how to parase XML using PHP

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　　PHP中的几种XML解析方法总结如下：以解析Google API 接口提供的天气情况为例，取天气及气温。API地址：http://www.google.com/ig/api?weather=shanghai
　　【XML文件内容】
  <?xml version="1.0" ?> 
   <xml_api_reply version="1">
             <weather module_id="0" tab_id="0" mobile_row="0" mobile_zipped="1" row="0" section="0">
                   <forecast_information>
                         <city data="Shanghai, Shanghai" />
                         <postal_code data="shanghai" />
                         <latitude_e6 data="" />
                         <longitude_e6 data="" /> 
                         <forecast_date data="2010-07-15" /> 
                         <current_date_time data="2010-07-15 20:00:00 +0000" /> 
                         <unit_system data="US" /> 
                     </forecast_information>
                     <current_conditions>
                          <condition data="Light rain" />
                          <temp_f data="82" /> 
                          <temp_c data="28" /> 
                          <humidity data="Humidity: 84%" />
                          <icon data="/ig/images/weather/mist.gif" /> 
                          <wind_condition data="Wind: SE at 7 mph" /> 
                      </current_conditions>
                      <forecast_conditions>
                          <day_of_week data="Thu" />
                          <low data="75" /> 
                          <high data="91" />
                          <icon data="/ig/images/weather/chance_of_storm.gif" />
                          <condition data="Chance of Storm" />
                      </forecast_conditions>
                      <forecast_conditions>
                           <day_of_week data="Fri" /> 
                           <low data="75" />
                           <high data="89" /> 
                           <icon data="/ig/images/weather/chance_of_storm.gif" /> 
                           <condition data="Chance of Storm" />
                       </forecast_conditions>
                       <forecast_conditions>
                            <day_of_week data="Sat" />
                             <low data="80" />
                             <high data="91" />
                             <icon data="/ig/images/weather/chance_of_storm.gif" />
                             <condition data="Chance of Storm" /> 
                         </forecast_conditions>
                         <forecast_conditions>
                              <day_of_week data="Sun" /> 
                              <low data="82" /> 
                              <high data="95" /> 
                              <icon data="/ig/images/weather/chance_of_storm.gif" />
                              <condition data="Chance of Storm" />
                           </forecast_conditions>
               </weather>
  </xml_api_reply>
　　【使用DomDocument解析】
　　<?PHP
header("Content-type:text/html; Charset=utf-8");
$url = http://www.google.com/ig/api?weather=shanghai;
 
//  加载XML内容
$content = file_get_contents($url);
$content = get_utf8_string($content);
$dom = DOMDocument::loadXML($content);
/*
此处也可使用如下所示的代码，
$dom = new DOMDocument();
$dom->load($url);
 */
 
$elements = $dom->getElementsByTagName("current_conditions");
$element = $elements->item(0);
$condition = get_google_xml_data($element, "condition");
$temp_c = get_google_xml_data($element, "temp_c");
echo '天气：', $condition, '<br />';
echo '温度：', $temp_c, '<br />';
 
function get_utf8_string($content) {    //  将一些字符转化成utf8格式
    $encoding = mb_detect_encoding($content, array('ASCII','UTF-8','GB2312','GBK','BIG5'));
    return  mb_convert_encoding($content, 'utf-8', $encoding);
}
 
function get_google_xml_data($element, $tagname) {
    $tags = $element->getElementsByTagName($tagname);   //  取得所有的$tagname
    if ($items->length > 1) {
        return $items;
    }
    $tag = $tags->item(0);  //  获取第一个以$tagname命名的标签
    if ($tag->hasAttributes()) {    //  获取data属性
        $attribute = $tag->getAttribute("data");
        return $attribute;
    }else {
        return false;
    }
}
?>
　　这只是一个简单的示例，仅包括了loadXML, item, getAttribute,getElementsByTagName等方法，还有一些有用的方法，这个依据你的实际需要。
　　【XMLReader】
当我们要用php解读xml的内容时，有很多物件提供函式，让我们不用一个一个字元去解析，而只要根据标签和属性名称，就能取出文件中的属性与内容了，相较之下方便许多。其中XMLReader循序地浏览过xml档案的节点，可以想像成游标走过整份文件的节点，并抓取需要的内容。
　　
 <?PHP
header("Content-type:text/html; Charset=utf-8");
$url = http://www.google.com/ig/api?weather=shanghai;
 
//  加载XML内容
$xml = new XMLReader();
$xml->open($url);
 
