查看JVM各个代的内存状态

//在Linux执行 jmap -heap [pid] 
//可以看到如下信息
Attaching to process ID 23990, please wait...
Warning: the type "const char*" (declared in the remote VM in VMStructs::localHotSpotVMTypes) had its size declared as 8 twice. Continuing.
Warning: the type "const size_t" (declared in the remote VM in VMStructs::localHotSpotVMTypes) had its size declared as 8 twice. Continuing.
Warning: the type "const int" (declared in the remote VM in VMStructs::localHotSpotVMTypes) had its size declared as 4 twice. Continuing.
Warning: the type "const MemRegion" (declared in the remote VM in VMStructs::localHotSpotVMTypes) had its size declared as 16 twice. Continuing.
Debugger attached successfully.
Server compiler detected.
JVM version is 21.0-b17
using parallel threads in the new generation.
using thread-local object allocation.
Concurrent Mark-Sweep GC
Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 5368709120 (5120.0MB)
   NewSize          = 1073741824 (1024.0MB)
   MaxNewSize       = 1073741824 (1024.0MB)
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 536870912 (512.0MB)
   MaxPermSize      = 536870912 (512.0MB)
Heap Usage:
New Generation (Eden + 1 Survivor Space):
   capacity = 966393856 (921.625MB)
   used     = 282829160 (269.7269058227539MB)
   free     = 683564696 (651.8980941772461MB)
   29.266448482056575% used
Eden Space:
   capacity = 859045888 (819.25MB)
   used     = 203344848 (193.9247589111328MB)
   free     = 655701040 (625.3252410888672MB)
   23.671011157904523% used
From Space:
   capacity = 107347968 (102.375MB)
   used     = 79484312 (75.8021469116211MB)
   free     = 27863656 (26.572853088378906MB)
   74.04361114688263% used
To Space:
   capacity = 107347968 (102.375MB)
   used     = 0 (0.0MB)
   free     = 107347968 (102.375MB)
   0.0% used
concurrent mark-sweep generation:
   capacity = 4294967296 (4096.0MB)
   used     = 46904664 (44.731773376464844MB)
   free     = 4248062632 (4051.268226623535MB)
   1.0920843109488487% used
Perm Generation:
   capacity = 536870912 (512.0MB)
   used     = 81989448 (78.19123077392578MB)
   free     = 454881464 (433.8087692260742MB)
   15.27172476053238% used
 
导出整个JVM的内存
jmap -dump:format=b,file=memory.log [pid]
 
使用JHat分析JVM堆dump文件的工具，基于此工具可以分析JVM heap中对象占用状况
jhat -J-Xmx1024M [file] 
执行后等待console中输出Started HTTP server on port 7000
然后就可以使用浏览器访问HTTP：//ip:7000