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  3. xml - Why is my .evaluate function returning no value? Java DOM parsing using Xpath - Stack Overflow

xml - Why is my .evaluate function returning no value? Java DOM parsing using Xpath - Stack Overflow

admin2025-04-19  1

Currently I am tryin to retreive the lists of all Archive and individual tags within the connections set in the events section, so I can sum the result of both lists together and use them comparitively as well as counting the instaces of an element having only 1 associated artifact in the individuals section. Currently however the node evaluation of the file path returns nothing, not even a null value, I am aware of the inconsistant spelling, however I don't it is currently causing the problem and I will rectify it once the actual problem is sorted. Can anyone shed light as to what may be causing the issue?

package src;
import java.io.File;
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 javax.xml.parsers.DocumentBuilder;
import .w3c.dom.Document;
import .w3c.dom.NodeList;
import .w3c.dom.Element; //installing necessary libraries

public class SearchXML
{
   public static void main(String[] args)
   {    
      try //try catch required to stop document builder and parse throwing exceptions without excessive throws statements
      {           
         File InputFile = new File("Example.xml"); //File to search
          
         DocumentBuilderFactory DBFactory = DocumentBuilderFactory.newInstance(); //Initialise the DOM document builder to create DOM documents
         DocumentBuilder DocBuilder = DBFactory.newDocumentBuilder(); //Obtain instance of a DOM document
         Document XML_Document = DocBuilder.parse(InputFile); //Parsing the file
         
         XPathFactory XPathfactory = XPathFactory.newInstance();
         
         
         String MostConnections = "";
         int ArtifactCount = 0;
         int IndividualCount = 0;
         int HighNumConnection = 0;
         int SingleArtifactIndividuals = 0;//Initialising variables
         
         
       //counting  highest number of event connections
         NodeList EventNodes = XML_Document.getElementsByTagName("Events");
         for(int i = 1 ; i < EventNodes.getLength() ; i++)
         {
            XPath EventArtifact = XPathfactory.newXPath();
            XPath EventIndividual = XPathfactory.newXPath();//creating temporary path variables
            
            NodeList nodes;
            
            Element EventElement = (Element) EventNodes.item(i);
            String EventArtifactPath = ("//ArchiveSystem/Events/Event[@id=E00"+i+"]/Connections/Artefacts/Artefact");//creates a path to the artifact connection nodes for each Event element
            String EventIndividualPath = ("//ArchiveSystem/Events/Event[@id=E00"+i+"]/Connections/Individuals/Individual");//same as above for individuals
            
            
            javax.xml.xpath.XPathExpression NumEventArtifacts = EventArtifactpile(EventArtifactPath);
            Object result  = NumEventArtifacts.evaluate(XML_Document, XPathConstants.NODESET);
            nodes = (NodeList) result;
            System.out.println(nodes.getLength());
            
            
            //GetLength function for attribute and individual connections
            
            //ArtifactCount =
            //IndividualCount = 
            //System.out.println(ArtifactCount);
            //System.out.println(IndividualCount);
            
            if (ArtifactCount+IndividualCount > HighNumConnection) //comparison of number of connections
            {
                MostConnections = EventElement.getAttribute("id");//updating the event with the most connections
                HighNumConnection = ArtifactCount+IndividualCount;//updating new highest number of connections
            }
            
         }
         System.out.println("The Event with the most connections is " + MostConnections + "with "+HighNumConnection+".");
         
         System.out.println("");
         
         NodeList IndividualNodes = XML_Document.getElementsByTagName("Indiviuals");
         
         for(int j = 0 ; j < IndividualNodes.getLength() ; j++)
         {
            XPath IndividualArtefact = XPathfactory.newXPath();//creating a temporary variable for the node path
            
            Element IndidividualElement = (Element) IndividualNodes.item(j);
            
