JVM系列五:JVM监测&工具[整理中]

逃离我推掉我的手 2022-09-17 09:29 173阅读 0赞

前几篇篇文章介绍了介绍了JVM的参数设置并给出了一些生产环境的JVM参数配置参考方案。正如之前文章中提到的JVM参数的设置需要根据应用的特性来进行设置，每个参数的设置都需要对JVM进行长时间的监测，并不断进行调整才能找到最佳设置方案。本文将介绍如果通过工具及Java api来监测JVM的运行状态,并详细介绍各工具的使用方法。

需要监测的数据：(内存使用情况 谁使用了内存 GC的状况)

内存使用情况--heap&PermGen

@ 表示通过jmap –heap pid 可以获取的值

\# 表示通过jstat –gcutil pid 可以获取的值

参数的查看可以通过多种方法 本文中只随机列出一种。

<table style="margin:0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 描述</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 最大值</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 当前值</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 报警值</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 堆内存</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Heap Configuration::MaxHeapSize<br style="margin:0px; padding:0px"> <span style="margin:0px; padding:0px">sum(eden+servivor+old)</span></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <span style="margin:0px; padding:0px">sum(eden+servivor+old)</span></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 自设</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 非堆内存</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> sum(perm+native)</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> &nbsp;</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 无</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Eden</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Eden Space::capacity</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Eden Space::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 无</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Survivor0</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @From Space::capacity</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @From Space::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 无</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Survivor1</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @To Space::capacity</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @To Space::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 无</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> New gen<br style="margin:0px; padding:0px"> (注意区别于<a href="http://www.cnblogs.com/redcreen/archive/2011/05/04/2037057.html" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">Xmn参数设置</a>)</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @New Generation::capacity<br style="margin:0px; padding:0px"> <span style="margin:0px; padding:0px">Eden + 1 Survivor Space</span></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @New Generation::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 无</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Old gen</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @concurrent mark-sweep generation::capacity<br style="margin:0px; padding:0px"> (CMS是对old区的gc,所以此处即表示old gen)</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @concurrent mark-sweep generation::capacity(CMS)::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 自设</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Perm Gen</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Perm Generation::capacity</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Perm Generation::used</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 自设</td> 
  </tr> 
 </tbody> 
</table>

内存使用情况--config

<table style="margin:10px 0px 0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
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   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 描述</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 配置值</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> MaxTenuringThreshold</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> jinfo -flag MaxTenuringThreshold&nbsp;<span style="margin:0px; padding:0px">pid</span></td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> MinHeapFreeRatio</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Heap Configuration::MinHeapFreeRatio</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> MaxHeapFreeRatio</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @Heap Configuration::MaxHeapFreeRatio</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> new gen gc</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> @using … in the new generation</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> old gen gc</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> new gen gc声明下方</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 类总数统计</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> ??</td> 
  </tr> 
 </tbody> 
</table>

内存使用情况—C heap

*  top or ps aux

谁使用了内存

*  Heap  
    jmap –histo  
    jmap –dump ,then mat
 *  C heap  
    google perftools

GC的状况

<table style="margin:10px 0px 0px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
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  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 描述</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 收集次数</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 收集时间</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 应用暂停时间</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Full GC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> #FGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> #FGCT</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/04/2037057.html" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">设置-XX:+PrintGCApplicationStoppedTime</a>后在日志中查看</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Young GC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> #YGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> #YGCT</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 同上</td> 
  </tr> 
 </tbody> 
</table>

\-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC  [\-XX:+PrintGCApplicationStoppedTime][-XX_PrintGCApplicationStoppedTime]  -Xloggc:logs/gc.log

常用[工具][Link 1]介绍:jinfo jmap jstack jstat

[jinfo][]

*  可以从一个给定的java进程或core文件或远程debug服务器上获取java配置信息。包括java系统属性及JVM参数(command line flags)。注意在jvm启动参数中没有配置的参数也可使用jinfo –flag xxx pid输出默认值(很有用,但貌似一些简写的参数查不出来)。
 *  可以修改运行时的java 进程的opts。
 *  只有solaris和linux的JDK版本里有。
 *  使用方式可使用jinfo –h 查询。

[jmap][]

