java - 如何解析嵌套的 XML 数据并仅从中提取用户标识？

Question

我有下面的 xml 布局，我想从中提取 <key> </key> 内的所有“userid”值并将它们加载到 HashSet在Java中

<?xml version="1.0" encoding="UTF-8"?>
<response>
   <plds>
      <fld>consumerid</fld>
      <fld>last_set</fld>
   </plds>
   <record>
      <data>934463448   1417753752</data>
      <key_data>
         <key>
            <name>userid</name>
            <value>934463448</value>
         </key>
      </key_data>
   </record>
   <record>
      <data>1228059948  1417753799</data>
      <key_data>
         <key>
            <name>userid</name>
            <value>1228059948</value>
         </key>
      </key_data>
   </record>
</response>

我将从 url 获取以上 xml 数据，并且有可能获取大 XML 文件。解析上述 XML 并提取所有“userid”并将其加载到 Java 的 HashSet 中的最佳方法是什么？

这就是我的开始-

public static Set<String> getUserList(String host, String count) {

    Set<String> usrlist = new HashSet<String>();
    String url = "urlA"; // this url will return me above XML data
    InputStream is = new URL(url).openStream();
    BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));

    // not sure what I should do here which can
    // parse my above xml and extract all the
    // userid and load it into usrlist hash set

    return usrlist;
}

更新:-

这是我试过的-

public static Set<String> getUserList() {

    Set<String> usrlist = new HashSet<String>();
    String url = "urlA"; // this url will return me above XML data
    InputStream is = new URL(url).openStream();
    BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));

    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(new URL(url).openStream());

    XPathFactory xPathfactory = XPathFactory.newInstance();
    XPath xpath = xPathfactory.newXPath();
    XPathExpression expr = xpath.compile("//record/key_data/key[name='userid']/value");
    NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
    for (int i = 0; i < nodes.getLength(); i++) {
        usrlist.add(nodes.item(i).getNodeValue());
    }

    return usrlist;
}

但我在 usrlist 中没有得到任何用户 ID目的？我在这里做错什么了吗？

Answer 1

StAX 是解析大型 xml 的有效方法

    XMLStreamReader r = XMLInputFactory.newInstance().createXMLStreamReader(is);
    while(r.hasNext()) {
        if (r.next() == XMLStreamReader.START_ELEMENT && r.getLocalName().equals("value")) {
            String value = r.getElementText();
            System.out.println(value);
        }
    }