Java XPath API - 获取表示子树的字符串

Question

我的问题不是关于 xpath 语法，它与围绕 xpath 的 java API 有关。考虑以下 xml:

<wrapper>
    <metadata>
        <somefield>somevalue</somefield>
        <anotherfield>othervalue</anotherfield>
    </metadata>
    <data>
        <some>
            <unique>
                <xml>
                    <structure>stuff</structure>
                </xml>
            </unique>
        </some>
    </data>
</wrapper>

我可以使用以下代码使用 xpath 轻松获取元数据字段:

 XPath xp = XPathFactory.newInstance().newXPath();
 Node node = (Node) xp.evaluate("/wrapper/metadata/somefield", xmlDoc, XPathConstants.NODE);
 String somefield = node.getFirstChild().getNodeValue();

我正在为如何获得一个代表 xml 的 subtree 的字符串而苦苦挣扎，该字符串以 <some> 开头标签。换句话说，我要写什么代码来获得一个字符串，当打印出来时，会打印出以下内容？ xpath 查询将是“/wrapper/data/some”，但我不知道如何适本地使用 xpath api。

<some>
    <unique>
        <xml>
            <structure>stuff</structure>
        </xml>
    </unique>
</some>

Answer 1

您只需使用 Transformer 将从 XPathExpression 返回的 Node 转换为 String就像您将文档写入文件一样，这里是一个完整的示例:

public static void main(String[] args) throws Exception {
    final String xml = "<wrapper>\n"
            + "    <metadata>\n"
            + "        <somefield>somevalue</somefield>\n"
            + "        <anotherfield>othervalue</anotherfield>\n"
            + "    </metadata>\n"
            + "    <data>\n"
            + "        <some>\n"
            + "            <unique>\n"
            + "                <xml>\n"
            + "                    <structure>stuff</structure>\n"
            + "                </xml>\n"
            + "            </unique>\n"
            + "        </some>\n"
            + "    </data>\n"
            + "</wrapper>";
    final Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(new ByteArrayInputStream(xml.getBytes(Charsets.UTF_8)));
    final XPathExpression xpath = XPathFactory.newInstance().newXPath().compile("//some");
    final Node node = (Node) xpath.evaluate(doc, XPathConstants.NODE);
    StringWriter sw = new StringWriter();
    TransformerFactory tf = TransformerFactory.newInstance();
    Transformer transformer = tf.newTransformer();
    transformer.setOutputProperty(OutputKeys.METHOD, "xml");
    transformer.setOutputProperty(OutputKeys.INDENT, "yes");
    transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
    transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
    transformer.transform(new DOMSource(node), new StreamResult(sw));
    System.out.println(sw.toString());
}