            XPathExpression IndividualArtefactPath = IndividualArtefactpile("/ArchiveSystem/Individuals/Individual[@id=I00"+j+"]/Connections/Artifacts");
            //GetLength function for attribute  connections
            ArtifactCount = ((NodeList)IndividualArtefactPath.evaluate(XML_Document, XPathConstants.NODESET)).getLength();;//fetching length of node lists from the path;
            
            if (ArtifactCount == 1)
            {
                SingleArtifactIndividuals++; //updating number of individuals with only 1 artifact
            }
            
         }
         
         System.out.println("The number of individuals with only one artifact connection is " +SingleArtifactIndividuals+".");
         
      }
         catch (Exception exception)
      {
         exception.printStackTrace();//print caught error location
      }
   }

}

Heres the XML:

<?xml version="1.0" encoding="UTF-8" ?>
<ArchiveSystem>

<Artefacts>

    <Artefact id="A001">
        <Name>ArtifactTest1</Name>
        <Description>ArtifactTest1</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A002">
        <Name>ArtifactTest2</Name>
        <Description>ArtifactTest2</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A003">
        <Name>ArtifactTest3></Name>
        <Description>ArtifactTest3</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A004">
        <Name>ArtifactTest4</Name>
        <Description>ArtifactTest4</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A005">
        <Name>ArtifactTest5</Name>
        <Description>ArtifactTest5</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>
</Artefacts>

<Events>

    <Event id="E001">
        <Name>EventTest1</Name>
        <Date>2001</Date>
        <Location>TestLocation1</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E002">
        <Name>EventTest2</Name>
        <Date>2002</Date>
        <Location>TestLocation2</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E003">
        <Name>EventTest3</Name>
        <Date>2003</Date>
        <Location>TestLocation3</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E004">
        <Name>EventTest4</Name>
        <Date>2004</Date>
        <Location>TestLocation4</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>

            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
                <Individual>I004</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E005">
        <Name>EventTest5</Name>
        <Date>2005</Date>
        <Location>TestLocation5</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
                <Artifact>A005</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
                <Individual>I004</Individual>
                <Individual>I005</Individual>
            </Individuals>
        </Connections>
    </Event>
</Events>

<Individuals>

    <Individual id="I001">
        <Name>John Smith</Name>
        <Lifespan>2000-2101</Lifespan>
        <Role>RoleTest1</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I002">
        <Name>Jane Smith</Name>
        <Lifespan>2000-2102</Lifespan>
        <Role>RoleTest2</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I003">
        <Name>John Doe</Name>
        <Lifespan>2000-2103</Lifespan>
        <Role>RoleTest3</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I004">
        <Name>Jane Doe</Name>
        <Lifespan>2000-2104</Lifespan>
        <Role>RoleTest4</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
                <Event>E004</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I005">
        <Name>Person X</Name>
        <Lifespan>2000-2105</Lifespan>
        <Role>RoleTest5</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
                <Artifact>A005</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
                <Event>E004</Event>
                <Event>E005</Event>
            </Events>
        </Connections>
    </Individual>
</Individuals>

</ArchiveSystem>

Currently I am tryin to retreive the lists of all Archive and individual tags within the connections set in the events section, so I can sum the result of both lists together and use them comparitively as well as counting the instaces of an element having only 1 associated artifact in the individuals section. Currently however the node evaluation of the file path returns nothing, not even a null value, I am aware of the inconsistant spelling, however I don't it is currently causing the problem and I will rectify it once the actual problem is sorted. Can anyone shed light as to what may be causing the issue?

package src;
import java.io.File;
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 javax.xml.parsers.DocumentBuilder;
import .w3c.dom.Document;
import .w3c.dom.NodeList;
import .w3c.dom.Element; //installing necessary libraries

public class SearchXML
{
   public static void main(String[] args)
   {    
      try //try catch required to stop document builder and parse throwing exceptions without excessive throws statements
      {           
         File InputFile = new File("Example.xml"); //File to search
          
