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<h1 class="title" id="leanote-title">java常用工具的作用及用法</h1>
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<div class="content-html" id="leanote-content"><div><strong><span color="#ff0000" data-mce-style="color: #ff0000;" style="color: #ff0000;">jstatd</span></strong><br></div><div>启动jvm监控服务。它是一个基于rmi的应用，向远程机器提供本机jvm应用程序的信息。默认端口1099。<br></div><div>实例：jstatd -J-Djava.security.policy=my.policy<br><br>my.policy文件需要自己建立，内如如下：<br>grant codebase "file=$JAVA_HOME/lib/tools.jar" {<br>permission java.security.AllPermission;<br>};<br>这是安全策略文件，因为jdk对jvm做了jaas的安全检测，所以我们必须设置一些策略，使得jstatd被允许作网络操作<br></div><div><br></div><div><span color="#ff0000" data-mce-style="color: #ff0000;" style="color: #ff0000;"><strong>jps</strong></span><br>列出所有的jvm实例<br>实例：<br>jps<br>列出本机所有的jvm实例<br><br>jps 192.168.0.77<br>列出远程服务器192.168.0.77 机器所有的jvm实例，采用rmi协议，默认连接端口为1099<br>（前提是远程服务器提供jstatd服务）<br><br>输出内容如下：<br>jones@jones:~/data/ebook/java/j2se/jdk_gc$ jps<br>6286 Jps<br>6174 <wbr> <wbr>Jstat<br><br></div><p><strong><span color="#ff0000" face="Tahoma, Microsoft Yahei, simsun" data-mce-style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;" style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;">jconsole</span></strong></p><div><br>一个图形化界面，可以观察到java进程的 gc，class，内存等信息。虽然比较直观，但是个人还是比较倾向于使用jstat命令（在最后一部分会对jstat作详细的介绍）。<br><br></div><p><strong><span color="#ff0000" face="Tahoma, Microsoft Yahei, simsun" data-mce-style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;" style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;">jinfo</span></strong></p><div>（linux下特有）<br>观察运行中的java程序的运行环境参数：参数包括Java System属性和JVM命令行参数<br>实例：jinfo 2083<br>其中2083 就是java进程id号，可以用jps得到这个id号。<br>输出内容太多了，不在这里一一列举，大家可以自己尝试这个命令。<br><br></div><p><strong><span color="#ff0000" face="Tahoma, Microsoft Yahei, simsun" data-mce-style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;" style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;">jstack</span></strong></p><div>（linux下特有）<br>可以观察到jvm中当前所有线程的运行情况和线程当前状态<br>jstack 2083<br>jmap（linux下特有，也是很常用的一个命令）<br>观察运行中的jvm物理内存的占用情况。<br>参数如下：<br>-heap：打印jvm heap的情况<br>-histo：打印jvm heap的直方图。其输出信息包括类名，对象数量，对象占用大小。<br>-histo：live ：同上，但是只答应存活对象的情况<br>-permstat：打印permanent generation heap情况<br><br>命令使用：<br>jmap -heap 2083<br>可以观察到New Generation（Eden Space，From Space，To Space）,tenured generation,Perm Generation的内存使用情况<br><br>jmap -histo 2083 ｜ jmap -histo:live 2083<br>可以观察 heap中所有对象的情况（heap中所有生存的对象的情况）。包括对象数量和所占空间大小。<br><br>写个脚本，可以很快把占用heap最大的对象找出来，对付内存泄漏特别有效。<br><br></div><p><strong><span color="#ff0000" face="Tahoma, Microsoft Yahei, simsun" data-mce-style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;" style="color: #ff0000; font-family: Tahoma, 'Microsoft Yahei', simsun;">jstat</span></strong></p><div><br>最后要重点介绍下这个命令。