$condition = '';
$temp_c = '';
while ($xml->read()) {
//      echo $xml->name, "==>", $xml->depth, "<br>";
      if (!empty($condition) && !empty($temp_c)) {
          break;
      }
      if ($xml->name == 'condition' && empty($condition)) {  //  取第一个condition
            $condition = $xml->getAttribute('data');
      }
 
      if ($xml->name == 'temp_c' && empty($temp_c)) {    //  取第一个temp_c
          $temp_c = $xml->getAttribute('data');
      }
 
      $xml->read();
}
 
$xml->close();
echo '天气：', $condition, '<br />';
echo '温度：', $temp_c, '<br />';
　　我们只是需要取第一个condition和第一个temp_c,于是遍历所有的节点，将遇到的第一个condition和第一个temp_c写入变量，最后输出。
　　【DOMXPath】
这种方法需要使用DOMDocument对象创建整个文档的结构，
　　<?PHP
header("Content-type:text/html; Charset=utf-8");
$url = http://www.google.com/ig/api?weather=shanghai;
 
//  加载XML内容
$dom = new DOMDocument();
$dom->load($url);
 
$xpath = new DOMXPath($dom);
$element = $xpath->query("/xml_api_reply/weather/current_conditions")->item(0);
$condition = get_google_xml_data($element, "condition");
$temp_c = get_google_xml_data($element, "temp_c");
echo '天气：', $condition, '<br />';
echo '温度：', $temp_c, '<br />';
 
function get_google_xml_data($element, $tagname) {
    $tags = $element->getElementsByTagName($tagname);   //  取得所有的$tagname
    if ($items->length > 1) {
        return $items;
    }
    $tag = $tags->item(0);  //  获取第一个以$tagname命名的标签
    if ($tag->hasAttributes()) {    //  获取data属性
        $attribute = $tag->getAttribute("data");
        return $attribute;
    }else {
        return false;
    }
}
?>
　　【xml_parse_into_struct】
说明：int xml_parse_into_struct ( resource parser, string data, array &values [, array &index] )
　　该函数将 XML 文件解析到两个对应的数组中，index 参数含有指向 values 数组中对应值的指针。最后两个数组参数可由指针传递给函数。
注意: xml_parse_into_struct() 失败返回 0，成功返回 1。这和 FALSE 与 TRUE 不同，使用例如 === 的运算符时要注意。
　　<?PHP
header("Content-type:text/html; Charset=utf-8");
$url = http://www.google.com/ig/api?weather=shanghai;
 
//  加载XML内容
$content = file_get_contents($url);
$p = xml_parser_create();
xml_parse_into_struct($p, $content, $vals, $index);
xml_parser_free($p);
 
echo '天气：', $vals[$index['CONDITION'][0]]['attributes']['DATA'], '<br />';
echo '温度：', $vals[$index['TEMP_C'][0]]['attributes']['DATA'], '<br />'; 
 
【Simplexml】
此方法在PHP5中可用
这个在google的官方文档中有相关的例子，如下：
 
// 城市，用城市拼音
$city = empty($_GET['city']) ? 'shanghai' : $_GET['city'];
$content = file_get_contents("http://www.google.com/ig/api?weather=$city&hl=zh-cn");
$content || die("No such city's data");
$content = mb_convert_encoding($content, 'UTF-8', 'GBK');
$xml = simplexml_load_string($content);
 
$date = $xml->weather->forecast_information->forecast_date->attributes();
$html = $date. "<br>\r\n";
 
$current = $xml->weather->current_conditions;
 
$condition = $current->condition->attributes();
$temp_c = $current->temp_c->attributes();
$humidity = $current->humidity->attributes();
$icon = $current->icon->attributes();
$wind = $current->wind_condition->attributes();
 
$condition && $condition = $xml->weather->forecast_conditions->condition->attributes();
$icon && $icon = $xml->weather->forecast_conditions->icon->attributes();
 
$html.= "当前: {$condition}, {$temp_c}°C,<img src='http://www.google.com/ig{$icon}'/> {$humidity} {$wind} <br />\r\n";
 
foreach($xml->weather->forecast_conditions as $forecast) {
    $low = $forecast->low->attributes();
    $high = $forecast->high->attributes();
    $icon = $forecast->icon->attributes();
    $condition = $forecast->condition->attributes();
    $day_of_week = $forecast->day_of_week->attributes();
    $html.= "{$day_of_week} : {$high} / {$low} °C, {$condition} <img src='http://www.google.com/ig{$icon}' /><br />\r\n";
}
 
header('Content-type: text/html; Charset: utf-8');
print $html;
?>