观察运行中的jvm物理内存的占用情况。

如果连用SHELL jmap -histo pid>a.log可以将其保存到文本中去，在一段时间后，使用文本对比工具，可以对比出GC回收了哪些对象。

参数很简单，直接查看jmap -h

举例：

jmap -heap pid jmap -dump:format=b,file=heap.hprof <pid>

dump文件可以通过MemoryAnalyzer分析查看.网址： [http://www.eclipse.org/mat/][http_www.eclipse.org_mat]，可以查看dump时对象数量，内存占用，线程情况等。

[jmap -dump:live为啥会触发Full GC][jmap -dump_live_Full GC]

[jstack][]

观察jvm中当前所有线程的运行情况和线程当前状态

如果java程序崩溃生成core文件，jstack工具可以用来获得core文件的java stack和native stack的信息，从而可以轻松地知道java程序是如何崩溃和在程序何处发生问题。另外，jstack工具还可以附属到正在运行的java程序中，看到当时运行的java程序的java stack和native stack的信息, 如果现在运行的java程序呈现hung的状态，jstack是非常有用的。目前只有在Solaris和Linux的JDK版本里面才有。

参数很简单，直接查看jstack -h

举例：

jstack pid

[jstat][]

JVM监测工具(Java Virtual Machine Statistics Monitoring Tool)。利用了JVM内建的指令对Java应用程序的资源和性能进行实时的命令行的监控，包括各种堆和非堆的大小及其内存使用量、classloader、compiler、垃圾回收状况等。

举例:

jstat –printcompilation -h10 3024 250 600

每250毫秒打印一次，一共打印600次 每隔10行显示一次head

语法结构:

Usage: jstat -help|-options
           jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

参数介绍：

*  \-h n 每隔几行输出标题
 *  vmid VM的进程号，即当前运行的java进程号
 *  \-t 在第一列显示自JVM启动以来的时间戳
 *  \-J 修改java进程的参数。类似jinfo -flag <name>=<value>。例如\-J-Xms48m 设置初始堆为48M。[详见这里][Link 2]。这个参数挺有用的，可以在运行中调整参数以方便测试、监测。
 *  \-option option为要检测的参数。参数列表可通过jstat –options 获取。下面将分别介绍每个参数及输出字段的含义。

<table style="margin:0px 0px 0px 30px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
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   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#class_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">class</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计class loader行为信息</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#compiler_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">compiler</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计编译行为信息</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gc_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gc</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计jdk gc时heap信息</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gccapacity_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gccapacity</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计堆内存不同代的heap容量信息</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gccause_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gccause</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc的情况（同-gcutil）和引起gc的事件</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcnew_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcnew</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时新生代的信息(相比gcutil更详细)</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcnewcapacity_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcnewcapacity</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时新生代heap容量</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcold_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcold</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时，老年区的情况</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcoldcapacity_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcoldcapacity</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时，老年区heap容量</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcpermcapacity_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcpermcapacity</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时，permanent区heap容量</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#gcutil_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">gcutil</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计gc时，heap情况</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <a href="http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html#printcompilation_option" style="margin:0px; padding:0px; color:rgb(100,102,179)" rel="nofollow">printcompilation</a></td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> 统计编译行为信息</td> 
  </tr> 
 </tbody> 
</table>

\-class option:Class Loader Statistics

\-compiler:HotSpot Just-In-Time Compiler Statistics

\-gc Option:Garbage-collected heap statistics

<table style="margin:0px 0px 0px 30px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
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   <th style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <span style="margin:0px; padding:0px">Column</span></th> 
   <th style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <span style="margin:0px; padding:0px">Description</span></th> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S0C</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current survivor space 0 capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S1C</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current survivor space 1 capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S0U</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Survivor space 0 utilization (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S1U</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Survivor space 1 utilization (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> EC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current eden space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> EU</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Eden space utilization (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current old space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OU</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Old space utilization (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current permanent space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PU</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Permanent space utilization (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> YGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Number of young generation GC Events.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> YGCT</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Young generation garbage collection time.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> FGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Number of full GC events.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> FGCT</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Full garbage collection time.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> GCT</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Total garbage collection time.</td> 
  </tr> 
 </tbody> 
</table>

