081201570> (a java.lang.ref.ReferenceQueue$Lock)at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:158)at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:209)"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x00000000024ee000 nid=0x270c in Object.wait() [0x00000000182ef000]java.lang.Thread.State: WAITING (on object monitor)at java.lang.Object.wait(Native Method)- waiting on <0x0000000081208c28> (a java.lang.ref.Reference$Lock)at java.lang.Object.wait(Object.java:502)at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:157)- locked <0x0000000081208c28> (a java.lang.ref.Reference$Lock)"main" #1 prio=5 os_prio=0 tid=0x0000000000c4e000 nid=0x24f8 waiting on condition [0x0000000000dee000]java.lang.Thread.State: RUNNABLEat sun.management.DiagnosticCommandImpl.executeDiagnosticCommand(Native Method)at sun.management.DiagnosticCommandImpl.access$000(DiagnosticCommandImpl.java:40)at sun.management.DiagnosticCommandImpl$Wrapper.execute(DiagnosticCommandImpl.java:128)at sun.management.DiagnosticCommandImpl.invoke(DiagnosticCommandImpl.java:230)at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819)at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801)at dustin.examples.diagnostics.VirtualMachineDiagnostics.invokeNoStringArgumentsCommand(VirtualMachineDiagnostics.java:167)at dustin.examples.diagnostics.VirtualMachineDiagnostics.getThreadDump(VirtualMachineDiagnostics.java:88)at dustin.examples.diagnostics.VirtualMachineDiagnostics.main(VirtualMachineDiagnostics.java:187)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:483)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)"VM Thread" os_prio=2 tid=0x0000000017046000 nid=0x22b0 runnable "GC task thread#0 (ParallelGC)" os_prio=0 tid=0x0000000002417800 nid=0x1580 runnable "GC task thread#1 (ParallelGC)" os_prio=0 tid=0x0000000002419000 nid=0x16d8 runnable "GC task thread#2 (ParallelGC)" os_prio=0 tid=0x000000000241a800 nid=0x177c runnable "GC task thread#3 (ParallelGC)" os_prio=0 tid=0x000000000241c800 nid=0x1974 runnable "VM Periodic Task Thread" os_prio=2 tid=0x0000000018918000 nid=0x10dc waiting on condition JNI global references: 15

獲取類直方圖

/*** Provide class histogram as single String.** @return Single string containing formatted class histogram.*/ public String getHistogram() {return invokeNoStringArgumentsCommand("gcClassHistogram", "GC Class Histogram"); }num #instances #bytes class name ----------------------------------------------1: 3485 243064 [C2: 467 124976 [B3: 992 104200 java.lang.Class4: 3452 82848 java.lang.String5: 1006 46744 [Ljava.lang.Object;6: 525 46200 java.lang.reflect.Method7: 309 22248 java.lang.reflect.Field8: 519 16608 java.util.HashMap$Node9: 326 11760 [Ljava.lang.String;10: 211 8968 [I11: 434 8312 [Ljava.lang.Class;12: 77 7416 [Ljava.util.HashMap$Node;13: 179 7160 java.lang.ref.SoftReference14: 101 5656 java.lang.Class$ReflectionData15: 73 4672 java.net.URL16: 97 4656 java.util.HashMap17: 89 4560 [Ljava.lang.reflect.Method;18: 189 4536 javax.management.ImmutableDescriptor19: 279 4464 java.lang.Integer20: 