define("TOKEN","myToken");// 后台填写的token，在微信公众平台启用
$wechatObj = new wechatAPI();
$wechatObj->isValid();
class wechatAPI
{
  public function isValid()//验证微信接口，验证函数以外的代码和微信公众号开发token设置相同
  {
     $echoStr = $_GET["echostr"];
     if ($this->checkSignature()) {
       header('content-type:text');//add，一定要加入header
      echo $echoStr;
      exit;
     }
  }
  private function checkSignature()  //官方的验证函数
  {
     $signature = $_GET["signature"];
     $timestamp = $_GET["timestamp"];
     $nonce = $_GET["nonce"];
     $token = TOKEN;
     $tmpArr = array($token, $timestamp, $nonce);
     sort($tmpArr, SORT_STRING);
     $tmpStr = implode( $tmpArr );
     $tmpStr = sha1( $tmpStr );
     if( $tmpStr == $signature ){
      return true;
     }else{
      return false;
     }
  }
};