         DocumentBuilderFactory DBFactory = DocumentBuilderFactory.newInstance(); //Initialise the DOM document builder to create DOM documents
         DocumentBuilder DocBuilder = DBFactory.newDocumentBuilder(); //Obtain instance of a DOM document
         Document XML_Document = DocBuilder.parse(InputFile); //Parsing the file
         
         XPathFactory XPathfactory = XPathFactory.newInstance();
         
         
         String MostConnections = "";
         int ArtifactCount = 0;
         int IndividualCount = 0;
         int HighNumConnection = 0;
         int SingleArtifactIndividuals = 0;//Initialising variables
         
         
       //counting  highest number of event connections
         NodeList EventNodes = XML_Document.getElementsByTagName("Events");
         for(int i = 1 ; i < EventNodes.getLength() ; i++)
         {
            XPath EventArtifact = XPathfactory.newXPath();
            XPath EventIndividual = XPathfactory.newXPath();//creating temporary path variables
            
            NodeList nodes;
            
            Element EventElement = (Element) EventNodes.item(i);
            String EventArtifactPath = ("//ArchiveSystem/Events/Event[@id=E00"+i+"]/Connections/Artefacts/Artefact");//creates a path to the artifact connection nodes for each Event element
            String EventIndividualPath = ("//ArchiveSystem/Events/Event[@id=E00"+i+"]/Connections/Individuals/Individual");//same as above for individuals
            
            
            javax.xml.xpath.XPathExpression NumEventArtifacts = EventArtifactpile(EventArtifactPath);
            Object result  = NumEventArtifacts.evaluate(XML_Document, XPathConstants.NODESET);
            nodes = (NodeList) result;
            System.out.println(nodes.getLength());
            
            
            //GetLength function for attribute and individual connections
            
            //ArtifactCount =
            //IndividualCount = 
            //System.out.println(ArtifactCount);
            //System.out.println(IndividualCount);
            
            if (ArtifactCount+IndividualCount > HighNumConnection) //comparison of number of connections
            {
                MostConnections = EventElement.getAttribute("id");//updating the event with the most connections
                HighNumConnection = ArtifactCount+IndividualCount;//updating new highest number of connections
            }
            
         }
         System.out.println("The Event with the most connections is " + MostConnections + "with "+HighNumConnection+".");
         
         System.out.println("");
         
         NodeList IndividualNodes = XML_Document.getElementsByTagName("Indiviuals");
         
         for(int j = 0 ; j < IndividualNodes.getLength() ; j++)
         {
            XPath IndividualArtefact = XPathfactory.newXPath();//creating a temporary variable for the node path
            
            Element IndidividualElement = (Element) IndividualNodes.item(j);
            
            XPathExpression IndividualArtefactPath = IndividualArtefactpile("/ArchiveSystem/Individuals/Individual[@id=I00"+j+"]/Connections/Artifacts");
            //GetLength function for attribute  connections
            ArtifactCount = ((NodeList)IndividualArtefactPath.evaluate(XML_Document, XPathConstants.NODESET)).getLength();;//fetching length of node lists from the path;
            
            if (ArtifactCount == 1)
            {
                SingleArtifactIndividuals++; //updating number of individuals with only 1 artifact
            }
            
         }
         
         System.out.println("The number of individuals with only one artifact connection is " +SingleArtifactIndividuals+".");
         
      }
         catch (Exception exception)
      {
         exception.printStackTrace();//print caught error location
      }
   }

}

Heres the XML:

<?xml version="1.0" encoding="UTF-8" ?>
<ArchiveSystem>

<Artefacts>

    <Artefact id="A001">
        <Name>ArtifactTest1</Name>
        <Description>ArtifactTest1</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A002">
        <Name>ArtifactTest2</Name>
        <Description>ArtifactTest2</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A003">
        <Name>ArtifactTest3></Name>
        <Description>ArtifactTest3</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A004">
        <Name>ArtifactTest4</Name>
        <Description>ArtifactTest4</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>

