9

在下面的示例代码中，当源 xml 具有命名空间前缀时，任何采用“// elementName ”形式的 XPath 都会返回 null（请参见testWithNS()底部的代码）。

当源 xml 没有名称空间前缀时，所有列出的 XPath 表达式都返回一个节点（请参阅 参考资料testNoNS()）。

我知道我可以通过设置 NamespaceContext（如 中testWithNSContext()）、将 xml 解析为命名空间感知文档以及在 XPaths 中使用命名空间前缀来解决这个问题。但是我不想这样做，因为我的实际代码需要处理带有和不带有名称空间前缀的 xml。

我的问题是为什么它只是：

  • //测试
  • //孩子1
  • //孙子1
  • //child2

返回null，但所有其他示例都testWithNS()返回节点？

输出

testNoNS()
test = found
/test = found
//test = found
//test/* = found
//test/child1 = found
//test/child1/grandchild1 = found
//test/child2 = found
//child1 = found
//grandchild1 = found
//child1/grandchild1 = found
//child2 = found

testWithNS()
test = found
/test = found
//test = *** NOT FOUND ***
//test/* = found
//test/child1 = found
//test/child1/grandchild1 = found
//test/child2 = found
//child1 = *** NOT FOUND ***
//grandchild1 = *** NOT FOUND ***
//child1/grandchild1 = found
//child2 = *** NOT FOUND ***

testWithNSContext()
ns1:test = found
/ns1:test = found
//ns1:test = found
//ns1:test/* = found
//ns1:test/ns1:child1 = found
//ns1:test/ns1:child1/ns1:grandchild1 = found
//ns1:test/ns1:child2 = found
//ns1:child1 = found
//ns1:grandchild1 = found
//ns1:child1/ns1:grandchild1 = found
//ns1:child2 = found

代码

import java.io.StringReader;
import java.util.Iterator;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

import org.junit.Test;
import org.w3c.dom.Document;
import org.xml.sax.InputSource;

public class XPathBugTest {

    private String xmlDec = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>";
    private String xml = xmlDec + 
        "<test>" +
        "  <child1>" +
        "    <grandchild1/>" +
        "  </child1>" +
        "  <child2/>" +
        "</test>";
    private String xmlNs = xmlDec + 
        "<ns1:test xmlns:ns1=\"http://www.wfmc.org/2002/XPDL1.0\">" +
        "  <ns1:child1>" +
        "    <ns1:grandchild1/>" +
        "  </ns1:child1>" +
        "  <ns1:child2/>" +
        "</ns1:test>";

    final XPathFactory xpathFactory = XPathFactory.newInstance();
    final XPath xpath = xpathFactory.newXPath();

    @Test
    public void testNoNS() throws Exception {
        System.out.println("\ntestNoNS()");
        final Document doc = getDocument(xml);

        isFound("test", xpath.evaluate("test", doc, XPathConstants.NODE));
        isFound("/test", xpath.evaluate("/test", doc, XPathConstants.NODE));
        isFound("//test", xpath.evaluate("//test", doc, XPathConstants.NODE));
        isFound("//test/*", xpath.evaluate("//test/*", doc, XPathConstants.NODE));
        isFound("//test/child1", xpath.evaluate("//test/child1", doc, XPathConstants.NODE));
        isFound("//test/child1/grandchild1", xpath.evaluate("//test/child1/grandchild1", doc, XPathConstants.NODE));
        isFound("//test/child2", xpath.evaluate("//test/child2", doc, XPathConstants.NODE));
        isFound("//child1", xpath.evaluate("//child1", doc, XPathConstants.NODE));
        isFound("//grandchild1", xpath.evaluate("//grandchild1", doc, XPathConstants.NODE));
        isFound("//child1/grandchild1", xpath.evaluate("//child1/grandchild1", doc, XPathConstants.NODE));
        isFound("//child2", xpath.evaluate("//child2", doc, XPathConstants.NODE));
    }

