java - 如何通过 XPATH 更新 Java 中需要不同值的多个节点？

Question

当需要处理不同名称的字段时，如何通过一个 XPATH 语句更新多个节点？

Answer 1

I'm not sure what your goals were in posting this question, however I see several issues with your own answer.

• XPath is a tool for applying predicates to DOM trees. It makes no sense to use XPath to select a larger set of nodes than you need, and then apply your own predicates to the list of nodes that it returns.
• Your XPath expression contains multiple orthogonal terms. This is less efficient to evaluate, and will quickly become unmanageable as you add additional terms.
• The expressions that you're using -- retrieving the text nodes and then navigating to the parent Element -- doesn't make a lot of sense. I suppose that you're looking to only select nodes that already have text, but if you're doing a global search and replace I'm not sure that's a reasonable assumption. If I were to inherit your code I'd certainly want to see tests that demonstrate both behaviors, as an indication that you intended that behavior.
• Long chains of if/else statements are notoriously difficult to comprehend. They're also difficult to test, as you have to craft a test suite that executes all possible paths through the code.
• The body of your if statements is repeated code, violating the DRY principal. Given your need to navigate upward from the selected nodes, this opens up a possibility for errors -- or copy-and-paste code that has to be changed in multiple places if you ever change the way you specify your expressions.

In my opinion, it's far better to extract a method that selects nodes and performs changes for a single expression at a time. Starting from your code, and letting my IDE fix some of the syntax errors, I ended up with this (however, I haven't written testcases):

public static void main(String[] args) throws Exception  
{  
     DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
     DocumentBuilder builder = factory.newDocumentBuilder();  
     Document doc = builder.parse(new File("path/to/file.xml"));  

     changeNodeText(doc, "/PersonList/Person/Age", "42");
     changeNodeText(doc, "/PersonList/Person/Name", "Batman");
}  


public static void changeNodeText(Node context, String xpath, String value)
throws XPathExpressionException
{
    XPathFactory xFactory = XPathFactory.newInstance();
    XPath xPath = xFactory.newXPath();
    XPathExpression expression = xPath.compile(xpath);
    NodeList nodes = (NodeList)expression.evaluate(context, XPathConstants.NODESET);
    for (int i = 0; i < nodes.getLength(); i++)
    {
        Node node = nodes.item(i);
        node.setTextContent(value);
    }
}

Some of the key features (aside from the XPath-specific comments I made above):

• The function name makes it clear that you're changing the text of a node.
• You can easily see the paths that you're updating; you don't have to walk through code to figure out what it's doing.
• You can test this with two testcases (positive and negative) and infer that it will work anywhere.
• It uses the setTextContent() method, which IMO has a better specification than setNodeValue() (which will fail unless you pass text nodes).
• If you ever have to add a namespace mapping, you can do it in one place. Ditto if you decide that you only want to change elements that already have text nodes.

Answer 2

给定这样的模式：

<?xml version="1.0" encoding="UTF-8"?>  
<PersonList>  
    <Person>  
          <Name>Adam West </Name>  
          <Age> 72 </Age>
    </Person>  
</PersonList>  

以下代码将更新名称字段Batman和年龄字段42

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.Node;
import org.w3c.dom.NodeList;
    public static void main(String[] args) throws Exception  
    {  
         DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();  
         DocumentBuilder builder = factory.newDocumentBuilder();  
         Document doc = builder.parse(new File("path/to/file.xml"));  

         XPathFactory xFactory = XPathFactory.newInstance();  
         XPath xPath = xFactory.newXPath();  
         XPathExpression expression = xPath.compile("PersonList/Person/Age/text() | PersonList/Person/Name/text()");  

         NodeList nodes = (NodeList) expression.evaluate(doc,XPathConstants.NODESET);  
        for(int i = 0; i <nodes.getLength() i++)  
        {  
               Node node = nodes.item(i);   
               if(node.getPArentNode().getNodeName().equals("Name")  
               {  
                    node.setNodeValue("Batman");  
               }   else  
               {  
                   node.setNodeValue("42"); // you may need more else/if blocks / switch
               }  
         }  
    }