jvm信息jmap使用的基本方法教程

[root@bogon /]# jmap -help
Usage:
 jmap [option] 
  (to connect to running process)
 jmap [option] 
  (to connect to a core file)
 jmap [option] [server_id@]
  (to connect to remote debug server)

where  is one of:
     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: 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= dump heap to 
       Example: jmap -dump:live,format=b,file=heap.bin 
 -F     force. Use with -dump:  or -histo
       to force a heap dump or histogram when  does not
       respond. The "live" suboption is not supported
       in this mode.
 -h | -help   to print this help message
 -J    to pass  directly to the runtime system

[root@bogon /]# jmap 922
Attaching to process ID 922, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14
0x0000000000400000 7K /usr/local/software/java/bin/java
0x0000003ddde00000 153K /lib64/ld-2.12.so
0x0000003dde200000 22K /lib64/libdl-2.12.so
0x0000003dde600000 1881K /lib64/libc-2.12.so
0x0000003ddea00000 142K /lib64/libpthread-2.12.so
0x0000003ddee00000 45K /lib64/librt-2.12.so
0x0000003ddf200000 585K /lib64/libm-2.12.so
0x0000003de0e00000 111K /lib64/libresolv-2.12.so
0x0000003de9e00000 91K /lib64/libgcc_s-4.4.7-20120601.so.1
0x00007f90de586000 26K /lib64/libnss_DNS-2.12.so
0x00007f913c39d000 250K /usr/local/software/java/jre/lib/amd64/libsunec.so
0x00007f913cbf2000 90K /usr/local/software/java/jre/lib/amd64/libnio.so
0x00007f913d103000 113K /usr/local/software/java/jre/lib/amd64/libnet.so
0x00007f913d31a000 49K /usr/local/software/java/jre/lib/amd64/libmanagement.so
0x00007f919a43b000 121K /usr/local/software/java/jre/lib/amd64/libzip.so
0x00007f919a656000 64K /lib64/libnss_files-2.12.so
0x00007f919a874000 220K /usr/local/software/java/jre/lib/amd64/libjava.so
0x00007f919aaa0000 64K /usr/local/software/java/jre/lib/amd64/libverify.so
0x00007f919acef000 16584K /usr/local/software/java/jre/lib/amd64/server/libjvm.so
0x00007f919bce2000 100K /usr/local/software/java/lib/amd64/jli/libjli.so

[root@bogon /]# jmap -heap 922
Attaching to process ID 922, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14

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) 最大堆大小
 NewSize     = 3221225472 (3072.0MB) 新生代大小
 MaxNewSize    = 3221225472 (3072.0MB) 最大分配新生代内存
 OldSize     = 1073741824 (1024.0MB) 老年代大小
 NewRatio     = 2 
 SurvivorRatio   = 8 新生代与老年代的比例
 MetaspaceSize   = 21807104 (20.796875MB) 
 CompressedClassSpaceSize = 1073741824 (1024.0MB)
 MaxMetaspaceSize   = 17592186044415 MB
 G1HeapRegionSize   = 0 (0.0MB)

Heap Usage: 堆的使用情况
New Generation (Eden + 1 Survivor Space): 新生代
 capacity = 2899116032 (2764.8125MB)
 used  = 384206560 (366.4079284667969MB)
 free  = 2514909472 (2398.404571533203MB)
 13.25254166301682% used
Eden Space: 新生代 eden区空间
 capacity = 2577006592 (2457.625MB)
 used  = 378654344 (361.11292266845703MB)
 free  = 2198352248 (2096.512077331543MB)
 14.693572968555294% used
From Space: 2个Survivor区域 其中一个就是这个from区
 capacity = 322109440 (307.1875MB)
 used  = 5552216 (5.295005798339844MB)
 free  = 316557224 (301.89249420166016MB)
 1.723704837709817% used
To Space:2个Survivor区域 其中一个就是这个to区
 capacity = 322109440 (307.1875MB)
 used  = 0 (0.0MB)
 free  = 322109440 (307.1875MB)
 0.0% used
concurrent mark-sweep generation: 老年代 eden区空间
 capacity = 1073741824 (1024.0MB)
 used  = 846734040 (807.5085067749023MB)
 free  = 227007784 (216.49149322509766MB)
 78.85825261473656% used

jmap -histo 922
由于里面比较多内容，所以放弃了，可以自己使用一下，如果电脑展示不了一屏呢，可以这样。

jmap -histo 922 >dump.txt 导出文件，可以自己看了
下面是我自己导出的文件信息
 num  #instances(实例数量)   #bytes（字节） class name 
----------------------------------------------
 1:  174069  1579369600 [C
 2:   4403  122732640 [I
 3:   9571  16889072 [B
 4:  157680  3784320 java.lang.String
 5:   38279  3674784 java.util.jar.JarFile$JarFileEntry
 6:   70982  2271424 java.util.HashMap$Node
 7:   13235  1164680 java.lang.reflect.Method
 8:   6001  1028952 [Ljava.util.HashMap$Node;

又或者可以过滤信息，命令：jmap -histo 922 |grep dubbo 过滤一下，就过滤你想要的信息