Question

I want to create a class to parse XML.
Here is my code :

public class ParserXML {

private String Flux;
private ArrayList<String> EvaluateExpr = new ArrayList<String>();
private ArrayList<String> Result  = new ArrayList<String>();

public ParserXML(String url, ArrayList<String> exp) {
    this.Flux = url;
    this.EvaluateExpr = exp;

    this.loadXmlFlux();
}

private void loadXmlFlux() {

    HttpClient httpclient = null;

    try {
        httpclient = new DefaultHttpClient();
        HttpGet httpget = new HttpGet(this.Flux);

        ResponseHandler<String> responseHandler = new BasicResponseHandler();
        String responseBody = httpclient.execute(httpget, responseHandler);

        InputSource docXml = new InputSource(new StringReader(responseBody)); 

        XPathFactory xpathFactory = XPathFactory.newInstance();

        XPath xpath = xpathFactory.newXPath();

        ArrayList<String> result = new ArrayList<String>();

        /*
         * Looping on all expression to evaluate
         */
        for (String i : this.EvaluateExpr) {
            try {
                result.add(xpath.evaluate(i, docXml));
            } catch (XPathExpressionException e) {
                e.printStackTrace();
            }

        }

        this.Result = result;

    } catch (HttpResponseException ex) {        
        ex.printStackTrace();
    }
    catch (IOException ex) {
       ex.printStackTrace();
    }   
    finally{
        if(httpclient!=null) {
            httpclient.getConnectionManager().shutdown();
        }
    }
}

public ArrayList<String> getResult() {
    return this.Result;
}

}

This class working fine when I’ve only one expression to evaluate.
But if I want to evaluate 2 expression on the XML stream I’ve error.

java.io.IOException: Stream closed
at java.io.StringReader.ensureOpen(Unknown Source)
at java.io.StringReader.read(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.load(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.arrangeCapacity(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.skipString(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLVersionDetector.determineDocVersion(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(Unknown Source)
at Common.ParserXML.loadXmlFlux(ParserXML.java:56)
at Common.ParserXML.(ParserXML.java:29)
at Domaine.Ahref.loadReferringDomains(Ahref.java:46)
at Domaine.Ahref.(Ahref.java:19)
at MainApp.checkAhrefs(MainApp.java:199)
at MainApp.main(MainApp.java:67)
————— linked to ——————
javax.xml.xpath.XPathExpressionException
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(Unknown Source)
at com.sun.org.apache.xpath.internal.jaxp.XPathImpl.evaluate(Unknown Source)
at Common.ParserXML.loadXmlFlux(ParserXML.java:56)
at Common.ParserXML.(ParserXML.java:29)
at Domaine.Ahref.loadReferringDomains(Ahref.java:46)
at Domaine.Ahref.(Ahref.java:19)
at MainApp.checkAhrefs(MainApp.java:199)
at MainApp.main(MainApp.java:67)
Caused by: java.io.IOException: Stream closed
at java.io.StringReader.ensureOpen(Unknown Source)
at java.io.StringReader.read(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.load(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.arrangeCapacity(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLEntityScanner.skipString(Unknown Source)
at com.sun.org.apache.xerces.internal.impl.XMLVersionDetector.determineDocVersion(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.parsers.DOMParser.parse(Unknown Source)
at com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderImpl.parse(Unknown Source)

I don’t understand why I can’t use again the “xpath.evaluate(i, docXml)” in the loop.

Thanks

Answer 1

You’re using the same InputSource twice – and after that InputSource has read the input once, the input is exhausted.

The simplest approach is probably to create a new InputSource for each iteration, with a new StringReader each time. Basically move this line:

InputSource docXml = new InputSource(new StringReader(responseBody)); 

into the loop.

Alternatively, I’m sure there must be a way of evaluating an XPath expression against a parsed DOM representation (e.g. Document) but I haven’t done enough Java XML work recently to know the relevant magic incantations. That would avoid having to reparse the XML for each expression though, which would obviously be nice.