Search Strings in XML file using Stax

Question

I'm using stsx to search for strings "t_val_calc_pwr_consumed" & "t_val_calc_enrg_accumulated" in the xsd section under "rules" tag of an xml file. When i try to search in the rules section of each "ElementDefinitionModel" tag, i get a null pointer exception

XML file..

 <elementDefinitionModel manufacturerInSymbol="CARLO GAVAZZI" minSupportedVersionInSymbol="1.4" modelInSymbol="EM24-DIN_AV9_3_X_IS" modelQualifierInSymbol="EM24-DIN_AV9_3_X_IS" symbolTag="CARLO$GAVAZZIEM24-DIN_AV9_3_X_ISEM24-DIN_AV9_3_X_IS">
    <rules>
        <rule>
            <r:collection enabled="true" level_one_interval="5" level_two_interval="15" mode="normalMode" name="CollectionRule_t_val_calc_enrg_interval">
                <r:datapoint programmaticName="t_val_calc_enrg_interval" />
                <r:normal>
                    <r:currentValue interval="300" />
                </r:normal>
                <r:accelerated interval="30" />
                <r:computation formulaType="EnergyIntervalUsingAccEnergy" assignedDatapoint="t_val_calc_enrg_accumulated" formula="VAL(t_val_meter_enrg_phsA) VAL(t_val_meter_enrg_phsB) + VAL(t_val_meter_enrg_phsC) +" compFormula="VAL(t_val_meter_enrg_phsA) VAL(t_val_meter_enrg_phsB) + VAL(t_val_meter_enrg_phsC) +" />
                <r:aggregation>
                    <r:aggFunction>SUM</r:aggFunction>
                </r:aggregation>
            </r:collection>
        </rule>
        <rule>
            <r:collection enabled="true" level_one_interval="5" level_two_interval="15" mode="normalMode" name="CollectionRule_t_val_calc_pwr_consumed">
                <r:datapoint programmaticName="t_val_calc_pwr_consumed" />
                <r:normal>
                    <r:currentValue interval="300" />
                </r:normal>
                <r:accelerated interval="30" />
                <r:computation compFormula="VAL(t_val_meter_pwr_phsA) VAL(t_val_meter_pwr_phsB) + VAL(t_val_meter_pwr_phsC) +" formula="VAL(t_val_meter_pwr_phsA) VAL(t_val_meter_pwr_phsB) + VAL(t_val_meter_pwr_phsC) +" formulaType="ConsumedPower" />
            </r:collection>
        </rule>
        <rule>
            <r:analysis enabled="false" name="AnalysisRule_t_val_calc_pwr_consumed" source="Engine">
                <r:datapoint programmaticName="t_val_calc_pwr_consumed" />
                <r:parametricThreshold>
                    <r:highCritical eventProgrammaticName="t_evt_dp_genericThrshldHighCritical" />
                    <r:highWarning eventProgrammaticName="t_evt_dp_genericThrshldHighWarning" />
                    <r:lowWarning eventProgrammaticName="t_evt_dp_genericThrshldLowWarning" />
                    <r:lowCritical eventProgrammaticName="t_evt_dp_genericThrshldLowCritical" />
                </r:parametricThreshold>
            </r:analysis>
        </rule>
    </rules>
   </elementDefinitionModel>

Java code..

    public class PUE_Checker {

    public static void main(String[] args) throws XMLStreamException, ParserConfigurationException, SAXException, IOException{
    // TODO code application logic here
    Integer count =0;
    Integer x =0;
    Integer size;
    String PUE1;
    String model;
    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    org.w3c.dom.Document document = db.parse(new File("E:\\SVN\\R3.3\\DataDefinition\\file.xml"));
    NodeList nodeList = document.getElementsByTagName("r:datapoint");
    for(x=0,size= nodeList.getLength(); x<size; x++) {
         model= nodeList.item(x).getParentNode().getParentNode().getAttributes().getNamedItem("modelInSymbol").getNodeValue();
          if(model.length() > 0){
        PUE1 = nodeList.item(x).getAttributes().getNamedItem("programmaticName").getNodeValue();
        if("t_val_calc_pwr_consumed".equals(PUE1) || "t_val_calc_enrg_accumulated".equals(PUE1)){
       count++;
        }
       if(count==2){
         System.out.println("Points present in"+nodeList.item(x).getParentNode().getParentNode().getAttributes().getNamedItem("modelInSymbol").getNodeValue());
         }
         }
         }     
         }
         }

Expected output..

 Points present in EM24-DIN_AV9_3_X_IS

Current Output

     Exception in thread "main" java.lang.NullPointerException
 at sample.PUE_Checker.main(PUE_Checker.java:37)
 Java Result: 1

Edit 1:

The line referred to as "PUE_Checker.java:37" is

 model= nodeList.item(x).getParentNode().getParentNode().getAttributes().getNamedItem("modelInSymbol").getNodeValue();

Answer 1

The problem is that you try to find the attribute "modelInSymbol" in the "rule" tag. That leads to a NullPointerException. You could do this in two steps : - search for the attribute "modelInSymbol" in the root tag element - search for the attribute "programmaticName" in the "r:datapoint" and reuse the result of the preceding search.

In the way you do it, you search for "modelInSymbol" for every "r:datapoint". But there's only one.
So do it the first time and reuse it everytime you need it.

I did this in a text editor so may be it won't work, but it could be a hint :

Element rootElement = xmlDocument.getDocumentElement();
String modelInSymbol = rootElement.getAttribute("modelInSymbol");

NodeList nodeList = document.getElementsByTagName("r:datapoint");
for(x=0,size= nodeList.getLength(); x<size; x++) {
    if(modelInSymbol!= null && modelInSymbol.length() > 0){
        PUE1 = nodeList.item(x).getAttributes().getNamedItem("programmaticName").getNodeValue();
        if("t_val_calc_pwr_consumed".equals(PUE1) || "t_val_calc_enrg_accumulated".equals(PUE1)){
            count++;
        }
       if(count==2){
         System.out.println("Points present in"+modelInSymbol);
       }
    }
}