# 7.3 jmap工具
jmap(Java Virtual Machine Memory Map)是JDK提供的一个可以生成Java虚拟机的堆转储快照dump文件的命令行工具。 除此以外, jmap命令还可以查看finalize执行队列、Java堆和方法区的详细信息, 比如空间使用率、当前使用的什么垃圾回收器、分代情况等等。
# 7.3.1 命令参数
其用法可以通过jmap -help来查看。
MacBook-Pro root$ 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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- -heap
打印Java堆概要信息,包括使用的GC算法、堆配置参数和各代中堆内存使用情况;
- -histo[:live]
显示Java堆中对象的统计信息,包括:对象数量、占用内存大小(单位:字节)和类的完全限定名。比如: