Attempt to get next and previous sibling of a node after parsing xml for a specific node using java

Question

I have an xml containing the log of 1000 events where each one has a key, My objective is when a user search for an event key, i should display him the xml of the event node having this key and prepare the info of the previous and next sibling.

The xml structure is as follow:

<LOG>
   <EVENT_SET>
      <DOCGET system="T610_00" fingerPrint="NO_SIGNATURE">
         <event>
            <key>382</key>
            <date>2015-01-28T09:15:15.350+0000</date>
            <service>CORE</service>
            <class>APPLICATION</class>
         </event>
         <document>
            <docuri>getdocs:///DocMapCSDOCS.dPortal/1</docuri>
            <sign_info>
               <signature>VqtR9Gpny/MPE43/5o4hJXp8bR7gbsVUJqHlTI+VfztMSQecTpZwAQpxmorrdBJKvmn+h7eZzV1geVodkVECvOjQMRmRbnpT6mrpbiXxjDOsZsQRDNemTYUKETrQFIBRtXcjoP61une1LOsS5C749ehwbZ1jEaNH6fPjH4n+OH4=</signature>
            </sign_info>
         </document>
      </DOCGET>
      <DOCGET system="T610_00" fingerPrint="NO_SIGNATURE">
         <event>
            <key>383</key>
            <date>2015-01-28T09:15:18.310+0000</date>
            <service>CORE</service>
            <class>APPLICATION</class>
         </event>
         <document>
            <docuri>getdocs:///DocMapCSDOCS.dPortal/2</docuri>
            <sign_info>
               <signature>VqtR9Gpny/MPE43/5o4hJXp8bR7gbsVUJqHlTI+VfztMSQecTpZwAQpxmorrdBJKvmn+h7eZzV1geVodkVECvOjQMRmRbnpT6mrpbiXxjDOsZsQRDNemTYUKETrQFIBRtXcjoP61une1LOsS5C749ehwbZ1jEaNH6fPjH4n+OH4=</signature>
            </sign_info>
         </document>
      </DOCGET>
      .......
  </EVENT_SET>
</LOG>

And my code till now to get the node of a key is:

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(false);
DocumentBuilder builder = factory.newDocumentBuilder();
//parsing the xml file
journaldoc = builder.parse(journalFile);
XPathFactory xpathfactory = XPathFactory.newInstance();
XPath xpath = xpathfactory.newXPath();

//xpath to search for the event having the key requated by the user
String sXpath = "//DOCGET[event/key='"+eventkey+"']";
XPathExpression expr = xpath.compile(sXpath);
Object result = expr.evaluate(journaldoc, XPathConstants.NODE);
Node eventnode = (Node) result;

//return to the user the xml part with root DOCGET, and having the key requested
Document document = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Node copyNode = document.importNode(eventNode, true);
document.appendChild(copyNode);
DOMImplementationLS domImplementationLS = (DOMImplementationLS) document.getImplementation();
LSSerializer lsSerializer = domImplementationLS.createLSSerializer();
String xmlNode =  lsSerializer.writeToString(document);

Now i need to get the previous and next sibling of this node and get their keys in order to save them in a HashMap.

The problem is when doing eventnode.getPreviousSibling and eventnode.getNextSibling , i am getting corrupted info and i am not able to get the key of these events.

Does anyone has a better idea to do this?

Thank you, Karine

Answer 1

I think you are looking for the XPath axis preceding-sibling and following-sibling. These select all nodes at the same level, so if you just want the next neighbors, you need to add a predicate to select just the first: following-sibling::*[1]. But you want only event nodes and the event nodes are not directly siblins, but the <DOCGET> elements are. So from an event node you need to go up, find the next/previous sibling and go down again. This boils down to this expression: ../preceding-sibling::*[1]/event to be evaluated on an event node.

You can ease the task by using data projection (Disclosure: I'm affiliated with that project) to have a object oriented access to the events, but still decouple the Java code structure from the XML structure:

public class ReadEvents {

public interface Event {
    @XBRead("./key")
    String getKey();

    @XBRead("./date using yyyy-MM-dd'T'HH:mm:ss.SSSZ")
    Date getDate();

    @XBRead("../document/docuri")
    String getDocumentURI();

    @XBRead("../preceding-sibling::*[1]/event")
    Event getPreviousEvent();

    @XBRead("../following-sibling::*[1]/event")
    Event getNextEvent();
}

public static void main(String... args) {
    List<Event> allEvents = new XBProjector().io().url("res://log.xml").evalXPath("//event").asListOf(Event.class);
    for (Event event : allEvents) {
        System.out.print(event.getDate()+ ": Event " + event.getKey());
        if (event.getPreviousEvent() != null) {
            System.out.print(" previous event has key " + event.getPreviousEvent().getKey());
        }
        if (event.getNextEvent() != null) {
            System.out.print(" next event has key " + event.getNextEvent().getKey());
        }
        System.out.println();
    }
  }
}

For your example, this program prints out:

Wed Jan 28 10:15:15 CET 2015: Event 382 next event has key 383
Wed Jan 28 10:15:18 CET 2015: Event 383 previous event has key 382