PHP での try catch の使用

<?php
class Oss {
    public static function connect() {
    	throw new Exception("oss connect error");
    	return &#39;oss object&#39;;
    }
}
//调用三层
class S3{
	public static function connect() {
		//throw new Exception("s3 connect error");
    	return &#39;s3 object&#39;;
    }
}
//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(&#39;Oss&#39;,"http://xxxx");
	} catch (Exception $e1) {
		$conn=callReader(&#39;S3&#39;,"http://xxxx");
	}
	return $conn;
}
//最先的入口
try{
	var_dump(getMessage());
}catch(Exception $e){}