Questions posed online demonstrate the occasional desire of developers to access via their Java applications the types of information normally gained from running JConsole, VisualVM, or JDK command-line tools externally against the application. Here are some examples of those types of questions:
- How to get jmap histogram programmatically?
- Programmatically dumping heap from Java applications
- find which type of garbage collector is running
I recently blogged on the usefulness of jcmd. This “Swiss-army knife” of command-line JDK tools provides much information about running Java processes and many of the types of information developers might want to acquire programatically are available via jcmd.
The Tools Enhancements in JDK 8 page states, “JDK 8 provides remote access to diagnostic commands which were previously accessible only locally via the jcmd tool. Remote access is provided using the Java Management Extensions (JMX), so diagnostic commands are exposed to a platform MBean registered to the platform MBean server. The MBean is the com.sun.management.DiagnosticCommandMBean interface.” In the post Looking at DiagnosticCommandMBean in JConsole and VisualVM, I looked at using JMX and DiagnosticCommandMBean via JConsole and VisualVM to access jcmd type information on a running JVM process.
In this post I look at how to use com.sun.management.DiagnosticCommandMBean to programmatically access information provided by jcmd.
The DiagnosticCommandMBean is accessed via JMX using the ObjectName “com.sun.management:type=DiagnosticCommand“. Most of the operations require no arguments and return a String. With this in mind, a general approach to accessing these operations that have String[] signatures, a String return type, and don’t actually require a parameter is shown in the following code snippet.
Setting Up DiagnosticCommandMBean and General Method for Accessing Operations of Same Signature
/** 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;
}With the code above in place, the method invokeNoStringArgumentsCommand(String, String) can be used to access several of the operations that DiagnosticCommandMBean provides. The help sub-command is useful when used with jcmd because it lists the available sub-commands associated with a specified Java process. Likewise, the “help” operation provided by the DiagnosticCommandMBean is similarly helpful in providing a list of commands that the MBean supports. This is easy to access with the code shown next that uses the code just shown.
/**
* Provide list of supported operations (help).
*
* @return Single string containing names of supported operations.
*/
public String getAvailableOperations()
{
return invokeNoStringArgumentsCommand("help", "Help (List Commands)");
}Running this from a simple Java application leads to output similar to that shown next:
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 help For more information about a specific command use 'help '.
In my blog post Determining the Active HotSpot Garbage Collector, I wrote that jcmd can be used to identify the VM flags of a running Java process and that, from those flags, one can glean which garbage collector is in use. Because the DiagnosticCommandMBean supports the VM.flags operation as shown above, this operation can be used to view the VM flags and, from those flags, determine which collector is in use. The next code listing shows two example methods with the first accessing the VM flags of the process and the second method providing a simplistic example of how to use the first method to identify the garbage collector in use.
Obtain Virtual Machine Flags and Identify Active Garbage Collector
/**
* 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;
}The String with the VM flags and the output of the identified garbage collector are shown next:
-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:+UseParallelGC
Parallel/Throughput
The examples already shown (accessing help and VM flags) are demonstrative of the same general approach that can be used to programmatically access other operations on DiagnosticCommandMBean with the same signature. A series of code listings and corresponding output are shown next to illustrate some of these.
