如果大家使用的是maven工程Q那么现?/span>pom文g中加?/span>perf4j的依赖?/span>
<dependency>
<groupId>org.perf4j</groupId>
<artifactId>perf4j</artifactId>
<version>0.9.16</version>
<scope>compile</scope>
</dependency>
如果用的是普通工E，那么直接下蝲jar包放?/span>lib目录下即可?/span>
例子Q?/span>
package com.baowu.per4j;
import org.perf4j.LoggingStopWatch;
import org.perf4j.StopWatch;
public class Example1 {
public static void main(String[] args) throws InterruptedException{
method1();
method2();
method3();
}
/**
* 监控一处代码示?/span>
* @throws InterruptedException
*/
private static void method1() throws InterruptedException{
//创徏一个监控对象，q里使用LoggingStopWatchQ它是把l果直接输出到控制台。我们也可以
//使用StopWatch的其他子c，比如Q?/span>Log4JStopWatchQ?/span>CommonsLogStopWatch。不q这些子c需
//要工E用日志框?/span>
StopWatch stopWatch = new LoggingStopWatch("codeBlock1");
//q里是一些需要监控的代码Q我们命名ؓcodeBlock1
//使用U程休眠是ؓ了模拟代码执行时?/span>
Thread.sleep((long)(Math.random() * 1000L));
//停止计算代码性能
stopWatch.stop();
}
/**
* 一个方法多Z码监?/span>
* @throws InterruptedException
*/
private static void method2() throws InterruptedException{
StopWatch stopWatch = new LoggingStopWatch();
Thread.sleep((long)(Math.random() * 1000L));
stopWatch.lap("codeBlock3");
Thread.sleep((long)(Math.random() * 1000L));
stopWatch.lap("codeBlock4");
Thread.sleep((long)(Math.random() * 1000L));
stopWatch.lap("codeBlock5");
Thread.sleep((long)(Math.random() * 1000L));
stopWatch.stop("codeBlock6");
}
/**
* stopҎ(gu)可以加入一些说明信?/span>
*/
private static void method3(){
StopWatch stopWatch = new LoggingStopWatch();
try {
// the code block being timed - this is just a dummy example
long sleepTime = (long)(Math.random() * 1000L);
Thread.sleep(sleepTime);
if (sleepTime > 500L) {
throw new Exception("Throwing exception");
}
stopWatch.stop("codeBlock2.success", "Sleep time was < 500 ms");
} catch (Exception e) {
stopWatch.stop("codeBlock2.failure", "Exception was: " + e);
}
}
}
q行l果Q?/span>
start[1334457619937] time[355] tag[codeBlock1]
start[1334457620296] time[152] tag[codeBlock3]
start[1334457620453] time[138] tag[codeBlock4]
start[1334457620593] time[598] tag[codeBlock5]
start[1334457621187] time[700] tag[codeBlock6]
start[1334457621890] time[619] tag[codeBlock2.failure] message[Exception was: java.lang.Exception: Throwing exception]
]]>- Perf4j?/title><link>http://www.aygfsteel.com/yangpingyu/archive/2012/04/15/374215.html</link><dc:creator>yangpingyu</dc:creator><author>yangpingyu</author><pubDate>Sun, 15 Apr 2012 02:15:00 GMT</pubDate><guid>http://www.aygfsteel.com/yangpingyu/archive/2012/04/15/374215.html</guid><wfw:comment>http://www.aygfsteel.com/yangpingyu/comments/374215.html</wfw:comment><comments>http://www.aygfsteel.com/yangpingyu/archive/2012/04/15/374215.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/yangpingyu/comments/commentRss/374215.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/yangpingyu/services/trackbacks/374215.html</trackback:ping><description><![CDATA[<div> <p><span style="font-family: 宋体;"></span>Perf4j<span style="font-family: 宋体;">主要的用途是计量代码性能和分析性能数据?/span></p> <p> </p> <p><span style="font-family: 宋体;">Z么要使用q个工具呢？我们可以联想下最早期</span>java<span style="font-family: 宋体;">开发者调试代码用的方式Q以前没有日志框Ӟ?/span>java<span style="font-family: 宋体;">开发就使用</span>System.out.println()<span style="font-family: 宋体;">来输己想查看的变量。但是这样项目上U的话，pLq些打印语句以减性能影响。那万一在线上出问题了，调试哪里出问题就很麻烦，因ؓ没有输出的日志可查。所以后来有人开发了日志框架Q通过日志U别控制日志的输出?/span></p> <p> </p> <p><span style="font-family: 宋体;">cM的，如果没有</span>perf4j<span style="font-family: 宋体;">Q我们在查看代码q行旉的话可以用以下代码来实现Q?/span></p> <p>long start = System.currentTimeMillis();</p> <p>// execute the block of code to be timed</p> <p><span>System.out.println("ms for block n was: " + (System.currentTimeMillis() - start));</span></p> <p><span style="font-family: 宋体;">q种方式有几个缺点：</span></p> <p style="margin-left: 18pt; text-indent: -18pt;"><span>1?nbsp;</span><span style="font-family: 宋体;">q种方式输出内容比较单一Q就是代码ȝq行旉。