<br>这是jdk命令中比较重要，也是相当实用的一个命令，可以观察到classloader，compiler，gc相关信息<br>具体参数如下：<br>-class：统计class loader行为信息<br>-compile：统计编译行为信息<br>-gc：统计jdk gc时heap信息<br>-gccapacity：统计不同的generations（不知道怎么翻译好，包括新生区，老年区，permanent区）相应的heap容量情况<br>-gccause：统计gc的情况，（同-gcutil）和引起gc的事件<br>-gcnew：统计gc时，新生代的情况<br>-gcnewcapacity：统计gc时，新生代heap容量<br>-gcold：统计gc时，老年区的情况<br>-gcoldcapacity： 统计gc时，老年区heap容量<br>-gcpermcapacity：统计gc时，permanent区heap容量<br>-gcutil：统计 gc时，heap情况<br>-printcompilation：不知道干什么的，一直没用过。<br><br>一般比较常用的几个参数是：<br>jstat -class 2083 1000 10 （每隔1秒监控一次，一共做10次）<br>输出内容含义如下：<br>Loaded <wbr> <wbr> <wbr> <wbr> Number of classes loaded.<br>Bytes <wbr> <wbr> <wbr> <wbr> Number of Kbytes loaded.<br>Unloaded <wbr> <wbr> <wbr> <wbr> Number of classes unloaded.<br>Bytes <wbr> <wbr> <wbr> <wbr> Number of Kbytes unloaded.<br>Time <wbr> <wbr> <wbr> <wbr> Time spent performing class load and unload operations.<br><br><br>jstat -gc 2083 2000 20（每隔2秒监控一次，共做10）<br>输出内容含义如下：<br>S0C <wbr> <wbr> <wbr> <wbr> Current survivor（存活的） space 0 capacity (KB).<br>EC <wbr> <wbr> <wbr> <wbr> Current eden space capacity (KB).<br>EU <wbr> <wbr> <wbr> <wbr> Eden space utilization (KB).<br>OC <wbr> <wbr> <wbr> <wbr> Current old space capacity (KB).<br>OU <wbr> <wbr> <wbr> <wbr> Old space utilization (KB).<br>PC <wbr> <wbr> <wbr> <wbr> Current permanent space capacity (KB).<br>PU <wbr> <wbr> <wbr> <wbr> Permanent space utilization (KB).<br>YGC <wbr> <wbr> <wbr> <wbr> Number of young generation GC Events.<br>YGCT <wbr> <wbr> <wbr> <wbr> Young generation garbage collection time.<br>FGC <wbr> <wbr> <wbr> <wbr> Number of full GC events.<br>FGCT <wbr> <wbr> <wbr> <wbr> Full garbage collection time.<br>GCT <wbr> <wbr> <wbr> <wbr> Total garbage collection time.<br><br><br>监控内存使用情况 参数 （查看内存溢出相对有用）<br><br>jstat -gccause 2083 5000 （每隔5秒监控一次）<br>输出内容含义如下：<br><br>S0 <wbr> <wbr> <wbr> <wbr> Survivor space 0 utilization as a percentage of the space's current capacity.<br>S1 <wbr> <wbr> <wbr> <wbr> Survivor space 1 utilization as a percentage of the space's current capacity.<br>E <wbr> <wbr> <wbr> <wbr> Eden space utilization as a percentage of the space's current capacity.<br>O <wbr> <wbr> <wbr> <wbr> Old space utilization as a percentage of the space's current capacity.<br>P <wbr> <wbr> <wbr> <wbr> Permanent space utilization as a percentage of the space's current capacity.<br>YGC <wbr> <wbr> <wbr> <wbr> Number of young generation GC events.<br>YGCT <wbr> <wbr> <wbr> <wbr> Young generation garbage collection time.<br>FGC <wbr> <wbr> <wbr> <wbr> Number of full GC events.<br>FGCT <wbr> <wbr> <wbr> <wbr> Full garbage collection time.<br>GCT <wbr> <wbr> <wbr> <wbr> Total garbage collection time.<br>LGCC <wbr> <wbr> <wbr> <wbr> Cause of last Garbage Collection.<br>GCC <wbr> <wbr> <wbr> <wbr> Cause of current Garbage Collection.<br></div><p><br></p></div>
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