JVM命令-jmap

一、命令概述

jmap 用于生成堆 dump文件，查看堆内对象统计信息、classloader 信息、 finalizer 队列

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

二、示例

1、查看进程的内存映像信息

jmap 28025

2、显示 Java 堆详细信息

jmap -heap 28025

3、显示堆中对象的统计信息（各对象占用大小）
注：最好导出堆快照，用MAT或者Jprofile分析大对象引用。

jmap -histo:live 28025

4、生成堆 dump 文件
注：dump内存快照时，会对服务造成一定影响，线上慎用。

jmap -dump:format=b,file=heapdump.hprof 28025

本文转载自：http://mousycoder.com/thinking-in-jvm/46/