# 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/)