Accessing Virtual Machine Uptime
/**
* 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
Accessing Thread Dump
/**
* 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: RUNNABLE at 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: RUNNABLE at 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
Getting Class Histogram
/**
* 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 [C 2: 467 124976 [B 3: 992 104200 java.lang.Class 4: 3452 82848 java.lang.String 5: 1006 46744 [Ljava.lang.Object; 6: 525 46200 java.lang.reflect.Method 7: 309 22248 java.lang.reflect.Field 8: 519 16608 java.util.HashMap$Node 9: 326 11760 [Ljava.lang.String; 10: 211 8968 [I 11: 434 8312 [Ljava.lang.Class; 12: 77 7416 [Ljava.util.HashMap$Node; 13: 179 7160 java.lang.ref.SoftReference 14: 101 5656 java.lang.Class$ReflectionData 15: 73 4672 java.net.URL 16: 97 4656 java.util.HashMap 17: 89 4560 [Ljava.lang.reflect.Method; 18: 189 4536 javax.management.ImmutableDescriptor 19: 279 4464 java.lang.Integer 20: 139 4448 java.util.Hashtable$Entry 21: 105 4200 java.util.WeakHashMap$Entry 22: 129 4128 java.util.concurrent.ConcurrentHashMap$Node 23: 128 4096 com.sun.jmx.mbeanserver.ConvertingMethod 24: 90 3600 java.util.TreeMap$Entry 25: 34 3360 [Ljava.util.WeakHashMap$Entry; 26: 8 3008 java.lang.Thread 27: 45 2880 javax.management.openmbean.OpenMBeanAttributeInfoSupport 28: 87 2784 java.lang.ref.WeakReference 29: 160 2560 java.lang.Object 30: 49 2544 [Ljavax.management.MBeanAttributeInfo; 31: 135 2536 [Lcom.sun.jmx.mbeanserver.MXBeanMapping; 32: 30 2400 java.lang.reflect.Constructor 33: 48 2304 javax.management.MBeanInfo 34: 49 1960 java.io.ObjectStreamField 35: 60 1920 javax.management.MBeanAttributeInfo 36: 46 1840 java.util.LinkedHashMap$Entry 37: 38 1824 sun.util.locale.LocaleObjectCache$CacheEntry 38: 44 1760 java.lang.ref.Finalizer 39: 30 1752 [Ljava.lang.reflect.Field; 40: 36 1728 sun.misc.URLClassPath$JarLoader 41: 1 1712 [[B 42: 40 1600 sun.management.DiagnosticCommandArgumentInfo 43: 31 1488 java.util.WeakHashMap 44: 60 1440 java.util.ArrayList 45: 11 1392 [Ljava.util.Hashtable$Entry; 46: 42 1344 java.lang.ref.ReferenceQueue 47: 2 1320 [J 48: 10 1312 [Ljava.util.concurrent.ConcurrentHashMap$Node; 49: 26 1248 java.util.logging.LogManager$LoggerWeakRef 50: 47 1120 [Ljavax.management.ObjectName$Property; 51: 1 1040 [Ljava.lang.Integer; 52: 39 1008 [Ljavax.management.MBeanOperationInfo; 53: 24 960 javax.management.ObjectName 54: 38 912 java.io.ExpiringCache$Entry 55: 19 912 sun.management.DiagnosticCommandInfo 56: 18 864 java.util.TreeMap 57: 12 864 java.util.logging.Logger 58: 35 840 javax.management.ObjectName$Property 59: 15 840 javax.management.openmbean.ArrayType 60: 20 800 com.sun.jmx.mbeanserver.MXBeanSupport 61: 20 800 javax.management.MBeanOperationInfo 62: 14 784 sun.nio.cs.UTF_8$Encoder 63: 32 768 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$IdentityMapping 64: 12 768 java.util.jar.JarFile 65: 19 760 sun.util.locale.BaseLocale$Key 66: 15 720 java.lang.management.PlatformComponent 67: 44 704 java.lang.ref.ReferenceQueue$Lock 68: 11 704 java.util.concurrent.ConcurrentHashMap 69: 21 672 com.sun.jmx.mbeanserver.WeakIdentityHashMap$IdentityWeakReference 