Java VTD-XML and XPath: Use XPath in found section

Question

I have the following XML File:

<project>
    <category type="Files">
        <type name="File" type="String" id="1">
            <field name="Name" type="String">
                <value type="String"><![CDATA[Smile.JPG]]></value>
            </field>
            <multiValue name="Entries" type="FileEntry">
                <model type="Specs" state="Intact">
                    <field name="Value" type="String">
                        <value type="String"><![CDATA[10241624]]></value>
                    </field>
                  </model>
            </multiValue>
        </type>
        <type name="File" type="String" id="2">
            <field name="Name" type="String">
                <value type="String"><![CDATA[OldMan.JPG]]></value>
            </field>
            <multiValue name="Entries" type="FileEntry">
                <model type="Specs" state="Gone">
                    <field name="Category" type="String">
                        <value type="String"><![CDATA[Size]]></value>
                    </field>
                    <field name="Value" type="String">
                        <value type="String"><![CDATA[821563412]]></value>
                    </field>
                </model>
            </multiValue>
        </type>
    </category>
</project>

java code snippet: (Just the code to isolate the issue)

VTDGen vg = new VTDGen();
int i;
AutoPilot ap = new AutoPilot();
ap.selectXPath("/project/category[@type=\"Files\"]");
AutoPilot ap2 = new AutoPilot();
BookMark bm = new BookMark();

vg.parseFile("stackoverflow_example.xml", false);

VTDNav vn = vg.getNav();
ap.bind(vn);
ap2.bind(vn);

/* main XPath selection */
ap.selectXPath("/project/category[@type=\"Files\"]");

/* part 1 */
//XPath eval returns one node at a time
ap2.selectXPath("type[@name=\"File\"]/field/value/text()");
while ((i = ap.evalXPath()) != -1) {
    bm.recordCursorPosition(); // equivalent to vn.push();
    int j;
    while ((j = ap2.evalXPath()) != -1) {
            logger.debug(" NAME ==> " + vn.toString(j));
    }
    ap2.resetXPath();
    bm.setCursorPosition(); // equivalent to vn.pop();
}
ap.resetXPath();

/* part 2 */
ap2.selectXPath("type[@name=\"File\"]/multiValue/model[@type=\"Specs\"]/field[@name=\"Value\"]/value/text()");
while ((i = ap.evalXPath()) != -1) {
    bm.recordCursorPosition(); // equivalent to vn.push();
    int j;
    while ((j = ap2.evalXPath()) != -1) {
        logger.debug(" SIZE ==> " + vn.toString(j));
    }
    ap2.resetXPath();
    bm.setCursorPosition(); // equivalent to vn.pop();
}
ap.resetXPath();

And after finding one section of the type with the name File, I want to get the filename and size from this section. (Of course, later on a bit more, but for my understanding, this would be sufficient).

The problem with the code is now, that it does find the matching values, but the SIZE is not a child from the File.

Output:

NAME ==> Smile.JPG
NAME ==> OldMan.JPG

SIZE ==> 10241624
SIZE ==> 821563412

I have two AutoPilots, one for the main section and I had the idea to inner-search with the second AutoPilot.

Can anybody help only "search" in the first found section? I would like to have some output like:

NAME ==> Smile.JPG
SIZE ==> 10241624

NAME ==> OldMan.JPG
SIZE ==> 821563412

Answer 1

Your sample code has at least 2 issues IMO, at least in my understanding of VTD-XML. First, the xpath queries for the file name and size seem strange to me as they don't contain a root like / or //. Next, it would be preferrable to extract the file-id's and add them to the XPath queries.

I took your code and tweaked it a bit

import com.ximpleware.AutoPilot;
import com.ximpleware.VTDGen;
import com.ximpleware.VTDNav;
import java.io.File;
import java.lang.invoke.MethodHandles;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class StackOverflowExample {

  private static final Logger LOG = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());

  public static void main(String ... args) throws Exception {
    VTDGen vg = new VTDGen();

    File testFile = new File(StackOverflowExample.class.getResource("/stackoverflow_example.xml").toURI());
    vg.parseFile(testFile.getAbsolutePath(), false);

    VTDNav vn = vg.getNav();
    AutoPilot ap = new AutoPilot();
    ap.bind(vn);
    AutoPilot ap2 = new AutoPilot();
    ap2.bind(vn);

    // iterate over all file IDs
    int i;
    ap.selectXPath("//category[@type=\"Files\"]/type/@id");
    while ((i = ap.evalXPath()) != -1) {
      int j;

      // retrieve the value of the id attribute field
      String attributeName = vn.toString(i);
      int attributeId = vn.getAttrVal(attributeName);
      String attributeVal = vn.toString(attributeId);

      // add the id value to the respective xpath query
      ap2.selectXPath("//category[@type=\"Files\"]/type[@name=\"File\" and @id=\"" + attributeVal + "\"]/field/value/text()");
      while ((j = ap2.evalXPath()) != -1) {
        LOG.debug(" NAME ==> " + vn.toString(j));
      }
      ap2.resetXPath();

      ap2.selectXPath("//category[@type=\"Files\"]/type[@name=\"File\" and @id=\"" + attributeVal + "\"]/multiValue/model[@type=\"Specs\"]/field[@name=\"Value\"]/value/text()");
      while ((j = ap2.evalXPath()) != -1) {
        LOG.debug(" SIZE ==> " + vn.toString(j));
      }
      ap2.resetXPath();
    }
    ap.resetXPath();
  }
}

which produces the following output

11:57:07.196 [main] DEBUG StackOverflowExample -  NAME ==> Smile.JPG
11:57:07.201 [main] DEBUG StackOverflowExample -  SIZE ==> 10241624
11:57:07.202 [main] DEBUG StackOverflowExample -  NAME ==> OldMan.JPG
11:57:07.204 [main] DEBUG StackOverflowExample -  SIZE ==> 821563412

Note that if you use an XPath query like /project/category[@type="Files"]/type/@id instead of //category[@type="Files"]/type/@id only the first value file element will be listed. Not sure why VTD-XML does not iterate over all the elements.