code: public static void checkClassExists(String className, String msg) {
  		try {
  			getDefaultClassLoader().loadClass(className);
  		} catch (ClassNotFoundException e) {
  			throw new WatcherDependencyNotFoundException(msg);
  		}
  	}
docs: 检查依赖是否存在
  @param className 类名
  @param msg 依赖名称