对于URLClassLoader，Eclipse执行正确，而命令行执行抛出异常

Question

【0】问题描述
0.1）晚辈我想利用URLClassLoader 加载某目录下的class文件，执行结果发现，Eclipse执行正确，而命令行却抛出异常ClassNotFoundException，求各位前辈帮帮忙。。谢谢。

 package com.tomcat.classloader;

import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;

public class URLClassLoaderTest {

    public final static String dir = System.getProperty("user.dir") + 
            File.separator + "webroot" + File.separator;

    public static void main(String[] args) {
        URL u;
        try {
            File file = new File(dir);
            URL url = file.toURI().toURL();
            URL[] urls = new URL[]{url};
            URLClassLoader loader = new URLClassLoader(urls);  

            Class<?> beanClass = loader.loadClass("servlet.Bean");
            System.out.println("hello, class loader.");
        } catch (Exception e) {
            e.printStackTrace();
        }  
    }
}

 public class Bean {

    public void sayHello() {
        System.out.println("Hello from loaded Bean class for servlet package!!!");
    }

    public static void main(String[] args) {
        System.out.println("i am a bean!");
    }
}