70: 7 672 java.util.jar.JarFile$JarFileEntry 71: 12 672 java.util.zip.ZipFile$ZipFileInputStream 72: 19 608 java.util.Locale 73: 19 608 sun.management.DiagnosticCommandImpl$Wrapper 74: 19 608 sun.util.locale.BaseLocale 75: 18 576 javax.management.MBeanParameterInfo 76: 10 560 java.util.LinkedHashMap 77: 14 560 javax.management.openmbean.SimpleType 78: 23 552 com.sun.jmx.mbeanserver.PerInterface$MethodAndSig 79: 26 536 [Ljava.lang.reflect.Constructor; 80: 22 528 com.sun.jmx.mbeanserver.NamedObject 81: 22 528 sun.reflect.generics.tree.SimpleClassTypeSignature 82: 13 520 java.security.AccessControlContext 83: 16 512 java.util.logging.LogManager$LogNode 84: 17 504 [Ljava.io.ObjectStreamField; 85: 9 504 javax.management.openmbean.CompositeType 86: 19 488 [Lsun.management.DiagnosticCommandArgumentInfo; 87: 12 480 com.sun.jmx.mbeanserver.PerInterface 88: 20 480 java.lang.Class$AnnotationData 89: 20 480 java.util.Arrays$ArrayList 90: 20 480 java.util.jar.Attributes$Name 91: 19 456 [Ljavax.management.MBeanParameterInfo; 92: 19 456 java.util.Locale$LocaleKey 93: 14 448 java.util.concurrent.locks.ReentrantLock$NonfairSync 94: 8 448 javax.management.openmbean.OpenMBeanParameterInfoSupport 95: 20 440 [Ljavax.management.MBeanNotificationInfo; 96: 13 416 java.io.File 97: 22 408 [Lsun.reflect.generics.tree.TypeArgument; 98: 10 400 java.io.FileDescriptor 99: 10 400 sun.reflect.UnsafeQualifiedStaticObjectFieldAccessorImpl 100: 1 384 java.lang.ref.Finalizer$FinalizerThread 101: 6 384 java.nio.DirectByteBuffer 102: 8 384 java.util.Hashtable 103: 1 384 java.util.logging.LogManager$Cleaner 104: 12 384 java.util.zip.ZipCoder 105: 1 376 java.lang.ref.Reference$ReferenceHandler 106: 15 360 javax.management.StandardMBean 107: 22 352 sun.reflect.generics.tree.ClassTypeSignature 108: 4 336 [D 109: 7 336 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$CompositeMapping 110: 6 336 java.nio.DirectLongBufferU 111: 14 336 java.util.concurrent.CopyOnWriteArrayList 112: 6 336 sun.management.MemoryPoolImpl 113: 14 336 sun.reflect.NativeConstructorAccessorImpl 114: 16 328 [Ljava.lang.management.PlatformComponent; 115: 4 320 [S 116: 13 312 java.lang.management.ManagementPermission 117: 9 288 java.lang.OutOfMemoryError 118: 12 288 java.util.ArrayDeque 119: 12 288 java.util.Collections$SingletonList 120: 9 288 java.util.logging.Level 121: 12 288 sun.misc.MetaIndex 122: 5 280 sun.util.calendar.ZoneInfo 123: 8 256 sun.misc.ProxyGenerator$PrimitiveTypeInfo 124: 2 240 java.net.SocksSocketImpl 125: 6 240 sun.management.MemoryPoolImpl$CollectionSensor 126: 6 240 sun.management.MemoryPoolImpl$PoolSensor 127: 6 240 sun.reflect.generics.repository.MethodRepository 128: 14 224 java.util.concurrent.locks.ReentrantLock 129: 14 224 sun.reflect.DelegatingConstructorAccessorImpl 130: 13 216 [Ljavax.management.MBeanConstructorInfo; 131: 9 216 java.util.logging.Level$KnownLevel 132: 9 216 sun.util.logging.PlatformLogger$Level 133: 10 208 [Ljava.lang.reflect.Type; 134: 5 200 java.lang.ClassLoader$NativeLibrary 135: 6 192 java.util.Vector 136: 8 192 sun.reflect.generics.factory.CoreReflectionFactory 137: 6 192 sun.reflect.generics.tree.MethodTypeSignature 138: 2 176 java.net.DualStackPlainSocketImpl 139: 