JVM调优中经常用到的几个命令

jcmd-查找jvm进程信息

jcmd命令默认是查找jvm进程信息，也可以执行相关的jvm命令。

帮助信息

F:\soft\Java\jdk1.8\bin>jcmd -h
Usage: jcmd class> file>
   or: jcmd -l
   or: jcmd -h

  command must be a valid jcmd command for the selected jvm.
  Use the command "help" to see which commands are available.
  If the pid is 0, commands will be sent to all Java processes.
  The main class argument will be used to match (either partially
  or fully) the class used to start Java.
  If no options are given, lists Java processes (same as -p).

  PerfCounter.print display the counters exposed by this process
  -f  read and execute commands from the file
  -l  list JVM processes on the local machine
  -h  this help

使用实例 1

F:\soft\Java\jdk1.8\bin>jcmd
3068 sun.tools.jcmd.JCmd

使用示例 2

使用命令：

jcmd 9816 PerfCounter.print

可详细打印对应java进程的有效性能计数器(performance counters)。

9816:
java.ci.totalTime=106668
java.cls.loadedClasses=639
java.cls.sharedLoadedClasses=0
java.cls.sharedUnloadedClasses=0
java.cls.unloadedClasses=0
java.property.java.class.path="boss-1.0.1.jar"
java.property.java.endorsed.dirs="F:\soft\Java\jre1.8\lib\endorsed"
java.property.java.ext.dirs="F:\soft\Java\jre1.8\lib\ext;C:\Windows\Sun\Java\lib\ext"
java.property.java.home="F:\soft\Java\jre1.8"
java.property.java.library.path="C:\ProgramData\Oracle\Java\javapath;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:\ProgramData\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;D:\soft\svn\bin;F:\soft\Java\jdk1.8\bin;E:\DTool\sdk\platform-tools;E:\DTool\sdk\tools;%MAVEN_HOME%\bin;D:\apache-maven-3.3.9\bin;D:\soft\MySQL\MySQLServer\bin;D:\as\gradle\gradle-2.14.1\bin;H:\php56\;H:\php56\ext;H:\DownLoad\apache-ant-1.10.1\bin;F:\Program Files\Git\cmd;F:\Program Files\Git\mingw64\bin;F:\Program Files\Git\usr\bin;F:\Program Files\VisualSVN Server\bin;F:\soft\python3;F:\Program Files (x86)\AllWinnerTech\PhoenixSuit\;."
java.property.java.version="1.8.0_101"
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="25.101-b13"
java.rt.vmArgs=""
java.rt.vmFlags=""
java.threads.daemon=4
java.threads.live=11
java.threads.livePeak=11
java.threads.started=12
sun.ci.compilerThread.0.compiles=8
sun.ci.compilerThread.0.method=""
sun.ci.compilerThread.0.time=4
sun.ci.compilerThread.0.type=1
sun.ci.compilerThread.1.compiles=4
sun.ci.compilerThread.1.method=""
sun.ci.compilerThread.1.time=3
sun.ci.compilerThread.1.type=1
sun.ci.compilerThread.2.compiles=97
sun.ci.compilerThread.2.method=""
sun.ci.compilerThread.2.time=10
sun.ci.compilerThread.2.type=1
sun.ci.lastFailedMethod=""
sun.ci.lastFailedType=0
sun.ci.lastInvalidatedMethod=""
sun.ci.lastInvalidatedType=0
sun.ci.lastMethod="sun/misc/ASCIICaseInsensitiveComparator compare"
sun.ci.lastSize=264
sun.ci.lastType=1
sun.ci.nmethodCodeSize=100000
sun.ci.nmethodSize=167824
sun.ci.osrBytes=0
sun.ci.osrCompiles=0
sun.ci.osrTime=0
sun.ci.standardBytes=7514
sun.ci.standardCompiles=109
sun.ci.standardTime=106668
sun.ci.threads=3
sun.ci.totalBailouts=0
sun.ci.totalCompiles=109
sun.ci.totalInvalidates=0
sun.classloader.findClassTime=24540700
sun.classloader.findClasses=46
sun.classloader.parentDelegationTime=3007529
sun.cls.appClassBytes=137124
sun.cls.appClassLoadCount=106
sun.cls.appClassLoadTime=53848
sun.cls.appClassLoadTime.self=24776
sun.cls.classInitTime=124090
sun.cls.classInitTime.self=77927