139 4448 java.util.Hashtable$Entry21: 105 4200 java.util.WeakHashMap$Entry22: 129 4128 java.util.concurrent.ConcurrentHashMap$Node23: 128 4096 com.sun.jmx.mbeanserver.ConvertingMethod24: 90 3600 java.util.TreeMap$Entry25: 34 3360 [Ljava.util.WeakHashMap$Entry;26: 8 3008 java.lang.Thread27: 45 2880 javax.management.openmbean.OpenMBeanAttributeInfoSupport28: 87 2784 java.lang.ref.WeakReference29: 160 2560 java.lang.Object30: 49 2544 [Ljavax.management.MBeanAttributeInfo;31: 135 2536 [Lcom.sun.jmx.mbeanserver.MXBeanMapping;32: 30 2400 java.lang.reflect.Constructor33: 48 2304 javax.management.MBeanInfo34: 49 1960 java.io.ObjectStreamField35: 60 1920 javax.management.MBeanAttributeInfo36: 46 1840 java.util.LinkedHashMap$Entry37: 38 1824 sun.util.locale.LocaleObjectCache$CacheEntry38: 44 1760 java.lang.ref.Finalizer39: 30 1752 [Ljava.lang.reflect.Field;40: 36 1728 sun.misc.URLClassPath$JarLoader41: 1 1712 [[B42: 40 1600 sun.management.DiagnosticCommandArgumentInfo43: 31 1488 java.util.WeakHashMap44: 60 1440 java.util.ArrayList45: 11 1392 [Ljava.util.Hashtable$Entry;46: 42 1344 java.lang.ref.ReferenceQueue47: 2 1320 [J48: 10 1312 [Ljava.util.concurrent.ConcurrentHashMap$Node;49: 26 1248 java.util.logging.LogManager$LoggerWeakRef50: 47 1120 [Ljavax.management.ObjectName$Property;51: 1 1040 [Ljava.lang.Integer;52: 39 1008 [Ljavax.management.MBeanOperationInfo;53: 24 960 javax.management.ObjectName54: 38 912 java.io.ExpiringCache$Entry55: 19 912 sun.management.DiagnosticCommandInfo56: 18 864 java.util.TreeMap57: 12 864 java.util.logging.Logger58: 35 840 javax.management.ObjectName$Property59: 15 840 javax.management.openmbean.ArrayType60: 20 800 com.sun.jmx.mbeanserver.MXBeanSupport61: 20 800 javax.management.MBeanOperationInfo62: 14 784 sun.nio.cs.UTF_8$Encoder63: 32 768 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$IdentityMapping64: 12 768 java.util.jar.JarFile65: 19 760 sun.util.locale.BaseLocale$Key66: 15 720 java.lang.management.PlatformComponent67: 44 704 java.lang.ref.ReferenceQueue$Lock68: 11 704 java.util.concurrent.ConcurrentHashMap69: 21 672 com.sun.jmx.mbeanserver.WeakIdentityHashMap$IdentityWeakReference70: 7 672 java.util.jar.JarFile$JarFileEntry71: 12 672 java.util.zip.ZipFile$ZipFileInputStream72: 19 608 java.util.Locale73: 19 608 sun.management.DiagnosticCommandImpl$Wrapper74: 19 608 sun.util.locale.BaseLocale75: 18 576 javax.management.MBeanParameterInfo76: 10 560 java.util.LinkedHashMap77: 14 560 javax.management.openmbean.SimpleType78: 23 552 com.sun.jmx.mbeanserver.PerInterface$MethodAndSig79: 26 536 [Ljava.lang.reflect.Constructor;80: 22 528 com.sun.jmx.mbeanserver.NamedObject81: 22 528 sun.reflect.generics.tree.SimpleClassTypeSignature82: 13 520 java.security.AccessControlContext83: 16 512 java.util.logging.LogManager$LogNode84: 17 504 [Ljava.io.ObjectStreamField;85: 9 504 javax.management.openmbean.CompositeType86: 19 488 [Lsun.management.DiagnosticCommandArgumentInfo;87: 12 480 com.sun.jmx.mbeanserver.PerInterface88: 20 480 java.lang.Class$AnnotationData89: 20 480 