? jmap命令是一個可以輸出所有內(nèi)存中對象的工具，甚至可以將VM 中的heap，以二進制輸出成文本。打印出某個java進程（使用pid）內(nèi)存內(nèi)的，所有‘對象’的情況（如：產(chǎn)生那些對象摊灭，及其數(shù)量）。
語法
C:\Users\shuqi>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
-clstats to print class loader 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
生成dump文件
C:\Users\shuqi>jmap -dump:live,format=b,file=d:\\d.bin 9880
Dumping heap to D:\d.bin ...
Heap dump file created
打印Heap信息
C:\Users\shuqi>jmap -heap 9880
Attaching to process ID 9880, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14
using thread-local object allocation.
Parallel GC with 8 thread(s)
Heap Configuration:
MinHeapFreeRatio = 0
MaxHeapFreeRatio = 100
MaxHeapSize = 1073741824 (1024.0MB)
NewSize = 44564480 (42.5MB)
MaxNewSize = 357564416 (341.0MB)
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 = 26214400 (25.0MB)
used = 1048720 (1.0001373291015625MB)
free = 25165680 (23.999862670898438MB)
4.00054931640625% used
From Space:
capacity = 524288 (0.5MB)
used = 294912 (0.28125MB)
free = 229376 (0.21875MB)
56.25% used
To Space:
capacity = 524288 (0.5MB)
used = 0 (0.0MB)
free = 524288 (0.5MB)
0.0% used
PS Old Generation
capacity = 54001664 (51.5MB)
used = 13028944 (12.425369262695312MB)
free = 40972720 (39.07463073730469MB)
24.126930607175364% used
11332 interned Strings occupying 1040832 bytes.
