jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
     //option                   //vmid  //查询间隔    //查询次数 
 
 -t参数可以在输出信息前加一个timestamp列，显示程序的运行时间
 -h参数可以在周期性数据输出时，输出多少行数据后，跟着输出一个表头信息。
 
 -interval参数用于指定统计数据的输出周期，单位是毫秒
 -count参数用于指定输出的次数

[~]$ jstat -help
Usage: jstat -help|-options
       jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

Definitions:
  <option>      An option reported by the -options option
  <vmid>        Virtual Machine Identifier. A vmid takes the following form:
                     <lvmid>[@<hostname>[:<port>]]
                Where <lvmid> is the local vm identifier for the target
                Java virtual machine, typically a process id; <hostname> is
                the name of the host running the target Java virtual machine;
                and <port> is the port number for the rmiregistry on the
                target host. See the jvmstat documentation for a more complete
                description of the Virtual Machine Identifier.
  <lines>       Number of samples between header lines.
  <interval>    Sampling interval. The following forms are allowed:
                    <n>["ms"|"s"]
                Where <n> is an integer and the suffix specifies the units as 
                milliseconds("ms") or seconds("s"). The default units are "ms".
  <count>       Number of samples to take before terminating.
  -J<flag>      Pass <flag> directly to the runtime system.

-class             //监视类装载、卸载数量、总空间以及类装载所耗费的时间  
  
-gc                //监视JAVA堆状况，包括Eden区、两个Survivor区、老年代、永久代等的容量、已用空间、GC时间合计等信息  
-gccapacity        //监视内容与-gc基本相同，但输出主要关注java堆各个区域使用到的最大、最小空间
-gcutil            //监视内容与-gc基本相同，但输出主要关注已使用空间占总空间的百分比
-gccause           //与-gcutil功能一样，但是会额外输出导致上一次GC产生的原因

-gcnew             //监视新生代的GC状况
-gcnewcapacity     //监视内容与-gcnew基本相同，输出主要关注使用到的最大、最小空间
  
-gcold             //监视老年代的GC状况
-gcoldcapacity     //监视内容与-gcold基本相同，输出主要关注使用到的最大、最小空间

-gcpermcapacity  //输出永久代使用到的最大、最小空间

-compiler          //输出JIT编译器编译过的方法、耗时等信息
-printcompilation  //输出已经被JIT编译的方法

[sankuai@set-xr-cx-etcp-code-test02 ~]$ jmap
Usage:
    jmap [option] <pid>
        (to connect to running process)
    jmap [option] <executable <core>
        (to connect to a core file)
    jmap [option] [server_id@]<remote server IP or hostname>
        (to connect to remote debug server)

where <option> is one of:
    <none>               to print same info as Solaris pmap
    -heap                to print java heap summary
    -histo[:live]        to print histogram of java object heap; if the "live"
                         suboption is specified, only count live objects
    -permstat            to print permanent generation statistics
    -finalizerinfo       to print information on objects awaiting finalization
    -dump:<dump-options> to dump java heap in hprof binary format
                         dump-options:
                           live         dump only live objects; if not specified,
                                        all objects in the heap are dumped.
                           format=b     binary format
                           file=<file>  dump heap to <file>
                         Example: jmap -dump:live,format=b,file=heap.bin <pid>
    -F                   force. Use with -dump:<dump-options> <pid> or -histo
                         to force a heap dump or histogram when <pid> does not
                         respond. The "live" suboption is not supported
                         in this mode.
    -h | -help           to print this help message
    -J<flag>             to pass <flag> directly to the runtime system

jmap -heap pid

[~]$ ./jmap -heap 192610
Attaching to process ID 192610, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.45-b02

