Java Parsing iTunes XML library using XPath

Question

So I'm trying to create a method that allows me to input a track ID that will then return the track name which belongs to the track ID.

I am required to use XPath to parse the XML document into java which will in turn serialize a new library. A sample of my XML document is here:


    
        Major Version
        1
        Minor Version
        1
        Date
        2015-03-16T15:04:23Z
        Application Version
        12.1.0.71
        Features
        5
        Show Content Ratings
        
        Music Folder
        
        file://localhost/C:/Users/Mark/Music/iTunes/iTunes%20Media/
        
        Library Persistent ID
        3B01AE08EA513C21
        Tracks
        
            646
            
            Track ID
            646
            Name
            Save Me
            Artist
            Avenged Sevenfold
            Album Artist
            Avenged Sevenfold
            Album
            Nightmare
            Genre
            Metal
            Kind
            MPEG audio file
            Size
            23257166
            Total Time
            656535
            Disc Number
            1
            Disc Count
            1
            Track Number
            11
            Track Count
            11
            Year
            2010
            Date Modified
            2012-10-21T22:07:20Z
            Date Added
            2012-10-21T22:07:20Z
            Bit Rate
            276
            Sample Rate
            44100
            Play Count
            2
            Play Date
            3415934327
            Play Date UTC
            2012-03-30T06:38:47Z
            Artwork Count
            1
            Persistent ID
            0000000000001389
            Track Type
            File
            Location
            
            file://localhost/C:/Users/Mark/Music/Avenged%20Sevenfold/Nightmare/11%20-%20Save%20Me.mp3
            
            File Folder Count
            2
            Library Folder Count
            1
        
        648
        
            Track ID
            648
            Name
            Welcome 2 Hell
            Artist
            Bad Meets Evil
            Album Artist
            Bad Meets Evil
            Composer
            Havoc, Magnedo7
            Album
            Hell: The Sequel (Deluxe Edition)
            Genre
            Rap
            Kind
            MPEG audio file
            Size
            7467977
            Total Time
            177606
            Track Number
            1
            Year
            2011
            Date Modified
            2012-10-21T22:07:20Z
            Date Added
            2012-10-21T22:07:20Z
            Bit Rate
            320
            Sample Rate
            44100
            Play Count
            3
            Play Date
            3424485861
            Play Date UTC
            2012-07-07T06:04:21Z
            Skip Count
            2
            Skip Date
            2012-11-26T14:02:44Z
            Artwork Count
            1
            Persistent ID
            000000000000138A
            Track Type
            File
            Location
            
            file://localhost/C:/Users/Mark/Music/Bad%20Meets%20Evil/Hell_%20The%20Sequel%20(Deluxe%20Edition)/01%20-%20Welcome%202%20Hell.mp3
            
            File Folder Count
            2
            Library Folder Count
            1

Now, I'm fairly new to XPath and XML in general and am struggling to navigate the iTunes XML file, due to it's complexity and massive size.

So far my thoughts are to navigate to the 646 to check the id, then to the track name Save Me using "//dict/key[.="646"]/string[1]/text()".

This produces NULL. The code i have written in Java so far is:

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;


public class XMLparse {

    public XMLparse(){
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        DocumentBuilder builder;
        Document doc = null;
        try {
            builder = factory.newDocumentBuilder();
            doc = builder.parse(new File("C:\musicLibrary.xml"));

            // Create XPathFactory object
            XPathFactory xpathFactory = XPathFactory.newInstance();

            // Create XPath object
            XPath xpath = xpathFactory.newXPath();

            int id = 646;

            String name = getTrackNameById(doc, xpath, id);
            System.out.println("Track Name with ID " + id + ": " + name);

        } catch (ParserConfigurationException | SAXException | IOException e) {
            e.printStackTrace();
        }

    }

    public static String getTrackNameById(Document doc, XPath xpath, int id) {
        String name = null;
        try {
            XPathExpression expr = xpath.compile("//dict/integer[.="+id+"]/string[1]/text()");
            name = (String) expr.evaluate(doc, XPathConstants.STRING);
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }

        return name;
    }

}

Any help will be greatly appreciated.

EDIT:

Using Mathias Müller's suggestion produced the correct result, "Save Me" for track 646 as expected. However when I input another track ID it also returns "Save Me", which is incorrect.

I've no idea why it is doing this as I thought it would only return the track name of the ID i input, yet it returns a different track name?

SECOND EDIT:

-Included more of the XML

THIRD EDIT:

Changed the XPath expression to //dict[integer ="+id+"]/string[1]/text(), using Mathias' advice. This is working perfectly.

Mathias M&#252;ller · Accepted Answer

I cannot comment on the Java code, but I can explain to you the XPath expression you should use. Assuming the input sample you have shown, applying

//dict[key='646']/dict/key[. = 'Name']/following-sibling::*[1]

will return

Save Me

which is the element you were looking for. To only select its text content, use

//dict[key='646']/dict/key[. = 'Name']/following-sibling::*[1]/text()

and the result will be

Save Me

The path expression works as follows:

//dict                    select `dict` elements anywhere in the document
[key='646']               but only if they have an immediate child `key` whose text
                          content is equal to "646"
/dict                     select their child elements called `dict`
/key[. = 'Name']          of those `dict` elements select their child elements `key`,
                          but only if their text content is equal to "Name"
/following-sibling::*[1]  of those `key` elements, select the first following sibling
                          element
/text()                   and select its text content

Your original expression, relying on the position of the string element, also works with minor changes:

//dict[key ="646"]/dict/string[1]/text()

Java Parsing iTunes XML library using XPath

Answers (1)

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