微信公众平台实现获取用户OpenID的方法

<?php 
if(isset($_SESSION['user'])){ 
 print_r($_SESSION['user']);
exit;
}
$APPID='公众号在微信的appid';
$REDIRECT_URI='https://www.jb51.net/callback.php';
$scope='snsapi_base';
//$scope='snsapi_userinfo';//需要授权
$url='https://open.weixin.qq.com/connect/oauth2/authorize?appid='.$APPID.'&redirect_uri='.urlencode($REDIRECT_URI).'&response_type=code&scope='.$scope.'&state='.$state.'#wechat_redirect';
header("Location:".$url);
?>

<?php
//https://www.jb51.net/callback.php
$appid = "公众号在微信的appid"; 
$secret = "公众号在微信的app secret"; 
$code = $_GET["code"]; 
$get_token_url = 'https://api.weixin.qq.com/sns/oauth2/access_token?appid='.$appid.'&secret='.$secret.'&code='.$code.'&grant_type=authorization_code';
$ch = curl_init();
curl_setopt($ch,CURLOPT_URL,$get_token_url); 
curl_setopt($ch,CURLOPT_HEADER,0); 
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1 ); 
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10); 
$res = curl_exec($ch); 
curl_close($ch); 
$json_obj = json_decode($res,true); 
//根据openid和access_token查询用户信息 
$access_token = $json_obj['access_token']; 
$openid = $json_obj['openid']; 
$get_user_info_url = 'https://api.weixin.qq.com/sns/userinfo?access_token='.$access_token.'&openid='.$openid.'&lang=zh_CN'; 

$ch = curl_init(); 
curl_setopt($ch,CURLOPT_URL,$get_user_info_url); 
curl_setopt($ch,CURLOPT_HEADER,0); 
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1 ); 
curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10); 
$res = curl_exec($ch); 
curl_close($ch); 

//解析json 
$user_obj = json_decode($res,true); 
$_SESSION['user'] = $user_obj; 
print_r($user_obj); 
?>