using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC

Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 4294967296 (4096.0MB)
   NewSize                  = 1073741824 (1024.0MB)
   MaxNewSize               = 1073741824 (1024.0MB)
   OldSize                  = 3221225472 (3072.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 268435456 (256.0MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 268435456 (256.0MB)
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
New Generation (Eden + 1 Survivor Space):	
   capacity = 966393856 (921.625MB)
   used     = 641636608 (611.912353515625MB)
   free     = 324757248 (309.712646484375MB)
   66.39493866980877% used
Eden Space:
   capacity = 859045888 (819.25MB)
   used     = 637358448 (607.8323822021484MB)
   free     = 221687440 (211.41761779785156MB)
   74.19376041527597% used
From Space:
   capacity = 107347968 (102.375MB)
   used     = 4278160 (4.0799713134765625MB)
   free     = 103069808 (98.29502868652344MB)
   3.9853199643238706% used
To Space:
   capacity = 107347968 (102.375MB)
   used     = 0 (0.0MB)
   free     = 107347968 (102.375MB)
   0.0% used
concurrent mark-sweep generation:
   capacity = 3221225472 (3072.0MB)
   used     = 230203712 (219.53936767578125MB)
   free     = 2991021760 (2852.4606323242188MB)
   7.146463791529338% used

40359 interned Strings occupying 4225896 bytes.

[sankuai@set-xr-cx-etcp-code-test02 bin]$ jmap -histo:live 192610|more

 num     #instances         #bytes  class name
----------------------------------------------
   1:         46961      131287216  [B
   2:         97908       11794768  [C
   3:         97796        3129472  java.util.HashMap$Node
   4:         96182        2308368  java.lang.String
   5:         40884        1962432  java.util.zip.Inflater
   6:         19559        1721192  java.lang.reflect.Method
   7:         41890        1675600  java.lang.ref.Finalizer
   8:         13968        1601808  java.lang.Class
   9:         40355        1291360  java.util.concurrent.ConcurrentHashMap$Node
  10:         18310        1216328  [Ljava.lang.Object;
  11:          8753        1120216  [Ljava.util.HashMap$Node;
  12:         25015        1000600  java.util.WeakHashMap$Entry
  13:         40884         981216  java.util.zip.ZStreamRef
  14:         35328         847872  io.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry
  15:         16585         796080  org.aspectj.weaver.reflect.ShadowMatchImpl
  16:         15397         684208  [Z
  17:         16585         530720  org.aspectj.weaver.patterns.ExposedState
  18:           965         500552  [Ljava.util.concurrent.ConcurrentHashMap$Node;
  19:           582         469072  [Ljava.util.WeakHashMap$Entry;
  20:         10759         430360  java.util.LinkedHashMap$Entry
  21:          6367         425216  [I
  22:         11721         375072  java.lang.ref.WeakReference
  23:          6664         373184  java.util.LinkedHashMap
  24:         10486         335552  java.util.Hashtable$Entry
  25:          6118         293664  java.util.HashMap
  26:         18146         290336  java.lang.Integer
  27:          9961         239056  [Lorg.aspectj.weaver.ast.Var;
  28:          9721         233304  java.lang.Long
  29:          9096         218304  java.util.ArrayList
  30:          5303         212120  java.util.TreeMap$Entry
  31:          5158         206320  java.lang.ref.SoftReference
  32:          8806         191152  [Ljava.lang.Class;
  33:          3742         174048  [Ljava.lang.String;
  34:          5170         165440  org.jacoco.agent.rt.internal_b0d6a23.core.data.ExecutionData
  35:            80         142592  [Lio.netty.buffer.PoolThreadCache$MemoryRegionCache$Entry;
  36:          2073         132672  java.util.concurrent.ConcurrentHashMap
  37:          5514         132336  java.beans.MethodRef
  38:          1634         130720  java.lang.reflect.Constructor
  39:           411         119296  [Ljava.util.Hashtable$Entry;
  40:          6966         111456  java.lang.Object
  41:           293         110168  java.lang.Thread
  42:          1069         102624  org.springframework.beans.GenericTypeAwarePropertyDescriptor
  43:          3984          95616  java.util.concurrent.atomic.AtomicLong
  44:            62          91416  [Ljava.nio.ByteBuffer;
  45:          3712          89088  org.springframework.core.MethodClassKey
  46:          3661          87864  sun.reflect.generics.tree.SimpleClassTypeSignature
  47:          1500          84000  java.beans.MethodDescriptor
  48:          1162          83664  java.lang.reflect.Field
  49:          2447          78304  java.util.LinkedList
  50:          3132          75168  java.util.jar.Attributes$Name
  51:          2924          70176  java.util.LinkedList$Node

class name表示对象类型
B  byte
C  char
D  double
F  float
I  int
J  long
Z  boolean
[  数组，如[I表示int[]
[L+类名 其他对象