前言
大家都知道有很多开源的监控工具，本次只使用了jmap，了解简单使用，谢谢，下面话不多说了，来一起看看详细的介绍吧
使用方法如下：
开始了，922是我的tomcat进程
帮助命令查看，有哪些命令可以使用。
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[root@bogon /]# jmap -help
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
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使用1：jmap pid 查看基本信息
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[root@bogon /]# jmap 922
attaching to process id 922, please wait...
debugger attached successfully.
server compiler detected.
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
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使用2 ：查看堆信息，jmap -heap pid
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[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
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使用3：jmap -histo pid 查看一些class的使用情况，
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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
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使用4：jmap -histo:live pid >dump.txt
这个和使用3差不多，都是在统计，只不过这个是在统计正在使用的对象，然后dump对象信息。
这种命令都是结合其它的命令一起使用的，以后会有文章结合一起分析，同学有什么好的工具也分享出来，一起学习，本篇只介绍jmap
总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对服务器之家的支持。
原文链接：http://blog.51cto.com/shangdc/2151219