java.util.Arrays$ArrayList90: 20 480 java.util.jar.Attributes$Name91: 19 456 [Ljavax.management.MBeanParameterInfo;92: 19 456 java.util.Locale$LocaleKey93: 14 448 java.util.concurrent.locks.ReentrantLock$NonfairSync94: 8 448 javax.management.openmbean.OpenMBeanParameterInfoSupport95: 20 440 [Ljavax.management.MBeanNotificationInfo;96: 13 416 java.io.File97: 22 408 [Lsun.reflect.generics.tree.TypeArgument;98: 10 400 java.io.FileDescriptor99: 10 400 sun.reflect.UnsafeQualifiedStaticObjectFieldAccessorImpl100: 1 384 java.lang.ref.Finalizer$FinalizerThread101: 6 384 java.nio.DirectByteBuffer102: 8 384 java.util.Hashtable103: 1 384 java.util.logging.LogManager$Cleaner104: 12 384 java.util.zip.ZipCoder105: 1 376 java.lang.ref.Reference$ReferenceHandler106: 15 360 javax.management.StandardMBean107: 22 352 sun.reflect.generics.tree.ClassTypeSignature108: 4 336 [D109: 7 336 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$CompositeMapping110: 6 336 java.nio.DirectLongBufferU111: 14 336 java.util.concurrent.CopyOnWriteArrayList112: 6 336 sun.management.MemoryPoolImpl113: 14 336 sun.reflect.NativeConstructorAccessorImpl114: 16 328 [Ljava.lang.management.PlatformComponent;115: 4 320 [S116: 13 312 java.lang.management.ManagementPermission117: 9 288 java.lang.OutOfMemoryError118: 12 288 java.util.ArrayDeque119: 12 288 java.util.Collections$SingletonList120: 9 288 java.util.logging.Level121: 12 288 sun.misc.MetaIndex122: 5 280 sun.util.calendar.ZoneInfo123: 8 256 sun.misc.ProxyGenerator$PrimitiveTypeInfo124: 2 240 java.net.SocksSocketImpl125: 6 240 sun.management.MemoryPoolImpl$CollectionSensor126: 6 240 sun.management.MemoryPoolImpl$PoolSensor127: 6 240 sun.reflect.generics.repository.MethodRepository128: 14 224 java.util.concurrent.locks.ReentrantLock129: 14 224 sun.reflect.DelegatingConstructorAccessorImpl130: 13 216 [Ljavax.management.MBeanConstructorInfo;131: 9 216 java.util.logging.Level$KnownLevel132: 9 216 sun.util.logging.PlatformLogger$Level133: 10 208 [Ljava.lang.reflect.Type;134: 5 200 java.lang.ClassLoader$NativeLibrary135: 6 192 java.util.Vector136: 8 192 sun.reflect.generics.factory.CoreReflectionFactory137: 6 192 sun.reflect.generics.tree.MethodTypeSignature138: 2 176 java.net.DualStackPlainSocketImpl139: 9 168 [Lsun.reflect.generics.tree.FieldTypeSignature;140: 3 168 javax.management.openmbean.OpenMBeanOperationInfoSupport141: 9 160 [Lsun.reflect.generics.tree.FormalTypeParameter;142: 5 160 java.io.FileInputStream143: 4 160 java.security.ProtectionDomain144: 5 160 javax.management.MBeanNotificationInfo145: 5 160 javax.management.StandardEmitterMBean146: 6 144 java.util.LinkedList$Node147: 3 144 java.util.Properties148: 6 144 sun.misc.PerfCounter149: 6 144 sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl150: 6 144 sun.reflect.generics.scope.MethodScope151: 4 128 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$ArrayMapping152: 2 128 java.io.ExpiringCache$1153: 4 128 java.security.CodeSource154: 8 128 java.util.HashSet155: 4 128 java.util.LinkedList156: 1 120 [[Ljava.lang.String;157: 