用PHP做微信开发用微信示例代码但是收不到xml表单

<?php/**  * wechat php test  *///define your tokendefine("token", "weixin");$wechatobj = new wechatcallbackapitest();//$wechatobj->valid(); $wechatobj->responsemsg();class wechatcallbackapitest{	public function valid()    {        $echostr = $_get["echostr"];        //valid signature , option        if($this->checksignature()){        	echo $echostr;        	exit;        }    }    public function responsemsg()    {		//get post data, may be due to the different environments		$poststr = $globals["http_raw_post_data"];      	//extract post data		if (!empty($poststr)){                /* libxml_disable_entity_loader is to prevent xml external entity injection,                   the best way is to check the validity of xml by yourself */                libxml_disable_entity_loader(true);              	$postobj = simplexml_load_string($poststr, 'simplexmlelement', libxml_nocdata);                $fromusername = $postobj->fromusername;                $tousername = $postobj->tousername;                $keyword = trim($postobj->content);                $time = time();                $texttpl = "<xml>							<tousername><![cdata[%s]]></tousername>							<fromusername><![cdata[%s]]></fromusername>							<createtime>%s</createtime>							<msgtype><![cdata[%s]]></msgtype>							<content><![cdata[%s]]></content>							<funcflag>0</funcflag>							</xml>";             				if(!empty( $keyword ))                {              		$msgtype = "text";                	$contentstr = "welcome to wechat world!";                	$resultstr = sprintf($texttpl, $fromusername, $tousername, $time, $msgtype, $contentstr);                	echo $resultstr;                }else{                	echo "input something...";                }        }else {        	echo "";        	exit;        }    }			private function checksignature()	{        // you must define token by yourself        if (!defined("token")) {            throw new exception('token is not defined!');        }                $signature = $_get["signature"];        $timestamp = $_get["timestamp"];        $nonce = $_get["nonce"];        				$token = token;		$tmparr = array($token, $timestamp, $nonce);        // use sort_string rule		sort($tmparr, sort_string);		$tmpstr = implode( $tmparr );		$tmpstr = sha1( $tmpstr );				if( $tmpstr == $signature ){			return true;		}else{			return false;		}	}}?>