9 168 [Lsun.reflect.generics.tree.FieldTypeSignature; 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162: 3 96 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$EnumMapping 163: 4 96 java.lang.RuntimePermission 164: 2 96 java.lang.ThreadGroup 165: 6 96 java.lang.ThreadLocal 166: 2 96 java.nio.HeapByteBuffer 167: 4 96 java.util.Collections$UnmodifiableRandomAccessList 168: 3 96 java.util.Stack 169: 2 96 java.util.zip.Inflater 170: 2 96 javax.management.openmbean.TabularType 171: 2 96 sun.management.GarbageCollectorImpl 172: 2 96 sun.nio.cs.StreamEncoder 173: 4 96 sun.reflect.annotation.AnnotationInvocationHandler 174: 3 96 sun.reflect.generics.reflectiveObjects.TypeVariableImpl 175: 3 96 sun.reflect.generics.repository.ClassRepository 176: 1 88 sun.misc.Launcher$AppClassLoader 177: 1 88 sun.misc.Launcher$ExtClassLoader 178: 1 80 [Ljava.lang.ThreadLocal$ThreadLocalMap$Entry; 179: 1 80 [Ljava.lang.invoke.LambdaForm; 180: 2 80 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory$TabularMapping 181: 2 80 java.io.BufferedWriter 182: 2 80 java.io.ExpiringCache 183: 2 80 java.lang.invoke.MethodType 184: 2 80 java.util.IdentityHashMap 185: 2 80 sun.management.MemoryManagerImpl 186: 2 80 sun.misc.FloatingDecimal$BinaryToASCIIBuffer 187: 2 80 sun.misc.URLClassPath 188: 1 72 [Ljavax.management.openmbean.SimpleType; 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252: 1 40 [Ljava.lang.management.MemoryPoolMXBean; 253: 1 40 com.sun.jmx.interceptor.DefaultMBeanServerInterceptor 254: 1 40 com.sun.jmx.mbeanserver.JmxMBeanServer 255: 1 40 com.sun.jmx.mbeanserver.MBeanServerDelegateImpl 256: 1 40 java.io.BufferedInputStream 257: 1 40 sun.management.DiagnosticCommandImpl 258: 1 40 sun.nio.cs.StandardCharsets$Aliases 259: 1 40 sun.nio.cs.StandardCharsets$Cache 260: 1 40 sun.nio.cs.StandardCharsets$Classes 261: 1 40 sun.nio.cs.UTF_8$Decoder 262: 1 32 [Ljava.lang.OutOfMemoryError; 263: 2 32 [Ljava.lang.StackTraceElement; 264: 1 32 [Ljava.lang.ThreadGroup; 265: 1 32 [Ljava.lang.management.MemoryManagerMXBean; 266: 1 32 com.sun.jmx.mbeanserver.Repository 267: 1 32 java.io.WinNTFileSystem 268: 1 32 java.lang.ArithmeticException 269: 2 32 java.lang.Boolean 270: 1 32 java.lang.NullPointerException 271: 2 32 java.lang.Shutdown$Lock 272: 1 32 java.lang.StringCoding$StringDecoder 273: 1 32 java.lang.reflect.WeakCache 274: 1 32 java.net.Socket 275: 2 32 java.nio.ByteOrder 276: 1 32 java.util.Collections$UnmodifiableMap 277: 2 32 java.util.HashMap$EntrySet 278: 1 32 java.util.concurrent.atomic.AtomicReferenceFieldUpdater$AtomicReferenceFieldUpdaterImpl 279: 1 32 java.util.logging.LogManager$SystemLoggerContext 280: 1 32 javax.management.MBeanConstructorInfo 281: 1 32 sun.management.MemoryImpl 282: 2 32 sun.net.www.protocol.jar.Handler 283: 1 32 sun.nio.cs.StandardCharsets 284: 1 24 [Ljava.io.File$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.ClassLoaderRepositorySupport 291: 1 24 com.sun.jmx.mbeanserver.MXBeanLookup 292: 1 24 com.sun.jmx.remote.util.ClassLogger 293: 1 24 dustin.examples.diagnostics.VirtualMachineDiagnostics 294: 1 24 java.lang.ThreadLocal$ThreadLocalMap 295: 1 24 java.lang.invoke.LambdaForm$NamedFunction 296: 1 24 