5 120 sun.misc.FloatingDecimal$PreparedASCIIToBinaryBuffer158: 2 112 java.lang.Package159: 2 112 java.util.zip.ZipFile$ZipFileInflaterInputStream160: 1 96 [Ljava.lang.invoke.MethodType;161: 6 96 [Lsun.reflect.generics.tree.TypeSignature;162: 3 96 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$EnumMapping163: 4 96 java.lang.RuntimePermission164: 2 96 java.lang.ThreadGroup165: 6 96 java.lang.ThreadLocal166: 2 96 java.nio.HeapByteBuffer167: 4 96 java.util.Collections$UnmodifiableRandomAccessList168: 3 96 java.util.Stack169: 2 96 java.util.zip.Inflater170: 2 96 javax.management.openmbean.TabularType171: 2 96 sun.management.GarbageCollectorImpl172: 2 96 sun.nio.cs.StreamEncoder173: 4 96 sun.reflect.annotation.AnnotationInvocationHandler174: 3 96 sun.reflect.generics.reflectiveObjects.TypeVariableImpl175: 3 96 sun.reflect.generics.repository.ClassRepository176: 1 88 sun.misc.Launcher$AppClassLoader177: 1 88 sun.misc.Launcher$ExtClassLoader178: 1 80 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry;179: 1 80 [Ljava.lang.invoke.LambdaForm;180: 2 80 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$TabularMapping181: 2 80 java.io.BufferedWriter182: 2 80 java.io.ExpiringCache183: 2 80 java.lang.invoke.MethodType184: 2 80 java.util.IdentityHashMap185: 2 80 sun.management.MemoryManagerImpl186: 2 80 sun.misc.FloatingDecimal$BinaryToASCIIBuffer187: 2 80 sun.misc.URLClassPath188: 1 72 [Ljavax.management.openmbean.SimpleType;189: 3 72 java.lang.annotation.RetentionPolicy190: 1 72 java.lang.invoke.MethodTypeForm191: 3 72 java.net.InetAddress$InetAddressHolder192: 3 72 java.util.Collections$SynchronizedSet193: 1 72 java.util.logging.LogManager$RootLogger194: 3 72 sun.misc.FloatingDecimal$ExceptionalBinaryToASCIIBuffer195: 3 72 sun.reflect.NativeMethodAccessorImpl196: 3 72 sun.reflect.generics.tree.ClassSignature197: 3 72 sun.reflect.generics.tree.FormalTypeParameter198: 1 64 [F199: 2 64 [Ljava.lang.Thread;200: 2 64 [Ljava.lang.annotation.RetentionPolicy;201: 4 64 [Ljava.security.Principal;202: 2 64 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$CollectionMapping203: 4 64 com.sun.proxy.$Proxy1204: 2 64 java.io.FileOutputStream205: 2 64 java.io.FilePermission206: 2 64 java.io.PrintStream207: 2 64 java.lang.ThreadLocal$ThreadLocalMap$Entry208: 2 64 java.lang.VirtualMachineError209: 2 64 java.lang.invoke.MethodType$ConcurrentWeakInternSet$WeakEntry210: 2 64 java.lang.ref.ReferenceQueue$Null211: 2 64 java.lang.reflect.Proxy$Key1212: 2 64 java.lang.reflect.WeakCache$CacheValue213: 2 64 java.security.BasicPermissionCollection214: 2 64 java.security.Permissions215: 4 64 java.security.ProtectionDomain$Key216: 4 64 java.util.LinkedHashMap$LinkedValues217: 2 64 java.util.PropertyPermission218: 2 64 sun.reflect.annotation.AnnotationType219: 1 56 [Ljava.lang.Runnable;220: 3 56 [Lsun.reflect.generics.tree.ClassTypeSignature;221: 1 56 [Lsun.util.logging.PlatformLogger$Level;222: 1 56 java.lang.invoke.MemberName223: 1 56 java.util.logging.LogManager224: 3 48 [Ljava.lang.annotation.Annotation;225: 2 