    @Test
    public void testWithNS() throws Exception {
        System.out.println("\ntestWithNS()");
        final Document doc = getDocument(xmlNs);

        isFound("test", xpath.evaluate("test", doc, XPathConstants.NODE));
        isFound("/test", xpath.evaluate("/test", doc, XPathConstants.NODE));
        isFound("//test", xpath.evaluate("//test", doc, XPathConstants.NODE));
        isFound("//test/*", xpath.evaluate("//test/*", doc, XPathConstants.NODE));
        isFound("//test/child1", xpath.evaluate("//test/child1", doc, XPathConstants.NODE));
        isFound("//test/child1/grandchild1", xpath.evaluate("//test/child1/grandchild1", doc, XPathConstants.NODE));
        isFound("//test/child2", xpath.evaluate("//test/child2", doc, XPathConstants.NODE));
        isFound("//child1", xpath.evaluate("//child1", doc, XPathConstants.NODE));
        isFound("//grandchild1", xpath.evaluate("//grandchild1", doc, XPathConstants.NODE));
        isFound("//child1/grandchild1", xpath.evaluate("//child1/grandchild1", doc, XPathConstants.NODE));
        isFound("//child2", xpath.evaluate("//child2", doc, XPathConstants.NODE));
    }

    @Test
    public void testWithNSContext() throws Exception {
        System.out.println("\ntestWithNSContext()");
        final Document doc = getDocumentNS(xmlNs);

        xpath.setNamespaceContext(new MyNamespaceContext());

        isFound("ns1:test", xpath.evaluate("ns1:test", doc, XPathConstants.NODE));
        isFound("/ns1:test", xpath.evaluate("/ns1:test", doc, XPathConstants.NODE));
        isFound("//ns1:test", xpath.evaluate("//ns1:test", doc, XPathConstants.NODE));
        isFound("//ns1:test/*", xpath.evaluate("//ns1:test/*", doc, XPathConstants.NODE));
        isFound("//ns1:test/ns1:child1", xpath.evaluate("//ns1:test/ns1:child1", doc, XPathConstants.NODE));
        isFound("//ns1:test/ns1:child1/ns1:grandchild1", xpath.evaluate("//ns1:test/ns1:child1/ns1:grandchild1", doc, XPathConstants.NODE));
        isFound("//ns1:test/ns1:child2", xpath.evaluate("//ns1:test/ns1:child2", doc, XPathConstants.NODE));
        isFound("//ns1:child1", xpath.evaluate("//ns1:child1", doc, XPathConstants.NODE));
        isFound("//ns1:grandchild1", xpath.evaluate("//ns1:grandchild1", doc, XPathConstants.NODE));
        isFound("//ns1:child1/ns1:grandchild1", xpath.evaluate("//ns1:child1/ns1:grandchild1", doc, XPathConstants.NODE));
        isFound("//ns1:child2", xpath.evaluate("//ns1:child2", doc, XPathConstants.NODE));
    }

    private void isFound(String xpath, Object object) {
        System.out.println(xpath + " = " + (object == null ? "*** NOT FOUND ***" : "found"));
    }

    private Document getDocument(final String xml) throws Exception {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        return factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));        
    }

    private Document getDocumentNS(final String xml) throws Exception {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        return factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
    }

    public class MyNamespaceContext implements NamespaceContext {
        @Override
        public String getNamespaceURI(String prefix) {
            if ("ns1".equals(prefix)) {
                return "http://www.wfmc.org/2002/XPDL1.0";
            }
            return XMLConstants.NULL_NS_URI;
        }
        @Override
        public String getPrefix(String uri) {
            throw new UnsupportedOperationException();
        }
        @Override
        public Iterator getPrefixes(String uri) {
            throw new UnsupportedOperationException();
        }
    }
}

撒克逊测试后更新

我现在已经使用 Saxon 测试了相同的代码，将 XPahtFactory 行更改为此

final XPathFactory xpathFactory = new net.sf.saxon.xpath.XPathFactoryImpl();

testWithNS()作为回报，使用 Saxon 所有行，*** NOT FOUND ***而不是像默认 Xalan 实现那样仅使用像 '// elementName ' 这样的行。

鉴于我正在使用非命名空间感知文档构建器工厂来解析 xml，为什么这些 xpath 都不起作用，而只有一些与 Xalan 一起工作？

4

2 回答 2

3

如果要忽略命名空间，可以使用local-nameXPath 函数：

//*[local-name()='grandchild1']
于 2013-07-24T13:30:24.637 回答
2

鉴于我正在使用非命名空间感知文档构建器工厂来解析 xml，为什么这些 xpath 都不起作用，而只有一些与 Xalan 一起工作？

XPath 语言仅在名称空间格式良好的 XML 文档和片段上定义。如果您在没有命名空间支持的情况下进行解析，那么所有的赌注都没有了，无法保证任何 XPath 表达式都能在由非命名空间感知解析器创建的 DOM 上正常工作（即使相关文档不使用任何命名空间） .

我知道在给它提供非 NS 感知的文档时，我已经看到 Java 内置 XSLT 处理器的行为非常不一致。

于 2013-09-29T22:59:02.990 回答