How to Generate an XML File from a set of XPath Expressions?

Question

I want to be able to generate a complete XML file, given a set of XPath mappings.

The input could specified in two mappings: (1) One which lists the XPath expressions and values; and (2) the other which defines the appropriate namespaces.

/create/article[1]/id                 => 1
/create/article[1]/description        => bar
/create/article[1]/name[1]            => foo
/create/article[1]/price[1]/amount    => 00.00
/create/article[1]/price[1]/currency  => USD
/create/article[2]/id                 => 2
/create/article[2]/description        => some name
/create/article[2]/name[1]            => some description
/create/article[2]/price[1]/amount    => 00.01
/create/article[2]/price[1]/currency  => USD

For namespaces:

/create               => xmlns:ns1='http://predic8.com/wsdl/material/ArticleService/1/
/create/article       => xmlns:ns1='http://predic8.com/material/1/‘
/create/article/price => xmlns:ns1='http://predic8.com/common/1/‘
/create/article/id    => xmlns:ns1='http://predic8.com/material/1/'

Note also, that it is important that I also deal with XPath Attributes expressions as well. For example: I should also be able to handle attributes, such as:

/create/article/@type => richtext

The final output should then look something like:

<ns1:create xmlns:ns1='http://predic8.com/wsdl/material/ArticleService/1/'>
    <ns1:article xmlns:ns1='http://predic8.com/material/1/‘ type='richtext'>
        <name>foo</name>
        <description>bar</description>
        <ns1:price xmlns:ns1='http://predic8.com/common/1/'>
            <amount>00.00</amount>
            <currency>USD</currency>
        </ns1:price>
        <ns1:id xmlns:ns1='http://predic8.com/material/1/'>1</ns1:id>
    </ns1:article>
    <ns1:article xmlns:ns1='http://predic8.com/material/2/‘ type='richtext'>
        <name>some name</name>
        <description>some description</description>
        <ns1:price xmlns:ns1='http://predic8.com/common/2/'>
            <amount>00.01</amount>
            <currency>USD</currency>
        </ns1:price>
        <ns1:id xmlns:ns1='http://predic8.com/material/2/'>2</ns1:id>
    </ns1:article>
</ns1:create>

PS: This is a more detailed question to a previous question asked, although due to a series of further requirements and clarifications, I was recommended to ask a more broader question in order to address my needs.

Note also, I am implementing this in Java. So either a Java-based or XSLT-based solution would both be perfectly acceptable. thnx.

Further note: I am really looking for a generic solution. The XML shown above is just an example.

Answer 1

i came across a similar situation where i had to convert Set of XPath/FQN - value mappings to XML. A generic simple solution can be using the following code, which can be enhanced to specific requirements.

public class XMLUtils {
static public String transformToXML(Map<String, String> pathValueMap, String delimiter)
        throws ParserConfigurationException, TransformerException {

    DocumentBuilderFactory documentFactory = DocumentBuilderFactory.newInstance();
    DocumentBuilder documentBuilder = documentFactory.newDocumentBuilder();
    Document document = documentBuilder.newDocument();

    Element rootElement = null;

    Iterator<Entry<String, String>> it = pathValueMap.entrySet().iterator();
    while (it.hasNext()) {
        Entry<String, String> pair = it.next();
        if (pair.getKey() != null && pair.getKey() != "" && rootElement == null) {
            String[] pathValuesplit = pair.getKey().split(delimiter);
            rootElement = document.createElement(pathValuesplit[0]);
            break;
        }
    }

    document.appendChild(rootElement);
    Element rootNode = rootElement;
    Iterator<Entry<String, String>> iterator = pathValueMap.entrySet().iterator();
    while (iterator.hasNext()) {
        Entry<String, String> pair = iterator.next();
        if (pair.getKey() != null && pair.getKey() != "" && rootElement != null) {
            String[] pathValuesplit = pair.getKey().split(delimiter);
            if (pathValuesplit[0].equals(rootElement.getNodeName())) {
                int i = pathValuesplit.length;

                Element parentNode = rootNode;
                int j = 1;

                while (j < i) {
                    Element child = null;

                    NodeList childNodes = parentNode.getChildNodes();
                    for (int k = 0; k < childNodes.getLength(); k++) {
                        if (childNodes.item(k).getNodeName().equals(pathValuesplit[j])
                                && childNodes.item(k) instanceof Element) {
                            child = (Element) childNodes.item(k);
                            break;
                        }
                    }

                    if (child == null) {
                        child = document.createElement(pathValuesplit[j]);
                        if (j == (i - 1)) {
                            child.appendChild(
                                    document.createTextNode(pair.getValue() == null ? "" : pair.getValue()));
                        }
                    }
                    parentNode.appendChild(child);
                    parentNode = child;
                    j++;
                }
            } else {
                // ignore any other root - add logger
                System.out.println("Data not processed for node: " + pair.getKey());
            }
        }
    }

