code: public static Object tryInstance(String clsName,ClassLoader loader)
  	{
  		try
  		{
  			return instance(clsName,loader);
  		}
  		catch (Exception ex)
  		{
  			return null;
  		}
  	}
docs: 实例化一个类，如果不成功，返回null
  @param clsName
  @return