sun.cls.classLinkedTime=74692
sun.cls.classLinkedTime.self=28333
sun.cls.classVerifyTime=46283
sun.cls.classVerifyTime.self=15996
sun.cls.defineAppClassTime=19317
sun.cls.defineAppClassTime.self=760
sun.cls.defineAppClasses=46
sun.cls.initializedClasses=500
sun.cls.isUnsyncloadClassSet=0
sun.cls.jniDefineClassNoLockCalls=0
sun.cls.jvmDefineClassNoLockCalls=46
sun.cls.jvmFindLoadedClassNoLockCalls=212
sun.cls.linkedClasses=588
sun.cls.loadInstanceClassFailRate=0
sun.cls.loadedBytes=1298848
sun.cls.lookupSysClassTime=26691
sun.cls.methodBytes=830360
sun.cls.nonSystemLoaderLockContentionRate=0
sun.cls.parseClassTime=90729
sun.cls.parseClassTime.self=77100
sun.cls.sharedClassLoadTime=25
sun.cls.sharedLoadedBytes=0
sun.cls.sharedUnloadedBytes=0
sun.cls.sysClassBytes=2114821
sun.cls.sysClassLoadTime=122868
sun.cls.systemLoaderLockContentionRate=0
sun.cls.time=265053
sun.cls.unloadedBytes=0
sun.cls.unsafeDefineClassCalls=0
sun.cls.verifiedClasses=559
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=706740224
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=705691648
sun.gc.generation.0.space.0.name="eden"
sun.gc.generation.0.space.0.used=6151536
sun.gc.generation.0.space.1.capacity=5242880
sun.gc.generation.0.space.1.initCapacity=0
sun.gc.generation.0.space.1.maxCapacity=235405312
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=235405312
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=1413480448
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=1413480448
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=764080
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=3117841
sun.os.hrt.ticks=112459180
sun.perfdata.majorVersion=2
sun.perfdata.minorVersion=0
sun.perfdata.overflow=0
sun.perfdata.size=65536
sun.perfdata.timestamp=201939
sun.perfdata.used=17616
sun.property.sun.boot.class.path="F:\soft\Java\jre1.8\lib\resources.jar;F:\soft\Java\jre1.8\lib\rt.jar;F:\soft\Java\jre1.8\lib\sunrsasign.jar;F:\soft\Java\jre1.8\lib\jsse.jar;F:\soft\Java\jre1.8\lib\jce.jar;F:\soft\Java\jre1.8\lib\charsets.jar;F:\soft\Java\jre1.8\lib\jfr.jar;F:\soft\Java\jre1.8\classes"
sun.property.sun.boot.library.path="F:\soft\Java\jre1.8\bin"
sun.rt._sync_ContendedLockAttempts=12
sun.rt._sync_Deflations=46
sun.rt._sync_EmptyNotifications=0
sun.rt._sync_FailedSpins=0
sun.rt._sync_FutileWakeups=2
sun.rt._sync_Inflations=50
sun.rt._sync_MonExtant=384
sun.rt._sync_MonInCirculation=0
sun.rt._sync_MonScavenged=0
sun.rt._sync_Notifications=25
sun.rt._sync_Parks=32
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=12630762
sun.rt.createVmBeginTime=1505290045108
sun.rt.createVmEndTime=1505290045168
sun.rt.internalVersion="Java HotSpot(TM) 64-Bit Server VM (25.101-b13) for windows-amd64 JRE (1.8.0_101-b13), built on Jun 22 2016 01:21:29 by "java_re" with MS VC++ 10.0 (VS2010)"
sun.rt.interruptedBeforeIO=0
sun.rt.interruptedDuringIO=0
sun.rt.javaCommand="boss-1.0.1.jar 2 127.0.0.1 80"
sun.rt.jvmCapabilities="1100000000000000000000000000000000000000000000000000000000000000"
sun.rt.jvmVersion=426049549
sun.rt.safepointSyncTime=238
sun.rt.safepointTime=761
sun.rt.safepoints=3
sun.rt.threadInterruptSignaled=0
sun.rt.vmInitDoneTime=1505290045155
sun.threads.vmOperationTime=184
sun.urlClassLoader.readClassBytesTime=6458313
sun.zip.zipFile.openTime=3587098
sun.zip.zipFiles=2

