[jQuery] jQuery, ajax, json, php

[David .Wu]

If I send a json format to php, how to get the value from php? for
example

front page
<script>
var jsonStr = '{"name": "David", "age", "23"}';
$.ajax({
        url: 'json.php',
        type: 'POST',
        cache: false,
        data: {json: jsonStr},
        success: function(data) {
                alert(data);
        }
});
</script>

php page
<?php
$json = $_POST['json'];

// it's get {"name":"David","age": "23"}, but how to gete name?
?>