    TransformerFactory transformerFactory = TransformerFactory.newInstance();
    Transformer transformer = transformerFactory.newTransformer();
    DOMSource domSource = new DOMSource(document);

    // to return a XMLstring in response to an API
     StringWriter writer = new StringWriter();
     StreamResult result = new StreamResult(writer);

     StreamResult resultToFile = new StreamResult(new File("C:/EclipseProgramOutputs/GeneratedXMLFromPathValue.xml"));
     transformer.transform(domSource, resultToFile);
     transformer.transform(domSource, result);

    return writer.toString();
}

public static void main(String args[])
{

    Map<String, String> pathValueMap = new HashMap<String, String>();
    String delimiter = "/";

    pathValueMap.put("create/article__1/id", "1");
    pathValueMap.put("create/article__1/description", "something");
    pathValueMap.put("create/article__1/name", "Book Name");
    pathValueMap.put("create/article__1/price/amount", "120" );
    pathValueMap.put("create/article__1/price/currency", "INR");
    pathValueMap.put("create/article__2/id", "2");
    pathValueMap.put("create/article__2/description", "something else");
    pathValueMap.put("create/article__2/name", "Book name 1");
    pathValueMap.put("create/article__2/price/amount", "2100");
    pathValueMap.put("create/article__2/price/currency", "USD");

    try {
        XMLUtils.transformToXML(pathValueMap, delimiter);
    } catch (ParserConfigurationException | TransformerException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}}

Output:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<create>
    <article__1>
        <id>1</id>
    <name>Book Name</name>
    <description>something</description>
    <price>
        <currency>INR</currency>
        <amount>120</amount>
    </price>
</article__1>
<article__2>
    <description>something else</description>
    <name>Book name 1</name>
    <id>2</id>
    <price>
        <currency>USD</currency>
        <amount>2100</amount>
    </price>
</article__2>

To remove __%num , can use regular expressions on final string. like:

resultString = resultString.replaceAll("(__[0-9][0-9])|(__[0-9])", "");

This would do the cleaning job

Answer 2

This problem has an easy solution if one builds upon the solution of the previous problem:

<xsl:stylesheet version="2.0"
     xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:my="my:my">
     <xsl:output omit-xml-declaration="yes" indent="yes"/>

     <xsl:key name="kNSFor" match="namespace" use="@of"/>
     <xsl:variable name="vStylesheet" select="document('')"/>

     <xsl:variable name="vPop" as="element()*">
        <item path="/create/article/@type">richtext</item>
        <item path="/create/article/@lang">en-us</item>
        <item path="/create/article[1]/id">1</item>
        <item path="/create/article[1]/description">bar</item>
        <item path="/create/article[1]/name[1]">foo</item>
        <item path="/create/article[1]/price[1]/amount">00.00</item>
        <item path="/create/article[1]/price[1]/currency">USD</item>
        <item path="/create/article[1]/price[2]/amount">11.11</item>
        <item path="/create/article[1]/price[2]/currency">AUD</item>
        <item path="/create/article[2]/id">2</item>
        <item path="/create/article[2]/description">some name</item>
        <item path="/create/article[2]/name[1]">some description</item>
        <item path="/create/article[2]/price[1]/amount">00.01</item>
        <item path="/create/article[2]/price[1]/currency">USD</item>

        <namespace of="create" prefix="ns1:"
                   url="http://predic8.com/wsdl/material/ArticleService/1/"/>
        <namespace of="article" prefix="ns1:"
                   url="xmlns:ns1='http://predic8.com/material/1/"/>
        <namespace of="@lang" prefix="xml:"
                   url="http://www.w3.org/XML/1998/namespace"/>
        <namespace of="price" prefix="ns1:"
                   url="xmlns:ns1='http://predic8.com/material/1/"/>
        <namespace of="id" prefix="ns1:"
                   url="xmlns:ns1='http://predic8.com/material/1/"/>
     </xsl:variable>

     <xsl:template match="/">
      <xsl:sequence select="my:subTree($vPop/@path/concat(.,'/',string(..)))"/>
     </xsl:template>

     <xsl:function name="my:subTree" as="node()*">
      <xsl:param name="pPaths" as="xs:string*"/>

      <xsl:for-each-group select="$pPaths" group-adjacent=
            "substring-before(substring-after(concat(., '/'), '/'), '/')">
        <xsl:if test="current-grouping-key()">
         <xsl:choose>
           <xsl:when test=
              "substring-after(current-group()[1], current-grouping-key())">

