[zz]JDK自带VM分析工具jps，jstat，jmap，jconsole

little lily posted @ Tue, 31 Aug 2010 18:33:52 +0800 in Testing with tags jconsle jps jstat jmap , 1689 readers

zz from http://jiajun.javaeye.com/blog/443196

一、概述  

 

 

    SUN 的JDK中的几个工具，非常好用。秉承着有免费，不用商用的原则。以下简单介绍一下这几种工具。(注：本文章下的所有工具都存在JDK5.0以上版本的工具集里，同javac一样，不须特意安装)  。
      
    我一共找到以下四个工具：重点看看jconsole和jmap。

Java代码 
  1. jps  
  2. :与unix上的ps类似，用来显示本地的java进程，可以查看本地运行着几个java程序，并显示他们的进程号。   
  3.   
  4. jstat  
  5. :一个极强的监视VM内存工具。可以用来监视VM内存内的各种堆和非堆的大小及其内存使用量。   
  6.   
  7. jmap  
  8. :打印出某个java进程（使用pid）内存内的，所有‘对象’的情况（如：产生那些对象，及其数量）。   
  9.   
  10. jconsole  
  11. :一个java GUI监视工具，可以以图表化的形式显示各种数据。并可通过远程连接监视远程的服务器VM。  

 

二、 使用介绍：  
      
    1、jstat ：我想很多人都是用过unix系统里的ps命令，这个命令主要是用来显示当前系统的进程情况，有哪些进程，及其 id。 jps 也是一样，它的作用是显示当前系统的java进程情况，及其id号。我们可以通过它来查看我们到底启动了几个java进程（因为每一个java程序都会独占一个java虚拟机实例），和他们的进程号（为下面几个程序做准备），并可通过opt来查看这些进程的详细启动参数。  
    使用方法：在当前命令行下打 jps(需要JAVA_HOME，没有的话，到改程序的目录下打) 。

可惜没有linux下的ps好用，名称不好用。但是在第四个工具jconsole的界面里面会有具体JAR包的名称。
      
    2、jstat ：对VM内存使用量进行监控。  
    jstat工具特别强大，有众多的可选项，详细查看堆内各个部分的使用量，以及加载类的数量。使用时，需加上查看进程的进程id，和所选参数。以下详细介绍各个参数的意义。  
    jstat -class pid:显示加载class的数量，及所占空间等信息。  
    jstat -compiler pid:显示VM实时编译的数量等信息。  
    jstat -gc pid:可以显示gc的信息，查看gc的次数，及时间。其中最后五项，分别是young gc的次数，young gc的时间，full gc的次数，full gc的时间，gc的总时间。  
    jstat -gccapacity:可以显示，VM内存中三代（young,old,perm）对象的使用和占用大小，如：PGCMN显示的是最小perm的内存使用量，PGCMX显示的是perm的内存最大使用量，PGC是当前新生成的perm内存占用量，PC是但前perm内存占用量。其他的可以根据这个类推， OC是old内纯的占用量。  
    jstat -gcnew pid:new对象的信息。  
    jstat -gcnewcapacity pid:new对象的信息及其占用量。  
    jstat -gcold pid:old对象的信息。  
    jstat -gcoldcapacity pid:old对象的信息及其占用量。  
    jstat -gcpermcapacity pid: perm对象的信息及其占用量。  
    jstat -util pid:统计gc信息统计。  
    jstat -printcompilation pid:当前VM执行的信息。  
    除了以上一个参数外，还可以同时加上 两个数字，如：jstat -printcompilation 3024 250 6是每250毫秒打印一次，一共打印6次，还可以加上-h3每三行显示一下标题。  
      
   3、jmap 是一个可以输出所有内存中对象的工具，甚至可以将VM 中的heap，以二进制输出成文本。使用方法 jmap -histo pid。如果连用 SHELL jmap -histo pid>a.log可以将其保存到文本中去（windows下也可以使用），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。jmap -dump:format=b,file=f1 3024可以将3024进程的内存heap输出出来到f1文件里。  
      
    4、jconsole 是一个用java写的GUI程序，用来监控VM，并可监控远程的VM，非常易用，而且功能非常强。由于是GUI程序，这里就不详细介绍了，不会的地方可以参考ＳＵＮ的官方文档。  
    使用方法：命令行里打 jconsole，选则进程就可以了。  
      
    友好提示：windows查看进程号，由于任务管理器默认的情况下是不显示进程id号的，所以可以通过如下方法加上。ctrl+alt+del打开任务管理器，选择‘进程’选项卡，点‘查看’->''选择列''->加上''PID''，就可以了。当然还有其他很好的选项。

 

三、参考资料：

    article:http://elf8848.javaeye.com/blog/442806


    jps:http://java.sun.com/j2se/1.5.0/docs/tooldocs/share/jps.html 


    jstat:http://java.sun.com/j2se/1.5.0/docs/tooldocs/share/jstat.html 


    jmap:http://java.sun.com/j2se/1.5.0/docs/tooldocs/share/jmap.html 


    jconsole:http://java.sun.com/j2se/1.5.0/docs/guide/management/jconsole.html       

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