Parsing Xml file in java to fetch the element matching given tag value-CodePudding

I have an xml as follow:

<root>

<outer>
<name>abc</name>
<age>20</age>
</outer>

<outer>
<name>def</name>
<age>30</age>
</outer>

<outer>
<name>ghi</name>
<age>40</age>
</outer>


</root>

I want to fetch the value of age tag for a given value of name tag?

One way is that I can prepare a map of name to age by parsing this xml using Document interface.

But is there any api that I can just call for Document interface in which I can say fetch element where name is say,ghi, and then i can iterate all atributes to get age attribute or any other simple way to get age where name value is,say ghi?

CodePudding user response：

XPath is a very expressive API that can be used to select the elements.

/root/outer[name = "ghi"]/age

This article https://www.baeldung.com/java-xpath provides a pretty good overview and explanation of how to apply an XPath in Java.

Adjusting one of their code samples for your XPath:

String name = "ghe";

DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = builderFactory.newDocumentBuilder();
Document xmlDocument = builder.parse(this.getFile());
XPath xPath = XPathFactory.newInstance().newXPath();

String expression = "/root/outer[name="   "'"   name   "'"   "]/age";
node = (Node) xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODE);

CodePudding user response：

Turns out java does come with an XPath evaluator in the javax.xml.xpath package, which makes this trivial:

import java.io.File;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;

public class Demo {
    public static void main(String[] args) throws Exception {
        String name = "ghi";
        // XPath expression to find an outer tag with a given name tag
        // and return its age tag
        String expression = String.format("/root/outer[name='%s']/age", name);
        
        // Parse an XML document
        DocumentBuilder builder
            = DocumentBuilderFactory.newInstance().newDocumentBuilder();
        Document document = builder.parse(new File("example.xml"));

        // Get an XPath object and evaluate the expression
        XPath xpath = XPathFactory.newInstance().newXPath();
        int age = xpath.evaluateExpression(expression, document, Integer.class);

        System.out.println(name   " is "   age   " years old");       
    }
}

Example use:

$ java Demo.java
ghi is 40 years old