从XML文档Java接收子节点

Question

I'm new to xml parsing, but i have to get XML from a specific URL and then save only one resource from it.

How i get xml:

public Document getXMLFile(String urlToXml) {
    try {
        URL url = new URL(urlToXml);
        DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
        DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
        Document document = documentBuilder.parse(url.openStream());
        return document;
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (ParserConfigurationException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } catch (SAXException e) {
        e.printStackTrace();
    }
    return null;
}

This works flawlessly and returns kinda this one document:

<CRates xmlns="****" xmlns:dc="http://purl.org/dc/elements/1.1/"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="******">
    <Date>20161003</Date>
    <Currencies>
        <Currency>
            <ID>AUD</ID>
            <Rate>1.46380</Rate>
        </Currency>
        <Currency>
            <ID>BGN</ID>
            <Rate>1.95580</Rate>
        </Currency>
        <Currency>
            <ID>BRL</ID>
            <Rate>3.64090</Rate>
        </Currency>
        <Currency>
            <ID>CAD</ID>
            <Rate>1.47020</Rate>
        </Currency>
        <Currency>
            <ID>CHF</ID>
            <Rate>1.09180</Rate>
        </Currency>
        <Currency>
            <ID>CNY</ID>
            <Rate>7.49620</Rate>
        </Currency>
        <Currency>
            <ID>CZK</ID>
            <Rate>27.02100</Rate>
        </Currency>
        <Currency>
            <ID>DKK</ID>
            <Rate>7.44630</Rate>
        </Currency>
        <Currency>
            <ID>GBP</ID>
            <Rate>0.87318</Rate>
        </Currency>
        <Currency>
            <ID>HKD</ID>
            <Rate>8.71450</Rate>
        </Currency>
        <Currency>
            <ID>HRK</ID>
            <Rate>7.50530</Rate>
        </Currency>
        <Currency>
            <ID>HUF</ID>
            <Rate>308.18000</Rate>
        </Currency>
        <Currency>
            <ID>IDR</ID>
            <Rate>14587.14000</Rate>
        </Currency>
        <Currency>
            <ID>ILS</ID>
            <Rate>4.22280</Rate>
        </Currency>
        <Currency>
            <ID>INR</ID>
            <Rate>74.76600</Rate>
        </Currency>
        <Currency>
            <ID>JPY</ID>
            <Rate>113.90000</Rate>
        </Currency>
        <Currency>
            <ID>KRW</ID>
            <Rate>1237.21000</Rate>
        </Currency>
        <Currency>
            <ID>MXN</ID>
            <Rate>21.61500</Rate>
        </Currency>
        <Currency>
            <ID>MYR</ID>
            <Rate>4.62720</Rate>
        </Currency>
        <Currency>
            <ID>NOK</ID>
            <Rate>8.96250</Rate>
        </Currency>
        <Currency>
            <ID>NZD</ID>
            <Rate>1.54540</Rate>
        </Currency>
        <Currency>
            <ID>PHP</ID>
            <Rate>54.17900</Rate>
        </Currency>
        <Currency>
            <ID>PLN</ID>
            <Rate>4.29330</Rate>
        </Currency>
        <Currency>
            <ID>RON</ID>
            <Rate>4.45050</Rate>
        </Currency>
        <Currency>
            <ID>RUB</ID>
            <Rate>70.00100</Rate>
        </Currency>
        <Currency>
            <ID>SEK</ID>
            <Rate>9.59300</Rate>
        </Currency>
        <Currency>
            <ID>SGD</ID>
            <Rate>1.53260</Rate>
        </Currency>
        <Currency>
            <ID>THB</ID>
            <Rate>38.91000</Rate>
        </Currency>
        <Currency>
            <ID>TRY</ID>
            <Rate>3.38610</Rate>
        </Currency>
        <Currency>
            <ID>USD</ID>
            <Rate>1.12360</Rate>
        </Currency>
        <Currency>
            <ID>ZAR</ID>
            <Rate>15.26410</Rate>
        </Currency>
    </Currencies>
</CRates>

The question is - how could i get only one specified node (for example USD) from all this stuff and save it as new xml?

Example for output xml:

<CRates>
    <Date>20160321</Date>
    <ID>USD</ID>
    <Rate>1.12360</Rate>
    </Currency>
</CRates>

Thanks for help,

Cheers

Answer 1

One way could be to use XPaths to match the required node(s).

import javax.xml.xpath.*;

...

XPathFactory xpathFactory = XPathFactory.newInstance();
XPath xpath = xpathFactory.newXPath();
NodeList nodes = (NodeList) xpath.evaluate("//*[@id='USD']", document, XPathConstants.NODESET);

If you're sure there is only one node you're looking for, XPath.evaluate can also return single Element objects, but this version with NodeLists will be able to handle scenarios where multiple nodes are returned.