5. jstat -gcutil 2208 1000(每隔1000毫秒打印一次信息) 10（打印10行）
C:UsersWILL>jstat
invalid argument count
Usage: jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]
Definitions:
<option>      An option reported by the -options option
<vmid>        Virtual Machine Identifier. A vmid takes the following form:
<lvmid>[@<hostname>[:<port>]]
Where <lvmid> is the local vm identifier for the target
Java virtual machine， typically a process id; <hostname> is
the name of the host running the target Java virtual machine;
and <port> is the port number for the rmiregistry on the
target host. See the jvmstat documentation for a more complete
description of the Virtual Machine Identifier.
<lines>       Number of samples between header lines.
<interval>    Sampling interval. The following forms are allowed:
<n>["ms"|"s"]
Where <n> is an integer and the suffix specifies the units as
milliseconds("ms") or seconds("s"). The default units are "ms".
<count>       Number of samples to take before terminating.
-J<flag>      Pass <flag> directly to the runtime system.
　　C:UsersWILL>jstat -options
　　-class
　　-compiler
　　-gc
　　-gccapacity
　　-gccause
　　-gcnew
　　-gcnewcapacity
　　-gcold
　　-gcoldcapacity
　　-gcpermcapacity
　　-gcutil
　　-printcompilation
　　6. jmap把虚拟机里运行着的所有文件都down下来，相当于快照
C:UsersWILL>jmap
Usage:
jmap -histo <pid>
(to connect to running process and print histogram of java object heap
jmap -dump:<dump-options> <pid>
(to connect to running process and dump java heap)
dump-options:
format=b     binary default
file=<file>  dump heap to <file>
Example:       jmap -dump:format=b，file=heap.bin <pid>
　　7. jhat 对jmap下来的文件进行分析，多个角度
Usage:  jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-
debug <int>] [-version] [-h|-help] <file>
-J<flag>          Pass <flag> directly to the runtime system. For
example， -J-mx512m to use a maximum heap size of 512MB
-stack false:     Turn off tracking object allocation call stack.
-refs false:      Turn off tracking of references to objects
-port <port>:     Set the port for the HTTP server.  Defaults to 7000
-exclude <file>:  Specify a file that lists data members that should
be excluded from the reachableFrom query.
-baseline <file>: Specify a baseline object dump.  Objects in
both heap dumps with the same ID and same class will
be marked as not being "new".
-debug <int>:     Set debug level.
0:  No debug output
1:  Debug hprof file parsing
2:  Debug hprof file parsing， no server
-version          Report version number
-h|-help          Print this help and exit
<file>            The file to read
For a dump file that contains multiple heap dumps，
you may specify which dump in the file
by appending "#<number>" to the file name， i.e. "foo.hprof#3".
All boolean options default to "true"
　　图片又不能上传。。。打印出这些帮助参数来，能看懂得了。