private Timer timer; 
 
/**
* 简易定时器
* @param delay  多久后开始执行。毫秒
* @param period 执行的间隔时间。毫秒
*/ 
public void test(long delay, long period) { 
        timer = new Timer(); 
        timer.schedule(new TimerTask() { 
            public void run() { 
                //你 的 操作方法 
                System.out.println(System.currentTimeMillis()); 
            } 
        }, delay, period); 
}

package classloader; 
/**
 * @author vma
 */ 
// 自定义一个类加载器 
public class DynamicClassLoader extends ClassLoader { 
    public Class<?> findClass(byte[] b) throws ClassNotFoundException { 
        return defineClass(null, b, 0, b.length); 
    } 

package classloader; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.IOException; 
/**
 * @author vma
 */ 
public class ManageClassLoader { 
    DynamicClassLoader dc =null; 

    Long lastModified = 0l; 
    Class c = null; 
    //加载类， 如果类文件修改过加载，如果没有修改，返回当前的 
    public Class loadClass(String name) throws ClassNotFoundException, IOException{ 
     if (isClassModified(name)){ 
        dc =  new DynamicClassLoader(); 
      return c = dc.findClass(getBytes(name)); 
     } 
     return c; 
    } 
    //判断是否被修改过 
    private boolean isClassModified(String filename) { 
        boolean returnValue = false; 
        File file = new File(filename); 
        if (file.lastModified() > lastModified) { 
            returnValue = true; 
        } 
        return returnValue; 
    } 
       // 从本地读取文件 
       private byte[] getBytes(String filename) throws IOException { 
        File file = new File(filename); 
        long len = file.length(); 
        lastModified = file.lastModified(); 
        byte raw[] = new byte[(int) len]; 
        FileInputStream fin = new FileInputStream(file); 
        int r = fin.read(raw); 
        if (r != len) {
            throw new IOException("Can't read all, " + r + " != " + len);
        }
        fin.close();
        return raw;
    }
}

class Thread1 extends Thread{
  public void run(){
//调用业务方法（查看文件是否改变）
Thread.currentThread().sleep("100000");
}