code: @Override
  	protected Class<?> loadClass(String className, boolean resolve) throws ClassNotFoundException {
  		Class<?> clazz= null;
  		try {
  			clazz = findClass(className);//查找已经加载过的类或者待加载的类
  		} catch (Exception e) {
  		}
  		if (clazz == null) {// 系统类加载
  			try {
  				clazz = findSystemClass(className);
  			} catch (ClassNotFoundException e) {
  			}
  		}
  		if (clazz == null) {// 上层加载器加载
  			ClassLoader parent=getParent();
  			if(parent!=null)
  			{
  				try {
  					clazz = parent.loadClass(className);
  				} catch (Exception e) {
  				}
  			}
  		}
  		// 查找当前类加载中已加载的
  		if (clazz == null) {
  			throw new ClassNotFoundException("className:"+className+",resolve:"+resolve);
  		}
  		String classLoader = "" + clazz.getClassLoader();
  		if (resolve) {// 解析类结构
  			resolveClass(clazz);
  		}
  		log.trace("loadClass " + (clazz == null) + ":" + className + ",resolve=" + resolve + ",Clazz=" + clazz+ ",ClassLoader=" + classLoader);
  		return clazz;
  	}
docs: 加载类,如果是系统类则交给系统加载 如果当前类已经加载则返回类 如果当前类没有加载则定义并返回