XPath: generate a relative expression from a root node to a specified node?

How can I generate the required XPath expression to traverse from a given root node to a specified node down the xml structure?

I will receive HTML fragment of a table at runtime. I have to find the desired node based on some criteria and the for开发者_JS百科m an XPath string from the table root node to that node and return that.

The HTML table structure is not known beforehand. Is there any API in Java that returns the XPath string given the root node and the child node?

I would recommend doing this in Groovy which provides GPATH (essentially an xpath implementation for the groovy language.) The Groovy syntax is very succint and powerful as described in my blog and mixes seamlessly with the he Java language (groovy is compiled down to java class files).

As for what you are trying to achieve...the following should traverse the entire HTML DOM structure and search for a "tag" (e.g. div) with a specific id attribute (e.g. unique_id_for_tag) with each entry found to be processed by the closure.

HTML.body.'**'.findAll {  it.name() == 'tag' && it["@id"] == 'tag_name' }.each { 
//"it" is the return value
if(it.td[0].text().toString().trim().contains('Hello')){
   var x = it.td[0].text().toString().trim();
}

Below is one way (that I know) to achieve this

1. Create a DOM of XML
2. Get the Node of the specified node using the "//" XPATH
3. Once you have the Node object from step 2 then it is just a matter of traversing up hierarchy using getParentNode() and building the xpath

This cannot be done (only) in pure XPath 1.0.

XPath 2.0 solution:

if(not($vStart intersect $vTarget/ancestor::*))
  then ()
  else
   for $vPath in
      string-join
          ((for $x in
                $vTarget
                  /ancestor-or-self::*[. >> $vStart]
                    /concat(name(.),
                            for $n in name(.),
                                $cn in count(../*[name(.) eq $n])
                             return
                               if($cn ge 2)
                                 then concat('[', 
                                               count((preceding-sibling::*
                                                              [name() eq $n]) +1, 
                                             ']')
                                 else (),
                            '/'
                               )
               return $x),
              ''
           )
           return string-join((concat(name($vStart), '/'),$vPath), '')

When this XPath 2.0 expression is evaluated against the following XML document:

<table>
  <tr>
    <td><b>11</b></td>
    <td><i>12</i></td>
  </tr>
  <tr>
    <td><p><b>21</b></p></td>
    <td><p><b>221</b></p><p><b><i>222</i></b></p></td>
  </tr>
  <tr>
    <td><b>31</b></td>
    <td><i>32</i></td>
  </tr>
</table>

and if the two parameters are defined as:

  <xsl:variable name="vStart" select="/*"/>
  <xsl:variable name="vTarget" select="/*/tr[2]/td[2]/p[2]/b/i"/>

then the result of the evaluation of the XPath 2.0 expression above is:

table/tr[2]/td[2]/p[2]/b/i/

If you know the names of the root element and the child element you are trying to select, and if there is only one child element with that name, you could use simply "/root//child". But maybe I misunderstood what you were trying to achieve. Could you give an example ?