URL能够正常的访问
使用的是微信公众平台给出的文档。

<?php
/**
  * wechat php test
  */

//define your token
define("TOKEN", "weixin");
$wechatObj = new wechatCallbackapiTest();

if($_GET[echostr]){

$wechatObj->valid();
    
}else {
    
}

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;
        }
    }
}

?>

改动位置就在最前面加入了一个if 判断，后面没有做任何的修改

google了方法也试了没有解决，所有在这里发帖了，谢谢各位。