<?php

class Oss {

    public static function connect() {

    	throw new Exception("oss connect error");

    	return 'oss object';

    }

}

//调用三层

class S3{

	public static function connect() {

		//throw new Exception("s3 connect error");

    	return 's3 object';

    }

}

//调用二层

function callReader($class,$url){

	try{

		$conn=call_user_func_array(array($class, "connect"),array());

		return $conn;

	}catch(Exception $e){

		throw $e;

	}finally{

		//无论如何都会执行,在这记录日志

	}

}

//调用一层

function getMessage(){

	$conn=null;

	try {

	    $conn=callReader('Oss',"http://xxxx");

	} catch (Exception $e1) {

		$conn=callReader('S3',"http://xxxx");

	}

	return $conn;

}

//最先的入口

try{

	var_dump(getMessage());

}catch(Exception $e){}