java中评估字符串上的xpath并返回结果字符串的简单方法是啥

Posted 2023-02-26

【中文标题】java中评估字符串上的xpath并返回结果字符串的简单方法是啥

【英文标题】：What's a simple way in java to evaluate an xpath on a string and return a result stringjava中评估字符串上的xpath并返回结果字符串的简单方法是什么

【发布时间】：2011-05-10 23:54:54

【问题描述】：

一个简单的问题需要一个简单的答案。

例如：

String xml = "<car><manufacturer>toyota</manufacturer></car>";
String xpath = "/car/manufacturer";
assertEquals("toyota",evaluate(xml, xpath));

如何以简单易读的方式编写适用于任何给定格式良好的 xml 和 xpath 的评估方法。

显然有很多方法可以实现这一点，但大多数看起来都非常冗长。

我缺少任何可以实现此目的的简单方法/库？

对于返回多个节点的情况，我只想要这个的字符串表示。

【参考方案1】：

给你，用 Java SE 可以做到以下几点：

import java.io.StringReader;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;
import org.xml.sax.InputSource;

public class Demo 

    public static void main(String[] args) throws Exception 
        String xml = "<car><manufacturer>toyota</manufacturer></car>";
        String xpath = "/car/manufacturer";
        XPath xPath = XPathFactory.newInstance().newXPath();
        assertEquals("toyota",xPath.evaluate(xpath, new InputSource(new StringReader(xml))));
    

【参考方案2】：

对于这个用例，XMLUnit 库可能是一个完美的选择： http://xmlunit.sourceforge.net/userguide/html/index.html#Xpath%20Tests

它提供了一些额外的断言方法。

例如：

assertXpathEvaluatesTo("toyota", "/car/manufacturer",
    "<car><manufacturer>toyota</manufacturer></car>");

【参考方案3】：

使用来自https://github.com/guppy4j/libraries/tree/master/messaging-impl 的 Xml 类：

Xml xml = new Xml("<car><manufacturer>toyota</manufacturer></car>");
assertEquals("toyota", xml.get("/car/manufacturer"));

【参考方案4】：

到目前为止，我已经用三种语言写过assertXPath()。 Ruby 和 Python 是最好的，因为它们还可以通过 libxml2 解析具有其特性的 HTML，然后在它们上运行 XPath。对于 XML，或者对于没有像 < 这样的 javascript“小于”的小故障的精心控制的 HTML，这是我的断言套件：

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

private static @NonNull Document assertHtml(@NonNull String xml) 
    try 
        try 
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            factory.setNamespaceAware(false);
            DocumentBuilder builder = factory.newDocumentBuilder();
            ByteArrayInputStream stream = new ByteArrayInputStream(xml.replaceAll("i < len;", "i &lt; len;").getBytes());  //  Because JavaScript ruined HTML's ability to someday be real XML...
            return builder.parse(stream);
         catch (SAXParseException e) 
            if (e.getLocalizedMessage().startsWith("Unexpected token") && !xml.startsWith("<xml>"))
                return assertHtml("<xml>" + xml + "</xml>");

            throw e;  //  a GOTO to 2 lines down...
        
     catch (Throwable e) 
        fail(e.getLocalizedMessage());
    
    return null;


private static @NonNull List<String> assertXPaths(@NonNull Node node, @NonNull String xpathExpression)

    NodeList nodes = evaluateXPath(node, xpathExpression);
    List<String> values = new ArrayList<>();

    if (nodes != null)
        for (int i = 0; i < nodes.getLength(); i++) 
            Node item = nodes.item(i);
              //  item.getTextContent();
              //  item.getNodeName();
            values.add(item.getNodeValue());
        

    if (values.size() == 0)
        fail("XPath not found: " + xpathExpression + "\n\nin: " + nodeToString(node) + "\n");

    return values;


private static @NonNull Node assertXPath(@NonNull Node node, @NonNull String xpathExpression)

    NodeList nodes = evaluateXPath(node, xpathExpression);

    if (nodes != null && nodes.getLength() > 0)
        return nodes.item(0);

    fail("XPath not found: " + xpathExpression + "\n\nin: " + nodeToString(node) + "\n");
    return null;  //  this can't happen


private static NodeList evaluateXPath(@NonNull Node node, @NonNull String xpathExpression) 
    NodeList nodes = null;

    try 
        XPathExpression expr = xpath.compile(xpathExpression);
        nodes = (NodeList) expr.evaluate(node, XPathConstants.NODESET);
     catch (XPathExpressionException e) 
        fail(e.getLocalizedMessage());
    
    return nodes;


private static void assertXPath(Node node, String xpathExpression, String reference) 
    List<String> nodes = assertXPaths(node, xpathExpression);
    assertEquals(1, nodes.size());  // CONSIDER  decorate these assertion diagnostics with nodeToString(). And don't check for one text() - join them all together
    assertEquals(reference, nodes.get(0).trim());  // CONSIDER  same complaint:  We need to see the nodeToString() here


private static void refuteXPath(@NonNull Node node, @NonNull String xpathExpression) 
    NodeList nodes = evaluateXPath(node, xpathExpression);

    if (nodes.getLength() != 0)
        fail("XPath should not be found: " + xpathExpression);  // CONSIDER  decorate this with the contents of the node


private static @NonNull String nodeToString(@NonNull Node node) 
    StringWriter sw = new StringWriter();
    Transformer t = null;

    try 
        t = TransformerFactory.newInstance().newTransformer();
     catch (TransformerConfigurationException e) 
        fail(e.getLocalizedMessage());
    

    t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
    t.setOutputProperty(OutputKeys.INDENT, "yes");

    try 
        t.transform(new DOMSource(node), new StreamResult(sw));
     catch (TransformerException e) 
        fail(e.getLocalizedMessage());
    

    return sw.toString();

递归地使用它们，像这样：

    Document doc = assertHtml(myHtml);
    Node blockquote = assertXPath(doc, "//blockquote[ 'summary_7' = @id ]");

    assertXPath(blockquote, ".//span[ contains(., 'Mammal') and strong/text() = 'anteater' ]");

找到一个节点，然后断言相对于该节点的路径（通过.//）的好处是在失败时nodeToString() 只会报告节点内容，例如我的<blockquote>。断言诊断消息不会包含整个文档，因此非常易于阅读。