One 、 Reference link

PHP SimpleXML function -W3school

PHP: SimpleXML - Manual

PHP XML SimpleXML | Novice tutorial

PHP: JSON - Manual

PHP JSON | Novice tutorial

Two 、 Example

Two 、 Code

mysql.xml file

<?xml version="1.0"?>
<mysql>
    <!-- Database name -->
    <database>foxtown</database>
    <!-- Database user name -->
    <username>root</username>
    <!-- Database password -->
    <passwd>toor</passwd>
</mysql>

test1.php file

<?php
    $xml_object = simplexml_load_file("mysql.xml");// Import xml
    $xml_json = json_encode($xml_object);// Convert to json data 
    $xml_array = json_decode($xml_json,true);// Convert to array 
    print_r($xml_array);
    echo "<br>";
    echo $xml_array["username"];// full name 
    echo "<br>";
    echo $xml_array["passwd"];// password 
?>