java.lang.invoke.MethodType$ConcurrentWeakInternSet 297: 1 24 java.lang.reflect.ReflectPermission 298: 1 24 java.net.Inet4Address 299: 1 24 java.net.Inet6AddressImpl 300: 1 24 java.net.ServerSocket 301: 1 24 java.util.BitSet 302: 1 24 java.util.Collections$EmptyMap 303: 1 24 java.util.Collections$SetFromMap 304: 1 24 java.util.Locale$Cache 305: 1 24 java.util.concurrent.atomic.AtomicLong 306: 1 24 java.util.concurrent.locks.ReentrantReadWriteLock 307: 1 24 java.util.jar.Manifest 308: 1 24 java.util.logging.LogManager$LoggerContext 309: 1 24 java.util.logging.LoggingPermission 310: 1 24 javax.management.NotificationBroadcasterSupport 311: 1 24 sun.launcher.LauncherHelper 312: 1 24 sun.management.CompilationImpl 313: 1 24 sun.management.OperatingSystemImpl 314: 1 24 sun.management.RuntimeImpl 315: 1 24 sun.management.ThreadImpl 316: 1 24 sun.management.VMManagementImpl 317: 1 24 sun.misc.JarIndex 318: 1 24 sun.misc.URLClassPath$FileLoader 319: 1 24 sun.nio.cs.ISO_8859_1 320: 1 24 sun.nio.cs.MS1252 321: 1 24 sun.nio.cs.ThreadLocalCoders$1 322: 1 24 sun.nio.cs.ThreadLocalCoders$2 323: 1 24 sun.nio.cs.US_ASCII 324: 1 24 sun.nio.cs.UTF_16 325: 1 24 sun.nio.cs.UTF_16BE 326: 1 24 sun.nio.cs.UTF_16LE 327: 1 24 sun.nio.cs.UTF_8 328: 1 24 sun.util.locale.BaseLocale$Cache 329: 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$1 334: 1 16 com.sun.jmx.interceptor.DefaultMBeanServerInterceptor$ResourceContext$1 335: 1 16 com.sun.jmx.mbeanserver.DefaultMXBeanMappingFactory 336: 1 16 com.sun.jmx.mbeanserver.DescriptorCache 337: 1 16 com.sun.jmx.mbeanserver.MBeanAnalyzer$MethodOrder 338: 1 16 com.sun.jmx.mbeanserver.MBeanInstantiator 339: 1 16 com.sun.jmx.mbeanserver.MXBeanIntrospector 340: 1 16 com.sun.jmx.mbeanserver.SecureClassLoaderRepository 341: 1 16 java.io.FileDescriptor$1 342: 1 16 java.lang.ApplicationShutdownHooks$1 343: 1 16 java.lang.CharacterDataLatin1 344: 1 16 java.lang.Runtime 345: 1 16 java.lang.String$CaseInsensitiveComparator 346: 1 16 java.lang.System$2 347: 1 16 java.lang.Terminator$1 348: 1 16 java.lang.invoke.MemberName$Factory 349: 1 16 java.lang.management.PlatformComponent$1 350: 1 16 java.lang.management.PlatformComponent$10 351: 1 16 java.lang.management.PlatformComponent$11 352: 1 16 java.lang.management.PlatformComponent$12 353: 1 16 java.lang.management.PlatformComponent$13 354: 1 16 java.lang.management.PlatformComponent$14 355: 1 16 java.lang.management.PlatformComponent$15 356: 1 16 java.lang.management.PlatformComponent$2 357: 1 16 java.lang.management.PlatformComponent$3 358: 1 16 java.lang.management.PlatformComponent$4 359: 1 16 java.lang.management.PlatformComponent$5 360: 1 16 java.lang.management.PlatformComponent$6 361: 1 16 java.lang.management.PlatformComponent$7 362: 1 16 java.lang.management.PlatformComponent$8 363: 1 16 java.lang.management.PlatformComponent$9 364: 1 16 java.lang.ref.Reference$Lock 365: 1 16 java.lang.reflect.Proxy$KeyFactory 366: 1 16 java.lang.reflect.Proxy$ProxyClassFactory 367: 1 16 java.lang.reflect.ReflectAccess 368: 1 16 java.net.InetAddress$2 369: 1 16 java.net.URLClassLoader$7 370: 1 16 java.nio.Bits$1 371: 1 16 java.nio.Bits$1$1 372: 1 16 java.nio.charset.CoderResult$1 373: 1 16 java.nio.charset.CoderResult$2 374: 