但是我们代码需要查看的性能指标有更多，比如ȝq_|最|最大|</span>tps<span style="font-family: 宋体;">{等?/span></p> <p style="margin-left: 18pt; text-indent: -18pt;"><span>2?nbsp;</span><span style="font-family: 宋体;">也许我们的代码在U上q行Q我们想把这些值通过图表的Ş式展C出来。或者把q些内容通过</span>jmx<span style="font-family: 宋体;">输出?/span></p> <p style="margin-left: 18pt; text-indent: -18pt;"><span>3?nbsp;</span><span style="font-family: 宋体;">另外Q我们可能把</span>perf4j<span style="font-family: 宋体;">?/span>log4j<span style="font-family: 宋体;">Q?/span>slf4j<span style="font-family: 宋体;">{日志框架和日志门面pȝ整合h?/span></p> <p> </p> <p><span style="font-family: 宋体;">Z以上q些问题Q所以开源社区就出现?/span>perf4j<span style="font-family: 宋体;">Qh多力量大Q社区的力量是强大Q?/span></p> <p>Perf4j<span style="font-family: 宋体;">一些特性：</span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span><span style="font-family: 宋体;">单的停止查看机制来计语句时间消耗输出?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span><span style="font-family: 宋体;">命o行解?/span>log<span style="font-family: 宋体;">文g产生汇L据和图表?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span><span style="font-family: 宋体;">单的集成日志框架和门面框架?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span><span style="font-family: 宋体;">自定?/span>log4j<span style="font-family: 宋体;">?/span>logback<span style="font-family: 宋体;">?/span>appenders<span style="font-family: 宋体;">来生数据和图表?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span><span style="font-family: 宋体;">通过</span>jmx<span style="font-family: 宋体;">查看性能指标QƈҎ(gu)阈值发送消息?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span>Web<span style="font-family: 宋体;">工程可以通过</span>servlet<span style="font-family: 宋体;">来输出性能指标?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span>Perf4j<span style="font-family: 宋体;">可以?/span>aop<span style="font-family: 宋体;">{切面框架整合v来输出性能指标?/span></p> <p style="margin-left: 21pt; text-indent: -21pt;"><span style="font-family: Wingdings;">l </span>Perf4j<span style="font-family: 宋体;">是一个可扩展的架构?/span></p> </div><img src ="http://www.aygfsteel.com/yangpingyu/aggbug/374215.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/yangpingyu/" target="_blank">yangpingyu</a> 2012-04-15 10:15 <a href="http://www.aygfsteel.com/yangpingyu/archive/2012/04/15/374215.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>Maven与findbugshttp://www.aygfsteel.com/yangpingyu/archive/2012/04/14/374180.htmlyangpingyuyangpingyuSat, 14 Apr 2012 10:55:00 GMThttp://www.aygfsteel.com/yangpingyu/archive/2012/04/14/374180.htmlhttp://www.aygfsteel.com/yangpingyu/comments/374180.htmlhttp://www.aygfsteel.com/yangpingyu/archive/2012/04/14/374180.html#Feedback0http://www.aygfsteel.com/yangpingyu/comments/commentRss/374180.htmlhttp://www.aygfsteel.com/yangpingyu/services/trackbacks/374180.html
公司最q严抓Y件质量问题，我抽IZ解了下提高代码质量的一些开源工兗其中一个就?/span>findbugs。?/span>findbugs有很多方式，比如Q安?/span>eclipse findbugs插gQ通过maven调用生成报告。今天主要演CZmaven?/span>findbugs集成?/span>
W一步：下蝲mavenQ我使用的是maven3。把maven的命令加?/span>PATH环境变量?/span>
W二步：创徏一个普通的maven java工程。命令如下：mvn archetype:maven-archetyp-quickstart –DgroupId=com.tianya –DartifactId=baowu。如果正常执行的话会生成如下l构的一个工E?/span>
W三步：我们看下pom文g
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.tianya</groupId>
<artifactId>baowu</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<!--配置插g来源 -->
<pluginRepositories>
<pluginRepository>
<id>Codehaus repository</id>
<url>http://repository.codehaus.org/</url>
</pluginRepository>
</pluginRepositories>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>findbugs-maven-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<!-- <configLocation>${basedir}/springside-findbugs.xml</configLocation> -->