\-gccapacity Option:Memory Pool Generation and Space Capacities

<table style="margin:0px 0px 0px 30px; padding:0px; border-collapse:collapse; border-spacing:0px; border:1px solid silver; color:rgb(57,57,57); font-family:verdana,'ms song',Arial,Helvetica,sans-serif; font-size:14px; line-height:21px; background-color:rgb(250,247,239)"> 
 <tbody style="margin:0px; padding:0px"> 
  <tr style="margin:0px; padding:0px"> 
   <th style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <span style="margin:0px; padding:0px">Column</span></th> 
   <th style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> <span style="margin:0px; padding:0px">Description</span></th> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> NGCMN</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Minimum new generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> NGCMX</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Maximum new generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> NGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current new generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S0C</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current survivor space 0 capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> S1C</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current survivor space 1 capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> EC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current eden space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OGCMN</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Minimum old generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OGCMX</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Maximum old generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current old generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> OC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current old space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PGCMN</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Minimum permanent generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PGCMX</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Maximum Permanent generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current Permanent generation capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> PC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Current Permanent space capacity (KB).</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> YGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Number of Young generation GC Events.</td> 
  </tr> 
  <tr style="margin:0px; padding:0px"> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> FGC</td> 
   <td style="margin:0px; padding:3px; border:1px solid silver; border-collapse:collapse"> Number of Full GC Events.</td> 
  </tr> 
 </tbody> 
</table>

\-gccause Option:Garbage Collection Statistics, Including GC Events

前面的字段与gcutil相同.

\-gcnew Option:New Generation Statistics

\-gcnewcapacity Option:New Generation Space Size Statistics

\-gcold Option:Old and Permanent Generation Statistics

\-gcoldcapacity Option:Old Generation Statistics

\-gcpermcapacity Option: Permanent Generation Statistics

\-gcutil Option:Summary of Garbage Collection Statistics

\-printcompilation Option: HotSpot Compiler Method Statistics

Java api方式监测

jre中提供了一些查看运行中的[jvm][]内部信息的api，这些api包含在java.lang.management包中，此包中的接口是在jdk 5中引入的，所以只有在jdk 5及其以上版本中才能通过这种方式访问这些信息。下面简单介绍一下这包括哪些信息，以及如何访问。

可以通过此api访问到运行中的jvm的类加载的信息、jit编译器的信息、内存分配的情况、线程的相关信息以及运行jvm的操作系统的信息。java.lang.management包中提供了9个接口来访问这些信息，使用ManagementFactory的静态get方法可以获得相应接口的实例，可以通过这些实例来获取你需要的相关信息。

更详细的关于MBean的介绍参见[Java SE 6 新特性: JMX 与系统管理][Java SE 6 _ JMX]

demo1:查看一下当前运行的jvm中加载了多少个类。想详细了解如何使用这些api，可以参考java.lang.management包中的详细api文档。

public class ClassLoaderChecker {
       
        public static void main( String[] args ) throws Exception {
       
          ClassLoadingMXBean bean = ManagementFactory.getClassLoadingMXBean();
          System.out.println( bean.getLoadedClassCount() );
        }
    }

demo2:自定义Mbean Type,记录的数据可通过jconsole等工具或自写代码查看,

//工具方法 public static ObjectName register(String name, Object mbean) {
        
            try {
        
                ObjectName objectName = new ObjectName(name);
    
                MBeanServer mbeanServer = ManagementFactory
                        .getPlatformMBeanServer();
    
                try {
        
                    mbeanServer.registerMBean(mbean, objectName);
                } catch (InstanceAlreadyExistsException ex) {
        
                    mbeanServer.unregisterMBean(objectName);
                    mbeanServer.registerMBean(mbean, objectName);
                } return objectName;
            } catch (JMException e) {
        
                throw new IllegalArgumentException(name, e);
            }
    }
      
       
        
       //步骤一:定义Mbean接口:
      
       
      
       
        
       //随便定义
      
       
      
       
        
       public interface DemoMBean {
      
       
      
       
        
             public AtomicLong getInvokeCount();
      
       
      
       
        
       }
      
       
      
       
        
       //步骤二:实现接口,并注册:
      
       
      
       
        
       public class DemoImpl implements DemoMBean{
      
       
      
       
        
             public final static String DEFAULT_OBJECT_NAME_PREFIX = "com.redcreen.demo:type=demo";
      
       
      
       
        
             register("com.redcreen.demo:type=demo",DemoImpl.instance);
      
       
      
       
        
       }
      
       
      
       
        
       //可以通过jconsole中查看数据了