How to Merge two XMLs in Java

Question

I am trying to merge two xmls in Java. I am using STaX API to write these XMLs. I searched a lot on internet on how to merge xmls but none seems as straight forward as C#. Is there any straight-forward way of doing this in Java using StAX? Probably xslt would not be the right solution since the file size can be big.

File1.xml

<TestCaseBlock>
    <TestCase TestCaseID="1">
        <Step ExecutionTime="2011-03-29 12:08:31 EST">
            <Status>Passed</Status>
            <Description>foo</Description>
            <Expected>foo should pass</Expected>
            <Actual>foo passed</Actual>
        </Step>
       </TestCase>
</TestCaseBlock> 

File2.xml

<TestCaseBlock>
    <TestCase TestCaseID="2">
        <Step ExecutionTime="2011-03-29 12:08:32 EST">
            <Status>Failed</Status>
            <Description>test something</Description>
            <Expected>something expected</Expected>
            <Actual>not as expected</Actual>
        </Step>
    </TestCase>
</TestCaseBlock>

Merged.xml

<TestCaseBlock>
<TestCase TestCaseID="1">
    <Step ExecutionTime="2011-03-29 12:08:33 EST">
        <Status>Passed</Status>
        <Description>foo</Description>
        <Expected>foo should pass</Expected>
        <Actual>foo passed</Actual>
    </Step>
</TestCase>
<TestCase TestCaseID="2">
    <Step ExecutionTime="2011-03-29 12:08:34 EST">
        <Status>Failed</Status>
        <Description>test something</Description>
        <Expected>something expected</Expected>
        <Actual>not as expected</Actual>
    </Step>
</TestCase>
</TestCaseBlock>

Izy

see also https://mcmap.net/q/779029/-merge-two-xml-files-in-java – Barytone

Answer 1

I have a solution that works for me. Now experts, please advise if this is the way to go.

Thanks, -Nilesh

    XMLEventWriter eventWriter;
    XMLEventFactory eventFactory;
    XMLOutputFactory outputFactory = XMLOutputFactory.newInstance();
    XMLInputFactory inputFactory = XMLInputFactory.newInstance();
    eventWriter = outputFactory.createXMLEventWriter(new FileOutputStream("testMerge1.xml"));
    eventFactory = XMLEventFactory.newInstance();
    XMLEvent newLine = eventFactory.createDTD("\n");                
    // Create and write Start Tag
    StartDocument startDocument = eventFactory.createStartDocument();
    eventWriter.add(startDocument);
    eventWriter.add(newLine);
    StartElement configStartElement = eventFactory.createStartElement("","","TestCaseBlock");
    eventWriter.add(configStartElement);
    eventWriter.add(newLine);
    String[] filenames = new String[]{"test1.xml", "test2.xml","test3.xml"};
    for(String filename:filenames){
           XMLEventReader test = inputFactory.createXMLEventReader(filename,
                             new FileInputStream(filename));
        while(test.hasNext()){
            XMLEvent event= test.nextEvent();
        //avoiding start(<?xml version="1.0"?>) and end of the documents;
        if (event.getEventType()!= XMLEvent.START_DOCUMENT && event.getEventType() != XMLEvent.END_DOCUMENT)
                eventWriter.add(event);         
        eventWriter.add(newLine);
            test.close();
        }           
    eventWriter.add(eventFactory.createEndElement("", "", "TestCaseBlock"));
    eventWriter.add(newLine);
    eventWriter.add(eventFactory.createEndDocument());
    eventWriter.close();

Izy

Where is inputFactory created in the code? Could you please modify the code to add the same? – Itemize

Answer 2

General solution still would be XSLT, but you'd need to combine two files into one big XML first with a wrapper element (XSLT works with one input source).

<root>
    <TestCaseBlock>
        <TestCase TestCaseID="1">
        ...
        </TestCase>
    </TestCaseBlock>
    <TestCaseBlock>
        <TestCase TestCaseID="2">
        ...
        </TestCase>
    </TestCaseBlock>
</root>

Then just do XSLT for match="//TestCase", and dump all test cases out, ignoring what test case block they belong to.

And don't worry about performance until you have tried. XML APIs in JAva are getting much better than in 2003.

This is stylesheet you need:

<?xml version="1.0" encoding="ISO-8859-1"?>

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

    <xsl:output method="xml" encoding="UTF-8" indent="yes"/>

    <xsl:template match="/">
            <TestCaseBlock>
                <xsl:apply-templates/>
            </TestCaseBlock>
    </xsl:template>

    <xsl:template match="//TestCase">
          <xsl:copy-of select="."/> 
    </xsl:template>

</xsl:stylesheet>

Tested, it works.

BTW, this XSLT was compiled and executed on this (small) example in 1ms.

