为什么java中的getElementsByTagNameNS为空? [英] Why is the getElementsByTagNameNS empty in java?

问题描述

我想从 tag2 中获取值，我得到了一个 xml:

I want to get the value out tag2 and I got this a xml:

String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>" +
            "<ns1:schema xmlns:ns1='http://example.com'>" +
                "<ns1:tag1>" +
                "    <ns1:tag2>value</ns1:tag2>" +
                "</ns1:tag1>" +
            "</ns1:schema>"; 

然后解析成文档，想通过tagnameNS获取元素.但是当我运行这个时，节点列表是空的，为什么?

Then parse it to a document and want to get the elements by tagnameNS. But when I run this the nodelist is empty why?

DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        docBuilderFactory.setNamespaceAware(true);
        DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
        Document doc = docBuilder.parse(new InputSource(new StringReader(xml))); 

        NodeList nl = doc.getElementsByTagNameNS("http://example.com", "tag2");

        String a = nl.item(0).getNodeValue();

仍然不能使用 URI.

Still doesnt work with the URI.

推荐答案

getElementsByTagNameNS 正在返回结果.问题是您当前调用了错误的方法来从结果元素中获取文本内容.您需要调用 getTextContext() 而不是 getNodeValue()

getElementsByTagNameNS is returing a result. The issue is that you're currently calling the wrong method to get the text content off the result elements. You need to call getTextContext() and not getNodeValue()

String a = nl.item(0).getTextContent();

DomDemo

下面是一个完整的代码示例.

Below is a complete code example.

package forum13166195;

import java.io.StringReader;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import org.xml.sax.InputSource;

public class DomDemo {

    public static void main(String[] args) throws Exception{
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
                   + "<ns1:schema xmlns:ns1='http://example.com'>"
                       + "<ns1:tag1>"
                           + "<ns1:tag2>value</ns1:tag2>"
                       + "</ns1:tag1>"
                   + "</ns1:schema>";

        DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
        docBuilderFactory.setNamespaceAware(true);
        DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
        Document doc = docBuilder.parse(new InputSource(new StringReader(xml))); 

        NodeList nl = doc.getElementsByTagNameNS("http://example.com", "tag2");

        String a = nl.item(0).getTextContent();
        System.out.println(a);
    }

}

输出

value

<小时>

替代方法

您还可以使用 javax.xml.xpath API(包含在 Java SE 5 及更高版本中)从 XML 文档查询值.这些 API 提供了比 getElementsByTagNameNS 更多的控制.

You can also use the javax.xml.xpath APIs (included in Java SE 5 and above) to query a value from an XML document. These APIs offer a lot more control than getElementsByTagNameNS.

XPathDemo

package forum13166195;

import java.io.StringReader;
import java.util.Iterator;
import javax.xml.namespace.NamespaceContext;
import javax.xml.xpath.*;

import org.xml.sax.InputSource;

public class XPathDemo {

    public static void main(String[] args) throws Exception{
        String xml = "<?xml version=\"1.0\" encoding=\"UTF-8\"?>"
                   + "<ns1:schema xmlns:ns1='http://example.com'>"
                       + "<ns1:tag1>"
                           + "<ns1:tag2>value</ns1:tag2>"
                       + "</ns1:tag1>"
                   + "</ns1:schema>";

        XPath xpath = XPathFactory.newInstance().newXPath();
        xpath.setNamespaceContext(new NamespaceContext() {

            public String getNamespaceURI(String arg0) {
                if("a".equals(arg0)) {
                    return "http://example.com";
                }
                return null;
            }

            public String getPrefix(String arg0) {
                return null;
            }

            public Iterator getPrefixes(String arg0) {
                return null;
            }

        });

        InputSource inputSource = new InputSource(new StringReader(xml));
        String result = (String) xpath.evaluate("/a:schema/a:tag1/a:tag2", inputSource, XPathConstants.STRING);
        System.out.println(result);
    }

}

输出

value

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