Java XPath NamespaceContext – 命名空间解析示例 · HowToDoInJava 中文系列教程

# Java XPath `NamespaceContext` – 命名空间解析示例 > 原文： [https://howtodoinjava.com/xml/xpath-namespace-resolution-example/](https://howtodoinjava.com/xml/xpath-namespace-resolution-example/) 在此 Java 示例中，我们将使用[`NamespaceContext`](https://docs.oracle.com/javase/7/docs/api/javax/xml/namespace/NamespaceContext.html)将 XPath 命名空间解析学习为 XML 文件，该文件具有命名空间声明和各自的用法。 ## 添加了 XML 文件的命名空间我已经创建了`sample.xml`文件并将其放在类路径中。 ```java <ns2:bookStore xmlns:ns2="http://bookstore.com/schemes"> <ns2:book id="1"> <ns2:name>Data Structure</ns2:name> </ns2:book> <ns2:book id="2"> <ns2:name>Java Core</ns2:name> </ns2:book> </ns2:bookStore> ``` ## 实现`NamespaceContext`以创建命名空间解析器该命名空间解析器可以与使用了命名空间定义的任何 XML 文件一起使用。它搜索 XML 文档本身内任何给定命名空间前缀（作为参数传递）的命名空间声明。因此**无需单独创建命名空间映射**。 ```java public class NamespaceResolver implements NamespaceContext { //Store the source document to search the namespaces private Document sourceDocument; public NamespaceResolver(Document document) { sourceDocument = document; } //The lookup for the namespace uris is delegated to the stored document. public String getNamespaceURI(String prefix) { if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) { return sourceDocument.lookupNamespaceURI(null); } else { return sourceDocument.lookupNamespaceURI(prefix); } } public String getPrefix(String namespaceURI) { return sourceDocument.lookupPrefix(namespaceURI); } @SuppressWarnings("rawtypes") public Iterator getPrefixes(String namespaceURI) { return null; } } ``` ## 使用`NamespaceResolver`并应用 XPath 现在，我们准备在 XML 文件上应用 xpath 表达式。 ```java //Want to read all book names from XML ArrayList<String> bookNames = new ArrayList<String>(); //Parse XML file DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setNamespaceAware(true); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse(new FileInputStream(new File("sample.xml"))); //Get XPath expression XPathFactory xpathfactory = XPathFactory.newInstance(); XPath xpath = xpathfactory.newXPath(); xpath.setNamespaceContext(new NamespaceResolver(doc)); XPathExpression expr = xpath.compile("//ns2:bookStore/ns2:book/ns2:name/text()"); //Search XPath expression Object result = expr.evaluate(doc, XPathConstants.NODESET); //Iterate over results and fetch book names NodeList nodes = (NodeList) result; for (int i = 0; i < nodes.getLength(); i++) { bookNames.add(nodes.item(i).getNodeValue()); } //Verify book names System.out.println(bookNames); ``` 上面程序的输出是： ```java [Data Structure, Java Core] ``` ## XPath 命名空间解析的完整源代码这是上面示例的完整源代码。 ```java import java.io.File; import java.io.FileInputStream; import java.util.ArrayList; import java.util.Iterator; import javax.xml.XMLConstants; import javax.xml.namespace.NamespaceContext; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.xpath.XPath; import javax.xml.xpath.XPathConstants; import javax.xml.xpath.XPathExpression; import javax.xml.xpath.XPathFactory; import org.w3c.dom.Document; import org.w3c.dom.NodeList; public class Main { public static void main(String[] args) throws Exception { //Want to read all book names from XML ArrayList<String> bookNames = new ArrayList<String>(); //Parse XML file DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setNamespaceAware(true); DocumentBuilder builder = factory.newDocumentBuilder(); Document doc = builder.parse(new FileInputStream(new File("sample.xml"))); //Get XPath expression XPathFactory xpathfactory = XPathFactory.newInstance(); XPath xpath = xpathfactory.newXPath(); xpath.setNamespaceContext(new NamespaceResolver(doc)); XPathExpression expr = xpath.compile("//ns2:bookStore/ns2:book/ns2:name/text()"); //Search XPath expression Object result = expr.evaluate(doc, XPathConstants.NODESET); //Iterate over results and fetch book names NodeList nodes = (NodeList) result; for (int i = 0; i < nodes.getLength(); i++) { bookNames.add(nodes.item(i).getNodeValue()); } //Verify book names System.out.println(bookNames); } } class NamespaceResolver implements NamespaceContext { //Store the source document to search the namespaces private Document sourceDocument; public NamespaceResolver(Document document) { sourceDocument = document; } //The lookup for the namespace uris is delegated to the stored document. public String getNamespaceURI(String prefix) { if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) { return sourceDocument.lookupNamespaceURI(null); } else { return sourceDocument.lookupNamespaceURI(prefix); } } public String getPrefix(String namespaceURI) { return sourceDocument.lookupPrefix(namespaceURI); } @SuppressWarnings("rawtypes") public Iterator getPrefixes(String namespaceURI) { return null; } } ``` 在评论部分让我知道您的问题。学习愉快！参考： [http://www.ibm.com/developerworks/library/x-nmspccontext/](https://www.ibm.com/developerworks/library/x-nmspccontext/)