诊断命令

诊断命令的帮助信息

D:\>jcmd 9816 help
9816:
The following commands are available:
JFR.stop
JFR.start
JFR.dump
JFR.check
VM.native_memory
VM.check_commercial_features
VM.unlock_commercial_features
ManagementAgent.stop
ManagementAgent.start_local
ManagementAgent.start
GC.rotate_log
Thread.print
GC.class_stats
GC.class_histogram
GC.heap_dump
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 '.

其中9816是某个jvm进程的pid。

具体诊断命令的帮助

如下是GC.run诊断命令的帮助信息。

D:\>jcmd 9816 help GC.run
9816:
GC.run
Call java.lang.System.gc().

Impact: Medium: Depends on Java heap size and content.

Syntax: GC.run

诊断命令的应用

GC.run诊断命令

诊断前：

D:\>jstat -gcutil 9816 500 7
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000
  0.00   0.00  24.05   0.00  16.66  19.75      0    0.000     0    0.000    0.000

进行诊断操作：

D:\>jcmd 9816 GC.run
9816:
Command executed successfully

诊断后：

D:\>jstat -gcutil 9816 500 7
  S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006
  0.00   0.00   0.00   1.21  79.67  87.24      1    0.001     1    0.004    0.006

在诊断前后，请注意FGC(Full GC)的变化。

VM.flags诊断命令

此命令只是显示JVM的参数信息。

D:\>jcmd 9816 VM.flags
9816:
-XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2120220672 -XX:MaxNewSize=706740224 -XX:MinHeapDelta
Bytes=524288 -XX:NewSize=44564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseFa
stUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

还有更多有用的诊断命令，请自己查验。

## jinfo-查看系统信息和JVM信息
### 帮助信息
主要的参数是-flags打印JVM的信息和-sysprops打印系统的信息。

F:\soft\Java\jdk1.8\bin>jinfo
Usage:
jinfo [option]
(to connect to running process)
jinfo [option]

### 使用实例

F:\soft\Java\jdk1.8\bin>jinfo 5952
Attaching to process ID 5952, please wait…
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13
Java System Properties:

java.runtime.name = Java(TM) SE Runtime Environment
java.vm.version = 25.101-b13
sun.boot.library.path = F:\soft\Java\jre1.8\bin
java.vendor.url = http://java.oracle.com/
java.vm.vendor = Oracle Corporation
path.separator = ;
file.encoding.pkg = sun.io
java.vm.name = Java HotSpot(TM) 64-Bit Server VM
sun.os.patch.level = Service Pack 1
sun.java.launcher = SUN_STANDARD
user.script =
user.country = CN
user.dir = D:\web_work\boss\target
java.vm.specification.name = Java Virtual Machine Specification
java.runtime.version = 1.8.0_101-b13
java.awt.graphicsenv = sun.awt.Win32GraphicsEnvironment
os.arch = amd64
java.endorsed.dirs = F:\soft\Java\jre1.8\lib\endorsed
line.separator =