48 [Ljava.lang.reflect.TypeVariable;226: 1 48 [[Ljava.lang.Object;227: 2 48 com.sun.jmx.mbeanserver.ClassLoaderRepositorySupport$LoaderEntry228: 1 48 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$Mappings229: 1 48 com.sun.jmx.mbeanserver.MBeanIntrospector$MBeanInfoMap230: 1 48 com.sun.jmx.mbeanserver.MBeanIntrospector$PerInterfaceMap231: 2 48 com.sun.jmx.mbeanserver.WeakIdentityHashMap232: 2 48 java.io.BufferedOutputStream233: 2 48 java.io.File$PathStatus234: 2 48 java.io.FilePermissionCollection235: 2 48 java.io.OutputStreamWriter236: 2 48 java.lang.StringBuilder237: 2 48 java.net.InetAddress238: 2 48 java.net.InetAddress$Cache239: 2 48 java.net.InetAddress$Cache$Type240: 2 48 java.nio.charset.CoderResult241: 3 48 java.nio.charset.CodingErrorAction242: 1 48 java.util.concurrent.locks.ReentrantReadWriteLock$FairSync243: 2 48 java.util.logging.Logger$LoggerBundle244: 2 48 java.util.zip.ZStreamRef245: 2 48 sun.management.ManagementFactoryHelper$1246: 2 48 sun.misc.NativeSignalHandler247: 2 48 sun.misc.Signal248: 1 48 sun.nio.cs.SingleByte$Decoder249: 3 48 sun.reflect.DelegatingMethodAccessorImpl250: 2 48 sun.reflect.generics.scope.ClassScope251: 2 40 [Lcom.sun.jmx.mbeanserver.ClassLoaderRepositorySupport$LoaderEntry;252: 1 40 [Ljava.lang.management.MemoryPoolMXBean;253: 1 40 com.sun.jmx.interceptor.DefaultMBeanServerInterceptor254: 1 40 com.sun.jmx.mbeanserver.JmxMBeanServer255: 1 40 com.sun.jmx.mbeanserver.MBeanServerDelegateImpl256: 1 40 java.io.BufferedInputStream257: 1 40 sun.management.DiagnosticCommandImpl258: 1 40 sun.nio.cs.StandardCharsets$Aliases259: 1 40 sun.nio.cs.StandardCharsets$Cache260: 1 40 sun.nio.cs.StandardCharsets$Classes261: 1 40 sun.nio.cs.UTF_8$Decoder262: 1 32 [Ljava.lang.OutOfMemoryError;263: 2 32 [Ljava.lang.StackTraceElement;264: 1 32 [Ljava.lang.ThreadGroup;265: 1 32 [Ljava.lang.management.MemoryManagerMXBean;266: 1 32 com.sun.jmx.mbeanserver.Repository267: 1 32 java.io.WinNTFileSystem268: 1 32 java.lang.ArithmeticException269: 2 32 java.lang.Boolean270: 1 32 java.lang.NullPointerException271: 2 32 java.lang.Shutdown$Lock272: 1 32 java.lang.StringCoding$StringDecoder273: 1 32 java.lang.reflect.WeakCache274: 1 32 java.net.Socket275: 2 32 java.nio.ByteOrder276: 1 32 java.util.Collections$UnmodifiableMap277: 2 32 java.util.HashMap$EntrySet278: 1 32 java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl279: 1 32 java.util.logging.LogManager$SystemLoggerContext280: 1 32 javax.management.MBeanConstructorInfo281: 1 32 sun.management.MemoryImpl282: 2 32 sun.net.www.protocol.jar.Handler283: 1 32 sun.nio.cs.StandardCharsets284: 1 24 [Ljava.io.File$PathStatus;285: 1 24 [Ljava.lang.invoke.MethodHandle;286: 1 24 [Ljava.net.InetAddress$Cache$Type;287: 1 24 [Ljava.net.InetSocketAddress;288: 1 24 [Ljava.security.ProtectionDomain;289: 1 24 [Lsun.launcher.LauncherHelper;290: 1 24 com.sun.jmx.mbeanserver.ClassLoaderRepositorySupport291: 1 24 com.sun.jmx.mbeanserver.MXBeanLookup292: 1 24 com.sun.jmx.remote.util.ClassLogger293: 1 24 dustin.examples.diagnostics.VirtualMachineDiagnostics294: 