<threshold>High</threshold>
<effort>Default</effort>
<findbugsXmlOutput>true</findbugsXmlOutput>
<!-- findbugs xml输出路径--> <findbugsXmlOutputDirectory>target/site</findbugsXmlOutputDirectory>
</configuration>
</plugin>
</plugins>
</build>
</project>
我来解释?/span>xml配置Q?/span>
l 配置插g下蝲地址
<!--配置插g来源 -->
<pluginRepositories>
<pluginRepository>
<id>Codehaus repository</id>
<url>http://repository.codehaus.org/</url>
</pluginRepository>
</pluginRepositories>
l ׃maven核心做的事情都是抽象的构E，很多实际的工作都是具体的插g来实现。所以很昄Q?/span>maven以插件的方式集成findbugs?/span>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>findbugs-maven-plugin</artifactId>
<version>2.3.2</version>
<configuration>
<!-- <configLocation>${basedir}/springside-findbugs.xml</configLocation> -->
<!-- findbugs xml输出--> <findbugsXmlOutput>true</findbugsXmlOutput>
<!-- findbugs xml输出路径--> <findbugsXmlOutputDirectory>target/site</findbugsXmlOutputDirectory>
</configuration>
</plugin>
l 大家注意Cfindbugs插g里，我注释掉了一句话Q其实这句话是可以使用自己?/span>fingbugs配置来做查。我用的?/span>springside的一?/span>xml文g?/span>
W四步：配置好相x件之后，接下来就是执行相兛_令了?/span>
mvn compile findbugs:findbugs生成报告。报告生成的地址是${目根目?/span>}/target/site。也可以通过mvn findbugs:gui gui界面查看findbugs?/span>report?/span>
]]> - 学习书单和资?/title><link>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369530.html</link><dc:creator>yangpingyu</dc:creator><author>yangpingyu</author><pubDate>Tue, 07 Feb 2012 05:45:00 GMT</pubDate><guid>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369530.html</guid><wfw:comment>http://www.aygfsteel.com/yangpingyu/comments/369530.html</wfw:comment><comments>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369530.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/yangpingyu/comments/commentRss/369530.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/yangpingyu/services/trackbacks/369530.html</trackback:ping><description><![CDATA[<div> <p style="text-indent:21.0pt"><span style="font-family:宋体;">从学校毕业到工作已经</span>2<span style="font-family:宋体;">q半旉了，在豆瓣、当当、京东和亚玛逊上x了很多书c，也比较喜Ƣ逛书店。当然买了很多和看了部分Q自己家里很多书q没看（人类的惰性，借口Q。在q两q半旉内，C一些弯路，所以想ȝ下自q学习生?/span></p> <p style="text-indent:21.0pt"> </p> <p style="text-indent:21.0pt"><span style="font-family:宋体;">毕业的时候去了一家创业型的互联网公司Q在q家公司没有M培训机制QQ何东襉K需要靠自己来捉摸。根据工作需要看?/span>struts2<span style="font-family:宋体;">Q?/span>spring<span style="font-family:宋体;">Q?/span>hibernate<span style="font-family:宋体;">Q?/span>jstl<span style="font-family:宋体;">Q?/span>jsp<span style="font-family:宋体;">Q?/span>servlet<span style="font-family:宋体;">{一?/span>J2EE<span style="font-family:宋体;">相关lg的书和资料。仅靠这些技术也能搭建出一个符合品的|站。接触到</span>infoq<span style="font-family:宋体;">|站之后Q了解了一些大型网站的架构变迁{技术，在一q的旉内不断追寻这些不W合自己目前需要的技术，充其量就是开阔了自己技术的眼界。由于互联网公司的一些劣势，D我有了蟩槽的xQ但是出去面试之后，才知道自己是井底之蛙。自׃热爱技术，也算努力学习和研I的Q自己反思和ȝ了一下：<strong><span style="color:red">不注重基?/span></strong></span></p> <p style="text-indent:21.0pt"> </p> <p style="text-indent:21.0pt"><span style="font-family:宋体;">那么学习什么才基呢？我主要列举下我的学习书单Q?/span></p> <p><span> </span></p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">计算机基QQ何Y件运行的基础?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>深入理解计算机系l（修订版）</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>计算机组成原<span>?/span></span></span></a></p> <p> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">操作pȝQ硬件管理的软gQ我们的应用软g主要依赖于操作系l?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>鸟哥?/span>Linux<span style="font-family:宋体;">U房?/span> <span style="font-family:宋体;">基础学习?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>操作pȝ原理</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Linux<span style="font-family:宋体;"><span>内核设计与实?