java.io.tmpdir = C:\Users\MICHAE~1\AppData\Local\Temp\
java.vm.specification.vendor = Oracle Corporation
user.variant =
os.name = Windows 7
sun.jnu.encoding = GBK
java.library.path = C:\ProgramData\Oracle\Java\javapath;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:\Progra
mData\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell
\v1.0\;D:\soft\svn\bin;F:\soft\Java\jdk1.8\bin;E:\DTool\sdk\platform-tools;E:\DTool\sdk\tools;%MAVEN_HOME%\bin;D:\apache
-maven-3.3.9\bin;D:\soft\MySQL\MySQLServer\bin;D:\as\gradle\gradle-2.14.1\bin;H:\php56\;H:\php56\ext;H:\DownLoad\apache-
ant-1.10.1\bin;F:\Program Files\Git\cmd;F:\Program Files\Git\mingw64\bin;F:\Program Files\Git\usr\bin;F:\Program Files\V
isualSVN Server\bin;F:\soft\python3;F:\Program Files (x86)\AllWinnerTech\PhoenixSuit\;.
java.specification.name = Java Platform API Specification
java.class.version = 52.0
sun.management.compiler = HotSpot 64-Bit Tiered Compilers
os.version = 6.1
user.home = C:\Users\MichaelKoo
user.timezone =
java.awt.printerjob = sun.awt.windows.WPrinterJob
file.encoding = GBK
java.specification.version = 1.8
user.name = MichaelKoo
java.class.path = boss-1.0.1.jar
java.vm.specification.version = 1.8
sun.arch.data.model = 64
sun.java.command = boss-1.0.1.jar 2 124.42.243.67 8010
java.home = F:\soft\Java\jre1.8
user.language = zh
java.specification.vendor = Oracle Corporation
awt.toolkit = sun.awt.windows.WToolkit
java.vm.info = mixed mode
java.version = 1.8.0_101
java.ext.dirs = F:\soft\Java\jre1.8\lib\ext;C:\Windows\Sun\Java\lib\ext
sun.boot.class.path = F:\soft\Java\jre1.8\lib\resources.jar;F:\soft\Java\jre1.8\lib\rt.jar;F:\soft\Java\jre1.8\lib\sunrs
asign.jar;F:\soft\Java\jre1.8\lib\jsse.jar;F:\soft\Java\jre1.8\lib\jce.jar;F:\soft\Java\jre1.8\lib\charsets.jar;F:\soft\
Java\jre1.8\lib\jfr.jar;F:\soft\Java\jre1.8\classes
java.vendor = Oracle Corporation
sun.stderr.encoding = ms936
file.separator = \
java.vendor.url.bug = http://bugreport.sun.com/bugreport/
sun.io.unicode.encoding = UnicodeLittle
sun.cpu.endian = little
sun.stdout.encoding = ms936
sun.desktop = windows
sun.cpu.isalist = amd64

VM Flags:
Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2120220672 -XX:MaxNewSize=7067
40224 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCom
pressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
Command line:

### 使用实例2-显示jvm参数

F:\soft\Java\jdk1.8\bin>jinfo -flags 5952
Attaching to process ID 5952, please wait…
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13
Non-default VM flags: -XX:CICompilerCount=3 -XX:InitialHeapSize=134217728 -XX:MaxHeapSize=2120220672 -XX:MaxNewSize=7067
40224 -XX:MinHeapDeltaBytes=524288 -XX:NewSize=44564480 -XX:OldSize=89653248 -XX:+UseCompressedClassPointers -XX:+UseCom
pressedOops -XX:+UseFastUnorderedTimeStamps -XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC
Command line:

## jmap-查看堆信息
### 帮助信息
经常用到的参数有-heap显示堆信息和-clstats显示ClassLoader信息。

F:\soft\Java\jdk1.8\bin>jmap
Usage:
jmap [option]
(to connect to running process)
jmap [option]