1 24 java.lang.ThreadLocal$ThreadLocalMap295: 1 24 java.lang.invoke.LambdaForm$NamedFunction296: 1 24 java.lang.invoke.MethodType$ConcurrentWeakInternSet297: 1 24 java.lang.reflect.ReflectPermission298: 1 24 java.net.Inet4Address299: 1 24 java.net.Inet6AddressImpl300: 1 24 java.net.ServerSocket301: 1 24 java.util.BitSet302: 1 24 java.util.Collections$EmptyMap303: 1 24 java.util.Collections$SetFromMap304: 1 24 java.util.Locale$Cache305: 1 24 java.util.concurrent.atomic.AtomicLong306: 1 24 java.util.concurrent.locks.ReentrantReadWriteLock307: 1 24 java.util.jar.Manifest308: 1 24 java.util.logging.LogManager$LoggerContext309: 1 24 java.util.logging.LoggingPermission310: 1 24 javax.management.NotificationBroadcasterSupport311: 1 24 sun.launcher.LauncherHelper312: 1 24 sun.management.CompilationImpl313: 1 24 sun.management.OperatingSystemImpl314: 1 24 sun.management.RuntimeImpl315: 1 24 sun.management.ThreadImpl316: 1 24 sun.management.VMManagementImpl317: 1 24 sun.misc.JarIndex318: 1 24 sun.misc.URLClassPath$FileLoader319: 1 24 sun.nio.cs.ISO_8859_1320: 1 24 sun.nio.cs.MS1252321: 1 24 sun.nio.cs.ThreadLocalCoders$1322: 1 24 sun.nio.cs.ThreadLocalCoders$2323: 1 24 sun.nio.cs.US_ASCII324: 1 24 sun.nio.cs.UTF_16325: 1 24 sun.nio.cs.UTF_16BE326: 1 24 sun.nio.cs.UTF_16LE327: 1 24 sun.nio.cs.UTF_8328: 1 24 sun.util.locale.BaseLocale$Cache329: 1 16 [Ljava.lang.Throwable;330: 1 16 [Ljava.nio.file.attribute.FileAttribute;331: 1 16 [Ljava.security.cert.Certificate;332: 1 16 [Ljava.util.logging.Handler;333: 1 16 com.intellij.rt.execution.application.AppMain$1334: 1 16 com.sun.jmx.interceptor.DefaultMBeanServerInterceptor$ResourceContext$1335: 1 16 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory336: 1 16 com.sun.jmx.mbeanserver.DescriptorCache337: 1 16 com.sun.jmx.mbeanserver.MBeanAnalyzer$MethodOrder338: 1 16 com.sun.jmx.mbeanserver.MBeanInstantiator339: 1 16 com.sun.jmx.mbeanserver.MXBeanIntrospector340: 1 16 com.sun.jmx.mbeanserver.SecureClassLoaderRepository341: 1 16 java.io.FileDescriptor$1342: 1 16 java.lang.ApplicationShutdownHooks$1343: 1 16 java.lang.CharacterDataLatin1344: 1 16 java.lang.Runtime345: 1 16 java.lang.String$CaseInsensitiveComparator346: 1 16 java.lang.System$2347: 1 16 java.lang.Terminator$1348: 1 16 java.lang.invoke.MemberName$Factory349: 1 16 java.lang.management.PlatformComponent$1350: 1 16 java.lang.management.PlatformComponent$10351: 1 16 java.lang.management.PlatformComponent$11352: 1 16 java.lang.management.PlatformComponent$12353: 1 16 java.lang.management.PlatformComponent$13354: 1 16 java.lang.management.PlatformComponent$14355: 1 16 java.lang.management.PlatformComponent$15356: 1 16 java.lang.management.PlatformComponent$2357: 1 16 java.lang.management.PlatformComponent$3358: 1 16 java.lang.management.PlatformComponent$4359: 1 16 java.lang.management.PlatformComponent$5360: 1 16 java.lang.management.PlatformComponent$6361: 1 16 java.lang.management.PlatformComponent$7362: 1 16 java.lang.management.PlatformComponent$8363: 1 16 java.lang.management.PlatformComponent$9364: 