java自带命令行工具(jcmd,jstack)

1.jcmd
1.1作用
发送诊断命令请求到正在运行的Java虚拟机（JVM）。

它必须和JVM运行在同一台机器上，并且与启动JVM用户具有相同的组权限。
1.2语法

jcmd [-l|-h|-help]
jcmd pid|main-class PerfCounter.print
jcmd pid|main-class -f filename
jcmd pid|main-class command[ arguments]

Perfcounter.print：打印Java进程的性能计数器
-f filename：从中读取诊断命令，每行命令必须在一行内写完
command [arguments]：诊断指令

1.3命令列表

C:\Users\Administrator>jcmd 7048 help
7048:
The following commands are available:
VM.native_memory
VM.commercial_features
ManagementAgent.stop
ManagementAgent.start_local
ManagementAgent.start
Thread.print
GC.class_histogram
GC.heap_dump
GC.run_finalization
GC.run
VM.uptime
VM.flags
VM.system_properties
VM.command_line
VM.version

#打印JDK及版本
C:\Users\Administrator>jcmd 7048 VM.version
7048:
Java HotSpot(TM) 64-Bit Server VM version 24.75-b04
JDK 7.0_75
#打印虚拟机系统属性
可以有几百行的信息显示。

C:\Users\Administrator>jcmd 7048  VM.system_properties
7048:
#Sat Apr 15 21:24:31 CST 2017
java.runtime.name=Java(TM) SE Runtime Environment
sun.boot.library.path=D\:\\Java\\jdk1.7.0_75\\jre\\bin
java.vm.version=24.75-b04
shared.loader=
java.vm.vendor=Oracle Corporation
java.vendor.url=http\://java.oracle.com/
path.separator=;
java.vm.name=Java HotSpot(TM) 64-Bit Server VM
tomcat.util.buf.StringCache.byte.enabled=true
file.encoding.pkg=sun.io
...
#打印用于虚拟机的所有标志
即使没有设置，一些默认值将被打印出来
C:\Users\Administrator>jcmd 7048 VM.flags
7048:
-XX:InitialHeapSize=132669696 -XX:MaxHeapSize=2124414976 -XX:+UseCompressedOops
-XX:-UseLargePagesIndividualAllocation -XX:+UseParallelGC

7048:
[Global flags]
uintx AdaptivePermSizeWeight                    = 20              {product}
uintx AdaptiveSizeDecrementScaleFactor          = 4               {product}
uintx AdaptiveSizeMajorGCDecayTimeScale         = 10              {product}
uintx AdaptiveSizePausePolicy                   = 0               {product}
uintx AdaptiveSizePolicyCollectionCostMargin    = 50              {product}
uintx AdaptiveSizePolicyInitializingSteps       = 20              {product}
uintx AdaptiveSizePolicyOutputInterval          = 0               {product}
uintx AdaptiveSizePolicyWeight                  = 10              {product}
uintx AdaptiveSizeThroughPutPolicy              = 0               {product}
uintx AdaptiveTimeWeight                        = 25              {product}
bool AdjustConcurrency                         = false           {product}
bool AggressiveOpts                            = false           {product}
intx AliasLevel                                = 3               {C2 product}
bool AlignVector                               = true            {C2 product}
uintx InitialHeapSize                          := 132669696       {product}
...
#冒号：表示非默认值
#打印(秒)正常运行时间
C:\Users\Administrator>jcmd 7048 VM.uptime
7048:
2213.664 s
#类直方图
C:\Users\Administrator>jcmd 7048 GC.class_histogram   > 12333.txt
7048:
num     #instances         #bytes  class name
----------------------------------------------
1:         11678        8137440  [B
2:         30213        4300992  [C
3:         28188        3966976  <constMethodKlass>
4:         28188        3619568  <methodKlass>
5:          2339        2866712  <constantPoolKlass>
6:          2038        1698944  <constantPoolCacheKlass>
7:          2339        1659448  <instanceKlassKlass>
8:         28718         689232  java.lang.String
9:         16608         531456  java.util.HashMap$Entry
10:           736         416896  <methodDataKlass>
11:          6144         369080  [Ljava.lang.Object;
12:          2620         254960  java.lang.Class
13:           877         234768  [Ljava.util.HashMap$Entry;
14:          3569         229624  [S
15:          3773         214248  [[I
....
#创建堆转储（HPROF）
C:\Users\Administrator>jcmd 7048 GC.heap_dump filename=Myheapdump
7048:
Heap dump file created
与jmap -dump:file=<file> <pid>功能一样
#创建一个堆直方图
jcmd <process id/main class> GC.class_histogram filename=Myheaphistogram
使用jmap -histo <pid>
打印线程的栈信息
C:\Users\Administrator>jcmd  7048 Thread.print
7048:
2017-04-15 21:43:28
Full thread dump Java HotSpot(TM) 64-Bit Server VM (24.75-b04 mixed mode):

"ajp-bio-8009-AsyncTimeout" daemon prio=6 tid=0x000000000d5bb000 nid=0x78c waiting on condition [0x000000000f16f000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at org.apache.tomcat.util.net.JIoEndpoint$AsyncTimeout.run(JIoEndpoint.java:152)
at java.lang.Thread.run(Thread.java:745)
.......

{product}

{C2 product}

{pd product}

{C1 product}

{manageable}：运行时动态更改

{C2 pd product}

{ARCH product}

{C1 pd product}

{lp64_product}

{product rw}

(2)jstack

2.1 作用

打印Java进程，核心文件或者远程调试服务器的Java线程堆栈跟踪.
死锁监测和HANG

使用jsadebugd 守护进程查询远程机器上的core文件及进程

-l,可以打印java.util.concurrent.locks同步信息和堆上的同步器，没有该选项，仅仅是监视器的信息。

jstack pid 与 ctrl+break

也可以Thread.getAllStackTraces

2.2 语法

jstack [ options ] pid
jstack [ options ] executable core
jstack [ options ] [ server-id@ ] remote-hostname-or-IP

每一个栈帧，打印信息包括类名，方法名，字节码索引（BCI），和行数。-m开关，同时打印本地和java栈帧信息。
当指定的进程在一个64位Java虚拟机上运行，则可能需要指定-J-d64选项，例如：jstack -J-d64 -m pid。
2.3 参数Options
-F：强制dump
-l：打印额外信息
-m：打印混合堆栈信息(c++,java)
http://docs.oracle.com/javase/8/docs/technotes/tools/unix/jstack.html http://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr016.html https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr006.html https://docs.oracle.com/javase/8/docs/technotes/tools/windows/jcmd.html https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr006.html