             <xsl:variable name="vLocal-name" select=
              "substring-before(concat(current-grouping-key(), '['), '[')"/>

             <xsl:variable name="vNamespace"
                           select="key('kNSFor', $vLocal-name, $vStylesheet)"/>


             <xsl:choose>
              <xsl:when test="starts-with($vLocal-name, '@')">
               <xsl:attribute name=
                 "{$vNamespace/@prefix}{substring($vLocal-name,2)}"
                    namespace="{$vNamespace/@url}">
                 <xsl:value-of select=
                  "substring(
                       substring-after(current-group(), current-grouping-key()),
                       2
                             )"/>
               </xsl:attribute>
              </xsl:when>
              <xsl:otherwise>
               <xsl:element name="{$vNamespace/@prefix}{$vLocal-name}"
                          namespace="{$vNamespace/@url}">

                    <xsl:sequence select=
                     "my:subTree(for $s in current-group()
                                  return
                                     concat('/',substring-after(substring($s, 2),'/'))
                                   )
                     "/>
                 </xsl:element>
              </xsl:otherwise>
             </xsl:choose>
           </xsl:when>
           <xsl:otherwise>
            <xsl:value-of select="current-grouping-key()"/>
           </xsl:otherwise>
         </xsl:choose>
         </xsl:if>
      </xsl:for-each-group>
     </xsl:function>
</xsl:stylesheet>

When this transformation is applied on any XML document (not used), the wanted, correct result is produced:

<ns1:create xmlns:ns1="http://predic8.com/wsdl/material/ArticleService/1/">
   <ns1:article xmlns:ns1="xmlns:ns1='http://predic8.com/material/1/" type="richtext"
                xml:lang="en-us"/>
   <ns1:article xmlns:ns1="xmlns:ns1='http://predic8.com/material/1/">
      <ns1:id>1</ns1:id>
      <description>bar</description>
      <name>foo</name>
      <ns1:price>
         <amount>00.00</amount>
         <currency>USD</currency>
      </ns1:price>
      <ns1:price>
         <amount>11.11</amount>
         <currency>AUD</currency>
      </ns1:price>
   </ns1:article>
   <ns1:article xmlns:ns1="xmlns:ns1='http://predic8.com/material/1/">
      <ns1:id>2</ns1:id>
      <description>some name</description>
      <name>some description</name>
      <ns1:price>
         <amount>00.01</amount>
         <currency>USD</currency>
      </ns1:price>
   </ns1:article>
</ns1:create>

Explanation:

1. A reasonable assumption is made that throughout the generated document any two elements with the same local-name() belong to the same namespace -- this covers the predominant majority of real-world XML documents.

2. The namespace specifications follow the path specifications. A nsmespace specification has the form: <namespace of="target element's local-name" prefix="wanted prefix" url="namespace-uri"/>

3. Before generating an element with xsl:element, the appropriate namespace specification is selected using an index created by an xsl:key. From this namespace specification the values of its prefix and url attributes are used in specifying in the xsl:element instruction the values of the full element name and the element's namespace-uri.

Answer 3

Interesting question. Let's assume that your input set of XPath expressions satisfies some reasonsable constraints, for example if there is an X/article[2] then there also (preceding it) an X/article[1]. And let's put the namespace part of the problem to one side for the moment.

Let's go for an XSLT 2.0 solution: we'll start with the input in the form

<paths>
<path value="1">/create/article[1]/id</path>
<path value="bar">/create/article[1]/description</path>
</paths>

and then we'll turn this into

<paths>
<path value="1"><step>create</step><step>article[1]</step><step>id</step></path>
   ...
</paths>

Now we'll call a function which does a grouping on the first step, and calls itself recursively to do grouping on the next step:

<xsl:function name="f:group">
  <xsl:param name="paths" as="element(path)*"/>
  <xsl:param name="step" as="xs:integer"/>
  <xsl:for-each-group select="$paths" group-by="step[$step]">
    <xsl:element name="{replace(current-grouping-key(), '\[.*', '')}">
      <xsl:choose>
        <xsl:when test="count(current-group) gt 1">
           <xsl:sequence select="f:group(current-group(), $step+1)"/>
        </xsl:when>
        <xsl:otherwise>
           <xsl:value-of select="current-group()[1]/@value"/>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:element>
  </xsl:for-each-group>
</xsl:function>

That's untested, and there may well be details you have to adjust to get it working. But I think the basic approach should work.

The namespace part of the problem is perhaps best tackled by preprocessing the list of paths to add a namespace attribute to each step element; this can then be used in the xsl:element instruction to put the element in the right namespace.