### 使用实例
#### 查看堆信息

F:\soft\Java\jdk1.8\bin>jmap.exe -heap 5952
Attaching to process ID 5952, please wait…
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
MinHeapFreeRatio = 0
MaxHeapFreeRatio = 100
MaxHeapSize = 2120220672 (2022.0MB)
NewSize = 44564480 (42.5MB)
MaxNewSize = 706740224 (674.0MB)
OldSize = 89653248 (85.5MB)
NewRatio = 2
SurvivorRatio = 8
MetaspaceSize = 21807104 (20.796875MB)
CompressedClassSpaceSize = 1073741824 (1024.0MB)
MaxMetaspaceSize = 17592186044415 MB
G1HeapRegionSize = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
capacity = 34078720 (32.5MB)
used = 7515688 (7.167518615722656MB)
free = 26563032 (25.332481384277344MB)
22.05390343299279% used
From Space:
capacity = 5242880 (5.0MB)
used = 0 (0.0MB)
free = 5242880 (5.0MB)
0.0% used
To Space:
capacity = 5242880 (5.0MB)
used = 0 (0.0MB)
free = 5242880 (5.0MB)
0.0% used
PS Old Generation
capacity = 89653248 (85.5MB)
used = 0 (0.0MB)
free = 89653248 (85.5MB)
0.0% used

2086 interned Strings occupying 186928 bytes.

#### 查看堆中的对象(以下是查看java.net包下的所有对象)

F:\soft\Java\jdk1.8\bin>jmap.exe -histo 5952 |findstr java.net.*
26: 26 1664 java.net.URL
83: 2 176 java.net.DualStackPlainSocketImpl
84: 2 176 java.net.PlainSocketImpl
90: 2 160 java.net.URI
106: 2 96 java.net.SocketInputStream
107: 2 96 java.net.SocketOutputStream
127: 3 72 java.net.Proxy Type138:264java.net.InetAddress InetAddressHolder
139: 2 64 java.net.Socket
151: 2 48 java.net.Inet4Address
152: 2 48 java.net.InetAddress Cache153:248java.net.InetAddress Cache Type177:132[Ljava.net.Proxy Type;
200: 1 24 [Ljava.net.InetAddress Cache Type;
209: 1 24 java.net.Inet6AddressImpl
210: 1 24 java.net.Proxy
248: 1 16 java.net.InetAddress 2249:116java.net.URLClassLoader 7

### 查看所有classloader

F:\soft\Java\jdk1.8\bin>jmap -clstats 5952
Attaching to process ID 5952, please wait…
Debugger attached successfully.
Server compiler detected.
JVM version is 25.101-b13
finding class loader instances ..done.
computing per loader stat ..done.
please wait.. computing liveness…liveness analysis may be inaccurate …
class_loader classes bytes parent_loader alive? type

1547 2700258 null live
0x0000000081b010b0 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b016f0 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01d30 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02370 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b029b0 1 892 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b03b30 2 4839 null dead javax/management/remote/rmi/NoCallStackClassLoader@0x000
0000016e037e0
0x0000000081b01178 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b017b8 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01df8 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02438 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02a78 1 892 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b007a0 12 36867 0x0000000081a02f58 dead sun/reflect/misc/MethodUtil@0x0000000016e46e78
0x0000000081b00f20 1 1485 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01560 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01ba0 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b021e0 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02820 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081a02fb8 0 0 null live sun/misc/Launcher ExtClassLoader@0x0000000016d3fa300x0000000081b00fe811474nulldeadsun/reflect/DelegatingClassLoader@0x0000000016d39df80x0000000081b0162811474nulldeadsun/reflect/DelegatingClassLoader@0x0000000016d39df80x0000000081b01c681880nulldeadsun/reflect/DelegatingClassLoader@0x0000000016d39df80x0000000081b022a81880nulldeadsun/reflect/DelegatingClassLoader@0x0000000016d39df80x0000000081b028e811474nulldeadsun/reflect/DelegatingClassLoader@0x0000000016d39df80x0000000081b92ba0000x0000000081a02f58deadjava/util/ResourceBundle RBClassLoader@0x0000000
016dac448
0x0000000081b013d0 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01a10 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02050 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02690 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02cd0 1 889 0x0000000081b007a0 dead sun/reflect/DelegatingClassLoader@0x0000000016d3
9df8
0x0000000081b01498 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01ad8 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02118 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02758 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02d98 1 882 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01240 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01880 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01ec0 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02500 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02b40 1 892 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081a02f58 119 249212 0x0000000081a02fb8 live sun/misc/Launcher$AppClassLoader@0x0000000016d3f
688
0x0000000081b01308 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01948 1 892 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b01f88 1 880 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b025c8 1 1474 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b02c08 1 1475 null dead sun/reflect/DelegatingClassLoader@0x0000000016d39df8
0x0000000081b03c08 4 4012 null dead javax/management/remote/rmi/NoCallStackClassLoader@0x000
0000016e037e0