/span></span></a></p> <p> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">数据l构QY?/span>=<span style="font-family:宋体;">数据l构</span>+<span style="font-family:宋体;">法。其实操作系lY件和应用软g都在大量应用数据l构?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>大话数据l构</span></span></a></p> <p style="margin-left:21.0pt"> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">|络Q系l一定需要与外部交互Q那需要网l?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>计算机网l?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >TCP/IP<span style="font-family:宋体;"><span>详解</span> <span style="font-family:宋体;">?/span>1</span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >TCP/IP<span style="font-family:宋体;"><span>详解</span> <span style="font-family:宋体;">?/span>2</span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >TCP/IP<span style="font-family:宋体;"><span>详解</span> <span style="font-family:宋体;">?/span>3</span></a></p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">数据库：存储数据?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>数据库系l概?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >MySQL 5 <span style="font-family:宋体;"><span>权威指南</span>-(<span style="font-family:宋体;">W?/span>3<span style="font-family:宋体;">?/span>)</span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >MySQL<span style="font-family:宋体;"><span>性能调优与架构设?/span></span></a></p> <p style="margin-left:21.0pt"> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">软g工程Q开发Y件是一个大工程Q需要有一套理论来理软g开发?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>软g工程</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>敏捷软g开?/span></span></a></p> <p> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span><span style="font-family:宋体;">法Q尚未接触?/span></p> <p style="margin-left:21.0pt"> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span>Java<span style="font-family:宋体;">基础Q具体的高语言Q最好的学习地方是</span>java<span style="font-family:宋体;">的官方网站和开源代码?/span> </p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Java JDK6<span style="font-family:宋体;"><span>学习W记</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Effective Java<span style="font-family:宋体;"><span>中文?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Java<span style="font-family:宋体;"><span>~程思想</span> <span style="font-family:宋体;">Q第</span>4<span style="font-family:宋体;">版）</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Java<span style="font-family:宋体;"><span>|络~程</span>(<span style="font-family:宋体;">中文?/span> <span style="font-family: 宋体;">W三?/span>)</span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >JAVA<span style="font-family:宋体;"><span>q发~程实践</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>深入理解</span>Java<span style="font-family:宋体;">虚拟?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Spring in Action<span style="font-family:宋体;"><span>中文?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>深入出</span>Hibernate</span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Struts2<span style="font-family:宋体;"><span>权威指南</span></span></a></p> <p> </p> <p style="margin-left:42.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">ü </span>Java<span style="font-family:宋体;">q阶Q面向对象思想、设计模式和</span>J2EE<span style="font-family:宋体;">深入?/span> </p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >Java<span style="font-family:宋体;"><span>与模?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a ><span style="font-family:宋体;"><span>企业应用架构模式</span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >POJOs IN ACTION<span style="font-family:宋体;"><span>中文?/span></span></a></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><a >J2EE<span style="font-family:宋体;"><span>设计开发编E指?/span></span></a><span style="font-family:宋体;">Q?