Question

So I have a project where I need to pull an xml file that is updated every 5 minutes. However I’m designing my program to pull this file every time it updates.

The data structure of the xml file is like this…

<m:REPORT_DATA>
    <m:DATA_ITEM>ENC</m:DATA_ITEM>
    <m:RESOURCE_NAME>DLAP</m:RESOURCE_NAME>
    <m:OPR_DATE>2012-06-02</m:OPR_DATE>
    <m:INTERVAL_NUM>1</m:INTERVAL_NUM>
    <m:VALUE>16.77734</m:VALUE>
</m:REPORT_DATA>
<m:REPORT_DATA>
    <m:DATA_ITEM>ENC</m:DATA_ITEM>
    <m:RESOURCE_NAME>DLAP</m:RESOURCE_NAME>
    <m:DATE>2012-06-02</m:OPR_DATE>
    <m:INTERVAL_NUM>2</m:INTERVAL_NUM>
    <m:VALUE>16.77739</m:VALUE>
</m:REPORT_DATA>
....

Assuming that I pull it for the 200th time that day, how would I grab just the last value

"<m:VALUE>16.77739</m:VALUE>"

And get that value for my database?

I’m torn about using Sax, Xpath, or DOM. Some help would be amazing.

Answer 1

If you had a root, lets say <m:REPORTS>, finding the last VALUE using XPath would be rather simple:

    XPathFactory f = XPathFactory.newInstance() ;
    XPath x = f.newXPath() ;
    try {
        InputSource source = new InputSource(new FileInputStream("logfile.xml")) ;
        XPathExpression expr = x.compile("//REPORT_DATA[DATA_ITEM='ENC'][last()]/VALUE/text()") ;
        String s = expr.evaluate(source) ;
        System.out.println("Last value: " + s ) ;
    }
    catch(Throwable t) {
        System.err.println("Error: " + t) ;
    }