    <Artefact id="A005">
        <Name>ArtifactTest5</Name>
        <Description>ArtifactTest5</Description>
        <Type>Test</Type>
        <DOC>2025</DOC>
    </Artefact>
</Artefacts>

<Events>

    <Event id="E001">
        <Name>EventTest1</Name>
        <Date>2001</Date>
        <Location>TestLocation1</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E002">
        <Name>EventTest2</Name>
        <Date>2002</Date>
        <Location>TestLocation2</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E003">
        <Name>EventTest3</Name>
        <Date>2003</Date>
        <Location>TestLocation3</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E004">
        <Name>EventTest4</Name>
        <Date>2004</Date>
        <Location>TestLocation4</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>

            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
                <Individual>I004</Individual>
            </Individuals>
        </Connections>
    </Event>

    <Event id="E005">
        <Name>EventTest5</Name>
        <Date>2005</Date>
        <Location>TestLocation5</Location>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
                <Artifact>A005</Artifact>
            </Artifacts>
            <Individuals>
                <Individual>I001</Individual>
                <Individual>I002</Individual>
                <Individual>I003</Individual>
                <Individual>I004</Individual>
                <Individual>I005</Individual>
            </Individuals>
        </Connections>
    </Event>
</Events>

<Individuals>

    <Individual id="I001">
        <Name>John Smith</Name>
        <Lifespan>2000-2101</Lifespan>
        <Role>RoleTest1</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I002">
        <Name>Jane Smith</Name>
        <Lifespan>2000-2102</Lifespan>
        <Role>RoleTest2</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I003">
        <Name>John Doe</Name>
        <Lifespan>2000-2103</Lifespan>
        <Role>RoleTest3</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I004">
        <Name>Jane Doe</Name>
        <Lifespan>2000-2104</Lifespan>
        <Role>RoleTest4</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
                <Event>E004</Event>
            </Events>
        </Connections>
    </Individual>

    <Individual id="I005">
        <Name>Person X</Name>
        <Lifespan>2000-2105</Lifespan>
        <Role>RoleTest5</Role>
        <Connections>
            <Artifacts>
                <Artifact>A001</Artifact>
                <Artifact>A002</Artifact>
                <Artifact>A003</Artifact>
                <Artifact>A004</Artifact>
                <Artifact>A005</Artifact>
            </Artifacts>
            <Events>
                <Event>E001</Event>
                <Event>E002</Event>
                <Event>E003</Event>
                <Event>E004</Event>
                <Event>E005</Event>
            </Events>
        </Connections>
    </Individual>
</Individuals>

</ArchiveSystem>
  • java
  • xml
  • xpath
Share Improve this question asked Mar 4 at 13:01 WeakTexas 68965WeakTexas 68965 33 bronze badges 5
  • 1 It exists alright, It's given me feedback from its location before, also coding isn't my job yet, so currently convention isn't the top of my list – WeakTexas 68965 Commented Mar 4 at 13:28
  • 1 You have misspelled Artifacts/Artifact: //ArchiveSystem/Events/Event[@id=E00"+i+"]/Connections/Artefacts/Artefact – LMC Commented Mar 4 at 14:40
  • 1 @LMC I've changed that and its not affected anything – WeakTexas 68965 Commented Mar 4 at 14:59
  • 1 @WeakTexas68965 Try surrounding the id value with single-quote like so: //ArchiveSystem/Events/Event[@id='E00"+i+"']/Connections/Artifacts/Artifact. – devxgb Commented Mar 4 at 15:15
  • @G_Basak that has fixed it, thank you very much – WeakTexas 68965 Commented Mar 4 at 15:52
Add a comment  | 

1 Answer 1

Reset to default 0

You need to put quotes around a string literal.

[@id=E001] looks for an element named E001. It should be [@id="E001"] (with single or double quotes, it doesn't matter).

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