/span><span>Expert One-on-One J2EE Design and Development</span><span style="font-family:宋体;">Q?/span></p> <p style="margin-left:63.0pt;text-indent:-21.0pt;"><span style="font-family:Wingdings;">n </span><span><a >Expert One-on-One J2EE Development without EJB</a></span></p> <p style="margin-left:42.0pt;text-indent:0cm;"> </p> <p style="margin-left:21.0pt"><span style="font-family:宋体;">学习了这些基之后Q我们在来说分布式，</span>nosql<span style="font-family:宋体;">Q云计算Q企业集成等{。只有掌握了基础我们才能更好的创新?/span></p> </div><img src ="http://www.aygfsteel.com/yangpingyu/aggbug/369530.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/yangpingyu/" target="_blank">yangpingyu</a> 2012-02-07 13:45 <a href="http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369530.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>jvmq行时数据区?/title><link>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369508.html</link><dc:creator>yangpingyu</dc:creator><author>yangpingyu</author><pubDate>Tue, 07 Feb 2012 02:27:00 GMT</pubDate><guid>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369508.html</guid><wfw:comment>http://www.aygfsteel.com/yangpingyu/comments/369508.html</wfw:comment><comments>http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369508.html#Feedback</comments><slash:comments>0</slash:comments><wfw:commentRss>http://www.aygfsteel.com/yangpingyu/comments/commentRss/369508.html</wfw:commentRss><trackback:ping>http://www.aygfsteel.com/yangpingyu/services/trackbacks/369508.html</trackback:ping><description><![CDATA[<div> <p><span style="font-size:12.0pt">Java</span><span style="font-size:12.0pt;font-family:宋体;">语言?/span><span style="font-size:12.0pt">c</span><span style="font-size:12.0pt; font-family:宋体;">语言有一个非帔R要的区别是Q内存管理方式的不同Q?/span><span style="font-size:12.0pt">java</span><span style="font-size:12.0pt; font-family:宋体;">语言内存理不需要程序开发h员关注，?/span><span style="font-size:12.0pt">c</span><span style="font-size:12.0pt; font-family:宋体;">语言的内存的h和释N是开发h员来处理。辩证的思维来看Q不同内存管理实现方式有优点和缺点，所以语a应用的场景，效率会有很大不同?/span></p> <p> </p> <p><span style="font-size:12.0pt">Jvm</span><span style="font-size:12.0pt;font-family:宋体;">q行时的数据区域主要有：E序计数器、虚拟机栈、本地方法栈、方法区和堆。其中程序计数器、虚拟机栈和本地Ҏ(gu)栈是U程独nQ而方法区和堆是所有线E共享?/span></p> <p style="margin-left:21.0pt;text-indent:-21.0pt;"><span style="font-size:12.0pt;font-family:Wingdings;">ü </span><span style="font-size:12.0pt;font-family:宋体;">E序计数器：</span><span style="font-size:12.0pt">jvm</span><span style="font-size:12.0pt; font-family:宋体;">每个U程都有一个程序计数器。在M时刻都有一个线E的Ҏ(gu)在运行，如果q个Ҏ(gu)不是本地Ҏ(gu)Q那么程序计数器存放的就是正在执行的指o地址Q如果是本地Ҏ(gu)Q那么程序计数器中存攄指定地址?/span><span style="font-size:12.0pt">undefined</span><span style="font-size: 12.0pt;font-family:宋体;">?/span></p> <p style="margin-left:21.0pt;text-indent:-21.0pt;"><span style="font-size:12.0pt;font-family:Wingdings;">ü </span><span style="font-size:12.0pt;font-family:宋体;">虚拟机栈Q当</span><span style="font-size:12.0pt">jvm</span><span style="font-size:12.0pt; font-family:宋体;">创徏一个线E的时候就会ؓU程分配一个虚拟机栈。主要用于存放方法的一些本地变量和部分l果Q一般这里的大小都是固定Q但不是l对。一个方法的执行到完成就是栈的入栈和出栈。假讑֜某方法中定义了一个对?/span><span style="font-size:12.0pt">Object obj=new Object();</span><span style="font-size:12.0pt;font-family:宋体;">其中</span><span style="font-size:12.0pt">obj</span><span style="font-size:12.0pt; font-family:宋体;">是存攑֜栈上Q?/span><span style="font-size:12.0pt">new Object()</span><span style="font-size:12.0pt; font-family:宋体;">是在堆上分配?/span><span style="font-size:12.0pt">-Xss</span><span style="font-size:12.0pt;font-family: 宋体;">可以控制</span><span style="font-size: 12.0pt">jvm</span><span style="font-size:12.0pt;font-family:宋体;">虚拟机栈的大?