jvm 内存监控2

引用：http://www.189works.com/article-75562-1.html

一个类对JVM可用内存进行了监测

import java.util.Timer;
import java.util.TimerTask;
import java.util.Calendar;
import java.util.GregorianCalendar;
/**
Title:GCTimerTask
* @author zhuangyan
* @msn:nacl_zhuang@hotmail.com
* @qq:368924454
* @version 1.0
*/
public class GCTimerTask
extends TimerTask {
private static GCTimerTask instance = null;
public void run() {
Calendar cal = new GregorianCalendar();
int hour24 = cal.get(Calendar.HOUR_OF_DAY); // 0..23
int min = cal.get(Calendar.MINUTE); // 0..59
System.out.print("["+String.valueOf(hour24)+":"+String.valueOf(min)+"]");
System.out.println("JVM可用内存:" + java.lang.Runtime.getRuntime().
freeMemory() / (1024*1024)+"M/"+java.lang.Runtime.getRuntime().totalMemory()/(1024*1024)+"M" );
System.gc();
}
private void startWork()
{
Timer t = new Timer();
t.schedule(instance,0,1000*60);
}
public static GCTimerTask getInstance()
{
if(instance==null) {
instance = new GCTimerTask();
instance.startWork();
}
return instance;
}
}

这个类虽然简单,但初学者从中应该学到
1)timer类的用法
2)java.lang.Runtime.getRuntime().freeMemory(),java.lang.Runtime.getRuntime().totalMemory(),System.gc()
这三个方法的使用,需要说明的是System.gc()并不能**JVM马上释放内存,如果那样,我的内存溢出问题早就解决了.
3)getInstance()单例模式,
4)最后的就是怎么用这个类的问题,我把它放到了EncodingFilter类中,现在很多JSP程序中都有这个类吧

public final void init(final FilterConfig arg0) throws ServletException {
GCTimerTask.getInstance();
this.filterConfig = arg0;
this.encoding = filterConfig.getInitParameter("encoding");
String value = filterConfig.getInitParameter("ignore");
if (value == null) {
this.ignore = true;
}
else if (value.equalsIgnoreCase("true")) {
this.ignore = true;
}
else if (value.equalsIgnoreCase("yes")) {
this.ignore = true;
}
else {
this.ignore = false;
}
}

JVM可用内存:405M/508M