total = 47 1724 3043527 N/A alive=3, dead=44 N/A

## jstack-打印堆栈相关信息
此命令可以详细打印出来堆栈信息
### 帮助信息
```F:\soft\Java\jdk1.8\bin>jstack.exe
Usage:
    jstack [-l] 
        (to connect to running process)
    jstack -F [-m] [-l] 
        (to connect to a hung process)
    jstack [-m] [-l]  
        (to connect to a core file)
    jstack [-m] [-l] [server_id@]or hostname>
        (to connect to a remote debug server)

Options:
    -F  to force a thread dump. Use when jstack  does not respond (process is hung)
    -m  to print both java and native frames (mixed mode)
    -l  long listing. Prints additional information about locks
    -h or -help to print this help message




<div class="se-preview-section-delimiter">div>

使用实例

F:\soft\Java\jdk1.8\bin>jstack.exe 5952
2017-09-12 16:03:53
Full thread dump Java HotSpot(TM) 64-Bit Server VM (25.101-b13 mixed mode):

"RMI Scheduler(0)" #20 daemon prio=5 os_prio=0 tid=0x000000005a84a800 nid=0xd54 waiting on condition [0x000000005afcf000
]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x00000000d63564c0> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionOb
ject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$DelayedWorkQueue.take(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

"RMI TCP Accept-0" #18 daemon prio=5 os_prio=0 tid=0x0000000058e04000 nid=0x1304 runnable [0x0000000059e4e000]
   java.lang.Thread.State: RUNNABLE
        at java.net.DualStackPlainSocketImpl.accept0(Native Method)
        at java.net.DualStackPlainSocketImpl.socketAccept(Unknown Source)
        at java.net.AbstractPlainSocketImpl.accept(Unknown Source)
        at java.net.PlainSocketImpl.accept(Unknown Source)
        - locked <0x00000000d6358348> (a java.net.SocksSocketImpl)
        at java.net.ServerSocket.implAccept(Unknown Source)
        at java.net.ServerSocket.accept(Unknown Source)
        at sun.management.jmxremote.LocalRMIServerSocketFactory$1.accept(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.executeAcceptLoop(Unknown Source)
        at sun.rmi.transport.tcp.TCPTransport$AcceptLoop.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

"Timer-1" #16 prio=5 os_prio=0 tid=0x0000000058cac000 nid=0x16bc in Object.wait() [0x000000005a11f000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000081a012b0> (a java.util.TaskQueue)
        at java.util.TimerThread.mainLoop(Unknown Source)
        - locked <0x0000000081a012b0> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Unknown Source)

"Timer-0" #15 prio=5 os_prio=0 tid=0x0000000058cab000 nid=0x4f0 in Object.wait() [0x0000000059fdf000]
   java.lang.Thread.State: TIMED_WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000081a01480> (a java.util.TaskQueue)
        at java.util.TimerThread.mainLoop(Unknown Source)
        - locked <0x0000000081a01480> (a java.util.TaskQueue)
        at java.util.TimerThread.run(Unknown Source)

"WebsocketWriteThread" #14 prio=5 os_prio=0 tid=0x0000000058bb3800 nid=0x1020 waiting on condition [0x0000000059d1f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000081a01658> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionOb
ject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.java_websocket.client.WebSocketClient$WebsocketWriteThread.run(WebSocketClient.java:413)
        at java.lang.Thread.run(Unknown Source)

"WebsocketWriteThread" #13 prio=5 os_prio=0 tid=0x0000000058bb3000 nid=0x1324 waiting on condition [0x0000000059aee000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x0000000081a02578> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionOb
