php如何获取json数据？

//页面1.模拟请求的json数据header("Content-type: text/html; charset=utf-8");//模拟post 请求function acquireInfoByPost($_url, $_json){    $ch = curl_init();    curl_setopt($ch, CURLOPT_POST, 1);    curl_setopt($ch, CURLOPT_URL, $_url);    curl_setopt($ch, CURLOPT_POSTFIELDS, $_json);    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);    curl_setopt($ch, CURLOPT_HTTPHEADER, array(            'Content-Type: application/json; charset=utf-8',            'Content-Length: ' . strlen($_json)        )    );    $result = curl_exec($ch);    $httpCode = curl_getinfo($ch, CURLINFO_HTTP_CODE);    $stateArr=array('result'=>$result,'httpCode'=>$httpCode);    return $stateArr;}$url = "http://IP/api/?controller=showHealthRecords";$json = '{"user_id":"1","user_name":"jack"}';//json格式格式的数据$res = acquireInfoByPost($url,$json);print_r($res['result']);//页面2.获取请求的json数据$info = file_get_contents("php://input");echo $info;die();//页面1打印的结果是：{"user_id":"1","user_name":"jack"};//结果与请求的json数据一致