Unplaced

Hi, thanks for the reply. I still would need TestCaseBlock though. It is common for all test cases, so I could probably remove it from individual xmls and keep it as a wrapper element. How would I combine two xml files into one file with wrapper element TestCaseBlock? Thanks again – Izy

I have a solution that works for me. I basically built on top of your idea. I used TestCaseBlock as a wrapper element and used XMLEventReader to dump test case tags. Stackoverflow isn't allowing me to answer my own question before 24 hrs :) I will post my code tomorrow for experts to review and suggest. – Izy

You don't need to read original TestCaseBlock. Create you own :) – Unplaced

As long as your solution works for you, experts will be happy! :D – Unplaced

Thanks for the xslt. I am going to save it :) – Izy

Answer 3

If structure is regular enough so you can use data binding, I would actually consider binding XML from both files into objects using JAXB, then merging objects, serializing back as XML. If file sizes are big you can also just bind sub-trees; for this you use XMLStreamReader (from Stax api, javax.xml.stream) to iterate to element that is the root, bind that element (and its children) to object you want, iterate to next root element.

Corina

Hi, I think that is an interesting approach. I will search on JAXB.Do you have a quick example? Could you please take a look at my solution and suggest if my approach isn't correct? Thanks. – Izy

Your solution looks correct to me in general. Just remember to close input reader. As to JAXB, online tutorials should work fine; you just create bean type with setters, getters, create context, marshaller/unmarshaller and so on. – Corina

Yeah, I need to close the input reader. Thanks for pointing out:) – Izy

Answer 4

I think XSLT and SAX could be a solution.

If you'll work with Stream that STaX is solution, I read Sun tutorial, I think is very helpful: Sun Tutorail on STaX

Bye

Keir

And if you decide to use Stax, make sure you use a good implementation (Woodstox). Also, StaxMate (wiki.fasterxml.com/StaxMateHome) can make Stax usage much simpler. – Corina

Answer 5

Check XmlCombiner which is a Java library that implements XML merging in exactly this way. It is loosely based on a similar functionality offered by plexus-utils library.

In your case the tags should be also matched based on the value of the attribute 'TestCaseID'. Here is the full example:

import org.atteo.xmlcombiner.XmlCombiner;

// create combiner
XmlCombiner combiner = new XmlCombiner("TestCaseID");
// combine files
combiner.combine(firstFile);
combiner.combine(secondFile);
// store the result
combiner.buildDocument(resultFile);

Disclaimer: I am the author of the library.

Finedraw

Answer 6

You can consider XML as text file and combine them. That is very fast as compared to other methods. Please have a look at below code :-

import java.io.*;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class XmlComb {

    static Set<String> lstheader = new HashSet<String>();

    public static void main(String[] args) throws IOException {
        Map<String,List<String>> map1 = getMapXml("J:\\Users\\Documents\\XMLCombiner01\\src\\main\\resources\\File1.xml");
        Map<String,List<String>> map2 = getMapXml("J:\\Users\\Documents\\XMLCombiner01\\src\\main\\resources\\File2.xml");
        Map<String,List<String>> mapCombined = combineXML(map1, map2);

        lstheader.forEach( lst -> {
            System.out.println(lst);
        });

        try {
            mapCombined.forEach((k,v) -> {

                System.out.println(k);
                v.forEach(val -> System.out.println(val));


            });
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public static Map<String,List<String>> combineXML(Map<String, List<String>> map1, Map<String, List<String>> map2 ) {

        Map<String,List<String>> map2Modified = new TreeMap<String, List<String>>();
        Map<String,List<String>> mapCombined = new TreeMap<String, List<String>>();
        // --- Modifying map ---
            for(String strKey2 : map2.keySet()) {

                if(map1.containsKey(strKey2)) {
                    map2Modified.put(strKey2.split("\">")[0] + "_1\">", map2.get(strKey2));
                }
                else {
                    map2Modified.put(strKey2 , map2.get(strKey2));
                }
            }   

            //---- Combining map ---

            map1.putAll(map2Modified);

            return map1;
    }


     public static Map<String,List<String>> getMapXml(String strFilePath) throws IOException{
         File file = new File(strFilePath);

        BufferedReader br = new BufferedReader(new FileReader(file));
        Map<String, List<String>> testMap = new TreeMap<String, List<String>>();
        List<String> lst = null;

        String st;
        String strCatalogName = null;
        while ((st = br.readLine()) != null) {
            //System.out.println(st);
            if(st.toString().contains("<TestCase")){
                lst = new ArrayList<String>();
                strCatalogName = st;
                testMap.put(strCatalogName, lst);
            }
            else if(st.contains("</TestCase")){
                lst.add(st);
                testMap.put(strCatalogName,lst);
            }
            else {
                if(lst != null){
                    lst.add(st);
                }else {
                    lstheader.add(st);
                }

            }

        }

        return testMap;
    }
}

Tracheitis