ject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at org.java_websocket.client.WebSocketClient$WebsocketWriteThread.run(WebSocketClient.java:413)
        at java.lang.Thread.run(Unknown Source)

"DestroyJavaVM" #12 prio=5 os_prio=0 tid=0x000000000259e000 nid=0x1040 waiting on condition [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Thread-1" #11 prio=5 os_prio=0 tid=0x0000000058ba2000 nid=0xcd8 runnable [0x0000000059bfe000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.socketRead(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at org.java_websocket.client.WebSocketClient.run(WebSocketClient.java:228)
        at java.lang.Thread.run(Unknown Source)

"Thread-0" #10 prio=5 os_prio=0 tid=0x0000000058ba1800 nid=0x1614 runnable [0x00000000597de000]
   java.lang.Thread.State: RUNNABLE
        at java.net.SocketInputStream.socketRead0(Native Method)
        at java.net.SocketInputStream.socketRead(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at java.net.SocketInputStream.read(Unknown Source)
        at org.java_websocket.client.WebSocketClient.run(WebSocketClient.java:228)
        at java.lang.Thread.run(Unknown Source)

"Service Thread" #9 daemon prio=9 os_prio=0 tid=0x0000000058afe800 nid=0x1158 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"C1 CompilerThread2" #8 daemon prio=9 os_prio=2 tid=0x0000000058a7b000 nid=0x1054 waiting on condition [0x00000000000000
00]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread1" #7 daemon prio=9 os_prio=2 tid=0x0000000058a79800 nid=0x16d8 waiting on condition [0x00000000000000
00]
   java.lang.Thread.State: RUNNABLE

"C2 CompilerThread0" #6 daemon prio=9 os_prio=2 tid=0x000000005772f000 nid=0x1708 waiting on condition [0x00000000000000
00]
   java.lang.Thread.State: RUNNABLE

"Attach Listener" #5 daemon prio=5 os_prio=2 tid=0x0000000057721000 nid=0x132c waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

"Signal Dispatcher" #4 daemon prio=9 os_prio=2 tid=0x0000000058a73000 nid=0xd7c runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE

"Finalizer" #3 daemon prio=8 os_prio=1 tid=0x0000000057709000 nid=0x12f8 in Object.wait() [0x0000000058a5f000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000081a1d208> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(Unknown Source)
        - locked <0x0000000081a1d208> (a java.lang.ref.ReferenceQueue$Lock)
        at java.lang.ref.ReferenceQueue.remove(Unknown Source)
        at java.lang.ref.Finalizer$FinalizerThread.run(Unknown Source)

"Reference Handler" #2 daemon prio=10 os_prio=2 tid=0x00000000576c2000 nid=0x1714 in Object.wait() [0x000000005879e000]
   java.lang.Thread.State: WAITING (on object monitor)
        at java.lang.Object.wait(Native Method)
        - waiting on <0x0000000081a16218> (a java.lang.ref.Reference$Lock)
        at java.lang.Object.wait(Unknown Source)
        at java.lang.ref.Reference.tryHandlePending(Unknown Source)
        - locked <0x0000000081a16218> (a java.lang.ref.Reference$Lock)
        at java.lang.ref.Reference$ReferenceHandler.run(Unknown Source)

"VM Thread" os_prio=2 tid=0x00000000576ba000 nid=0xb54 runnable

"GC task thread#0 (ParallelGC)" os_prio=0 tid=0x000000000247c000 nid=0x1640 runnable

"GC task thread#1 (ParallelGC)" os_prio=0 tid=0x000000000247d800 nid=0xa44 runnable

"GC task thread#2 (ParallelGC)" os_prio=0 tid=0x000000000247f000 nid=0x680 runnable

"GC task thread#3 (ParallelGC)" os_prio=0 tid=0x0000000002481000 nid=0x1630 runnable

"VM Periodic Task Thread" os_prio=2 tid=0x0000000058b37800 nid=0x278 waiting on condition

JNI global references: 359