1 16 java.lang.ref.Reference$Lock365: 1 16 java.lang.reflect.Proxy$KeyFactory366: 1 16 java.lang.reflect.Proxy$ProxyClassFactory367: 1 16 java.lang.reflect.ReflectAccess368: 1 16 java.net.InetAddress$2369: 1 16 java.net.URLClassLoader$7370: 1 16 java.nio.Bits$1371: 1 16 java.nio.Bits$1$1372: 1 16 java.nio.charset.CoderResult$1373: 1 16 java.nio.charset.CoderResult$2374: 1 16 java.security.ProtectionDomain$1375: 1 16 java.security.ProtectionDomain$3376: 1 16 java.util.Collections$EmptyIterator377: 1 16 java.util.Collections$EmptyList378: 1 16 java.util.Collections$EmptySet379: 1 16 java.util.Collections$SingletonSet380: 1 16 java.util.HashMap$Values381: 1 16 java.util.Hashtable$EntrySet382: 1 16 java.util.WeakHashMap$KeySet383: 1 16 java.util.concurrent.atomic.AtomicInteger384: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock385: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$Sync$ThreadLocalHoldCounter386: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$WriteLock387: 1 16 java.util.jar.Attributes388: 1 16 java.util.jar.JavaUtilJarAccessImpl389: 1 16 java.util.logging.LoggingProxyImpl390: 1 16 java.util.zip.ZipFile$1391: 1 16 javax.management.JMX392: 1 16 javax.management.MBeanServerBuilder393: 1 16 javax.management.NotificationBroadcasterSupport$1394: 1 16 sun.management.ClassLoadingImpl395: 1 16 sun.management.HotSpotDiagnostic396: 1 16 sun.management.ManagementFactoryHelper$PlatformLoggingImpl397: 1 16 sun.misc.ASCIICaseInsensitiveComparator398: 1 16 sun.misc.FloatingDecimal$1399: 1 16 sun.misc.Launcher400: 1 16 sun.misc.Launcher$Factory401: 1 16 sun.misc.Perf402: 1 16 sun.misc.Unsafe403: 1 16 sun.net.www.protocol.file.Handler404: 1 16 sun.nio.ch.FileChannelImpl$1405: 1 16 sun.reflect.ReflectionFactory406: 1 16 sun.reflect.generics.tree.TypeVariableSignature407: 1 16 sun.util.calendar.Gregorian Total 16267 885480

jcmd可用的某些子命令僅在使用-XX：+ UnlockDiagnosticVMOptions （在運行Java進程時指定）解鎖診斷操作時才可用。 如下面的代碼列表和輸出列表所示，對于DiagnosticCommandMBean對應對象而言，這是正確的。

訪問班級統計

/*** Provide class statistics as single String.** This is only supported when {@code -XX:+UnlockDiagnosticVMOptions} is enabled.** @return Single string containing formatted class statistics.*/ public String getClassStatistics() {return invokeNoStringArgumentsCommand("gcClassStats", "GC Class Statistics"); }GC.class_stats command requires -XX:+UnlockDiagnosticVMOptions

我尚未看到對DiagnosticCommandMBean一個jcmd子命令是生jcmd子命令（ jcmd的GC.heap_dump ）。 據我所知，通過查看VisualVM和JConsole中公開的操作以及查看由上述“幫助”操作列出的可用命令， DiagnosticCommandMBean沒有公開任何等效操作。 盡管DiagnosticCommandMBean似乎沒有提供調用堆轉儲的操作，但是另一個MBean（對象名稱為com.sun.management:type=HotSpotDiagnostic的com.sun.management.HotSpotDiagnostic）與操作“ dumpHeap”一起使用，并對此進行了演示。在A. Sundararajan的博客文章“以編程方式從Java應用程序中轉儲堆 ”中。

結論

DiagnosticCommandMBean提供了jcmd的大多數功能，因此它使Java應用程序可以使用jcmd功能來針對自己運行該功能。

這篇文章中顯示的代碼清單可在GitHub上的類VirtualMachineDiagnostics 找到 。 我將來可能會添加或修改此類，但原始版本的代碼與本文中所示的相同。

翻譯自: https://www.javacodegeeks.com/2016/05/programmatic-jcmd-access.html

jcmd

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