1 16 java.security.ProtectionDomain$1 375: 1 16 java.security.ProtectionDomain$3 376: 1 16 java.util.Collections$EmptyIterator 377: 1 16 java.util.Collections$EmptyList 378: 1 16 java.util.Collections$EmptySet 379: 1 16 java.util.Collections$SingletonSet 380: 1 16 java.util.HashMap$Values 381: 1 16 java.util.Hashtable$EntrySet 382: 1 16 java.util.WeakHashMap$KeySet 383: 1 16 java.util.concurrent.atomic.AtomicInteger 384: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock 385: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$Sync$ThreadLocalHoldCounter 386: 1 16 java.util.concurrent.locks.ReentrantReadWriteLock$WriteLock 387: 1 16 java.util.jar.Attributes 388: 1 16 java.util.jar.JavaUtilJarAccessImpl 389: 1 16 java.util.logging.LoggingProxyImpl 390: 1 16 java.util.zip.ZipFile$1 391: 1 16 javax.management.JMX 392: 1 16 javax.management.MBeanServerBuilder 393: 1 16 javax.management.NotificationBroadcasterSupport$1 394: 1 16 sun.management.ClassLoadingImpl 395: 1 16 sun.management.HotSpotDiagnostic 396: 1 16 sun.management.ManagementFactoryHelper$PlatformLoggingImpl 397: 1 16 sun.misc.ASCIICaseInsensitiveComparator 398: 1 16 sun.misc.FloatingDecimal$1 399: 1 16 sun.misc.Launcher 400: 1 16 sun.misc.Launcher$Factory 401: 1 16 sun.misc.Perf 402: 1 16 sun.misc.Unsafe 403: 1 16 sun.net.www.protocol.file.Handler 404: 1 16 sun.nio.ch.FileChannelImpl$1 405: 1 16 sun.reflect.ReflectionFactory 406: 1 16 sun.reflect.generics.tree.TypeVariableSignature 407: 1 16 sun.util.calendar.Gregorian Total 16267 885480
Some of the sub-commands available with jcmd are only available when diagnostic operations are unlocked with -XX:+UnlockDiagnosticVMOptions (specified when running the Java process). This is true of the DiagnosticCommandMBean counterparts as demonstrated in the next code listing and output listing.
Accessing Class Statistics
/**
* 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
One jcmd subcommand I have not seen exposed as an operation on DiagnosticCommandMBean is that for generating a heap dump (jcmd‘s GC.heap_dump). There is no equivalent operation exposed by DiagnosticCommandMBean as far as I can tell from looking at the exposed operations in VisualVM and JConsole and from looking at the available commands listed by the “help” operation as demonstrated above. Although DiagnosticCommandMBean does not appear to provide an operation for invoking a heap dump, another MBean (com.sun.management.HotSpotDiagnostic with ObjectName of “com.sun.management:type=HotSpotDiagnostic”) does with operation “dumpHeap” and this is demonstrated in A. Sundararajan‘s’s blog post “Programmatically dumping heap from Java applications.”
Conclusion
The DiagnosticCommandMBean provides most of jcmd‘s functionality and it therefore makes jcmd functionality available to Java applications to run that functionality against themselves.
The code listings shown in this post are available in the class VirtualMachineDiagnostics, which is available on GitHub. I may add or modify this class in the future, but the original version has the same code as shown in this post.
| Reference: | Programmatic jcmd Access from our JCG partner Dustin Marx at the Inspired by Actual Events blog. |
