Ajax帖子在服务器上有空值

I'm trying to save an image file out of a base64 string received from the client side.

So I have this ajax post:

 $.ajax({type: "POST", url: "upload_post.php", data: postData, dataType: "text", success: function(result){
        alert("post result: " + result + " - data:" + postData);
        location.reload();
    }});

Here is an example of postData (which I know contains data):

{"ship_id":"407","base64_upload":"ABCSFSAFGDGFA....."}

Now here is a my php code that handles this post:

$id = $_POST['ship_id'];
$img = $_POST['base64_upload'];
define('UPLOAD_DIR', 'news.site.com/docs/'.$id.'/');
$img = str_replace('data:image/png;base64,', '', $img);
$img = str_replace(' ', '+', $img);
$data = base64_decode($img);
$file = UPLOAD_DIR . uniqid() . '.png';
$success = file_put_contents($file, $data);
print $success ? $file : 'Unable to save the file. '.$file.'';

The problem is the $_POST variables are always empty. why is that? json related? location.reload() related? and how do I fix it?

EDIT

I have got these variables posted with actual data by doing JSON.parse(postData) on the ajax data. Now my problem is I still can't save the image file. any help?

Once again, I'm answering my own question. The problem was I have define('UPLOAD_DIR', 'news.site.com/docs/'.$id.'/'); and then $file = UPLOAD_DIR . uniqid() . '.png'; and this UPLOAD_DIR directory doesn't really exists. So I added a check if it exists and then created the directory before creating the file:

$id = $_POST['ship_id'];
$img = $_POST['base64_upload'];
define('UPLOAD_DIR', 'news.site.com/docs/'.$id.'/');
$file2 = UPLOAD_DIR;
if(!file_exists($file2)){
    mkdir($file2, 0777, true);
    $img = str_replace('data:image/png;base64,', '', $img);
    $img = str_replace(' ', '+', $img);
    $data = base64_decode($img);
    $file = UPLOAD_DIR . uniqid() . '.png';
    $success = file_put_contents($file, $data);
    print $success ? $file : 'Unable to save the file. '.$file.'';
}

This is what I do for jQuery Post. I hope it helps you

$.post("upload_post.php",
{
    ship_id: "407",
    base64_upload: "ABCSFSAFGDGFA....."
},
function(data, status){
    alert("post result: " + status+ " - data:" + data);
    location.reload();
});

You fetch the data in php exactly the same.