php如何将xml转为json格式？3种方法分享

$xml = '<root><name>John Doe</name><age>25</age><city>New York</city></root>';
$simpleXML = simplexml_load_string($xml);
$json = json_encode($simpleXML);
echo $json;

$xml = '<root><name>John Doe</name><age>25</age><city>New York</city></root>';
$dom = new DOMDocument;
$dom->loadXML($xml);
$json = json_encode(domDocumentToArray($dom));
echo $json;

function domDocumentToArray($node) {
    $output = array();

    switch ($node->nodeType) {
        case XML_CDATA_SECTION_NODE:
        case XML_TEXT_NODE:
            $output = trim($node->textContent);
            break;

        case XML_ELEMENT_NODE:
            for ($i = 0, $m = $node->childNodes->length; $i < $m; $i++) {
                $child = $node->childNodes->item($i);
                $v = domDocumentToArray($child);
                if(isset($child->tagName)) {
                    $t = $child->tagName;
                    if(!isset($output[$t])) {
                        $output[$t] = array();
                    }
                    $output[$t][] = $v;
                }
                elseif($v) {
                    $output = (string) $v;
                }
            }
            if($node->attributes->length && !is_array($output)) { 
                $output = array('@content'=>$output); 
            }
            if(is_array($output)) {
                if($node->attributes->length) {
                    $a = array();
                    foreach($node->attributes as $attrName => $attrNode) {
                        $a[$attrName] = (string) $attrNode->value;
                    }
                    $output['@attributes'] = $a;
                }
                foreach ($output as $t => $v) {
                    if(is_array($v) && count($v)==1 && $t!='@attributes') {
                        $output[$t] = $v[0];
                    }
                }
            }
            break;
    }
    return $output;
}

$xml = '<root><name>John Doe</name><age>25</age><city>New York</city></root>';
$parser = xml_parser_create();
xml_parse_into_struct($parser, $xml, $values, $tags);
xml_parser_free($parser);
$json = json_encode(XmlToJson::toArray($values));
echo $json;

{
   "root": {
      "name": "John Doe",
      "age": "25",
      "city": "New York"
   }
}