/span></p> <p style="margin-left:21.0pt;text-indent:-21.0pt;"><span style="font-size:12.0pt;font-family:Wingdings;">ü </span><span style="font-size:12.0pt;font-family:宋体;">本地Ҏ(gu)栈：大体跟虚拟机栈类|不过是给本地Ҏ(gu)使用的。虚拟机栈和本地Ҏ(gu)栈在</span><span style="font-size:12.0pt">hotspot</span><span style="font-size:12.0pt; font-family:宋体;">是没有分开实现的，而是l称为栈?/span></p> <p style="margin-left:21.0pt;text-indent:-21.0pt;"><span style="font-size:12.0pt;font-family:Wingdings;">ü </span><span style="font-size:12.0pt;font-family:宋体;">Ҏ(gu)区：主要存放静态变量，帔RQ类加蝲器加载的cȝ一些信息?/span></p> <p style="margin-left:21.0pt;text-indent:-21.0pt;"><span style="font-size:12.0pt;font-family:Wingdings;">ü </span><span style="font-size:12.0pt;font-family:宋体;">堆：</span><span style="font-size:12.0pt">jvm</span><span style="font-size:12.0pt; font-family:宋体;">l大部分的对象分配都在堆上分配?/span><span style="font-size:12.0pt">-Xmn –Xmx</span><span style="font-size: 12.0pt;font-family:宋体;">是控制堆最值和最大|一般堆的大在使用了超q?/span><span style="font-size:12.0pt">mx</span><span style="font-size:12.0pt; font-family:宋体;">讑֮?/span><span style="font-size:12.0pt">70%</span><span style="font-size:12.0pt;font-family: 宋体;">的时候，׃自动扩大到最大|所以防止这U扩大和~小我们讄成一L倹{?/span></p> </div><img src ="http://www.aygfsteel.com/yangpingyu/aggbug/369508.html" width = "1" height = "1" /><br><br><div align=right><a style="text-decoration:none;" href="http://www.aygfsteel.com/yangpingyu/" target="_blank">yangpingyu</a> 2012-02-07 10:27 <a href="http://www.aygfsteel.com/yangpingyu/archive/2012/02/07/369508.html#Feedback" target="_blank" style="text-decoration:none;">发表评论</a></div>]]></description></item><item><title>ClassCastExceptionhttp://www.aygfsteel.com/yangpingyu/archive/2012/01/10/368240.htmlyangpingyuyangpingyuTue, 10 Jan 2012 08:07:00 GMThttp://www.aygfsteel.com/yangpingyu/archive/2012/01/10/368240.htmlhttp://www.aygfsteel.com/yangpingyu/comments/368240.htmlhttp://www.aygfsteel.com/yangpingyu/archive/2012/01/10/368240.html#Feedback0http://www.aygfsteel.com/yangpingyu/comments/commentRss/368240.htmlhttp://www.aygfsteel.com/yangpingyu/services/trackbacks/368240.html
ClassCastExceptioncd转换异常Q是一个运行时异常?/span>
非常常见是不同cd之间的强制类型{换就会抛?/span>ClassCastException异常。还有一U就是不?/span>ClassLoader加蝲的相同的cd转换也会抛出ClassCastException。接下来我用代码来详l解释下?/span>
1?nbsp;强制cd转换
public class ClassCastExceptionTest {
/**
* @param args
*/
public static void main(String[] args) {
Animal a1 = new Dog(); //1
Animal a2 = new Cat(); //2
Dog d1 = (Dog)a1; //3
Dog d2 = (Dog)a2; //4
}
}
把猫转换成狗Q是不对的。后面注释ؓ4的代码是无法正常赋值的?/span>
Exception in thread "main" java.lang.ClassCastException: Cat cannot be cast to Dog
at ClassCastExceptionTest.main(ClassCastExceptionTest.java:13)
2?nbsp;不同classloader加蝲相同cdcM间的转换
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
public class ClassCastExceptionTest {
/**
* @param args
*/
public static void main(String[] args) throws Exception {
File file = new File(Thread.currentThread().getContextClassLoader().getResource("").getPath());
URL[] urls = {file.toURL()};
URLClassLoader classloader1 = new URLClassLoader(urls, ClassLoader.getSystemClassLoader().getParent());
Class classloader1Animal1 = classloader1.loadClass("Dog");
Dog dog1 = (Dog)classloader1Animal1.newInstance();
URLClassLoader classloader2 = new URLClassLoader(urls, ClassLoader.getSystemClassLoader().getParent());
Class classloader1Animal2 = classloader1.loadClass("Dog");
Dog dog2 = (Dog)classloader1Animal1.newInstance();
dog1 = dog2;
}
}
代码中我们看?/span>dog1=dog2Q这栯值是会抛异常的?/span>
Exception in thread "main" java.lang.ClassCastException: Dog cannot be cast to Dog
at ClassCastExceptionTest.main(ClassCastExceptionTest.java:17)
以后大家遇到classCastException的时候要注意了，不一定是强制cd转换D的，也有可能不同?/span>classloader加蝲了相同的c，然后q个cM同的实例q行赋倹{?/span>
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