Limit XML SAXParser to certain number or item

Question

I am parsing an rss XML news feed for an Android app. I am using SAXParser and all is working as it should but I would like to be able to limit the number of stories that I am retrieving and I cannot find a way to do so. For instance, say there are 45 stories from one of the news feeds and I just want the newest 10. As it is now, I am just grabbing them all into an ArrayList and only displaying the ones I want, which most certainly is the most efficient way of doing this I am sure.

I can provide the parsing code if necessary.

Thanks to anyone looking at this!

When you are adding objects to arraylist simply check its size and don't add to it if it has 10 elements. — Misagh Emamverdi, Sep 28 '14 at 06:24
I thought about that but that would mean that the entire XML will still get parsed. I would rather simply stop parsing once the `ArrayList` gets to the desired size. — WeVie, Sep 28 '14 at 06:26
You could just break out/return from the parsing operation after hitting the desired number of elements (or until there are no more to process, whichever comes first)? — MH., Sep 28 '14 at 06:37
How so @MH. ? Will a simple `break` work if I add a counter to the `startElement()` method where I am adding objects to the list? — WeVie, Sep 28 '14 at 06:41
Sorry, that comment was a little inaccurate: a break or return won't work. You'll have to throw an exception, as suggested [here](http://www.ibm.com/developerworks/library/x-tipsaxstop/). A quick search on SO yields the same answer. Not the prettiest, but functional, I suppose... Have a look at the [accepted answer here](http://stackoverflow.com/questions/1345293/how-to-stop-parsing-xml-document-with-sax-at-any-time) for some concrete pointers. — MH., Sep 28 '14 at 07:03

score 2 · Answer 1 · answered Sep 28 '14 at 09:35

2

You can stop a SAX parser from parsing any more input by having any of your callback methods (e.g. startElement) throw a SAXException.

You will need to make this exception recognizable (e.g. by using special message text, or by using a subclass of SAXException) so that when your original call of parse() comes back with an exception, you can distinguish it from other causes of parser failure.

answered Sep 28 '14 at 09:35

Michael Kay

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Do you have an example of how to do this? – WeVie Sep 28 '14 at 14:12
Not a simple one, I'm afraid. There's an example of the general technique at http://grepcode.com/file/repo1.maven.org/maven2/net.sourceforge.saxon/saxon/9.1.0.8/net/sf/saxon/event/PIGrabber.java, but it's not using SAX interfaces directly, so the events and exceptions are slightly different. (This example is to read the xml-stylesheet processing instruction at the start of a file, and then abort the parse when the first element node is encountered.) – Michael Kay Sep 28 '14 at 20:39

Misagh Emamverdi · Answer 2 · 2014-09-28T18:49:40.373

I am not sure that there is a way to stop sax parser from parsing. However you can use XMLPullParser instead.

XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
XmlPullParser xpp = factory.newPullParser();
xpp.setInput(yourXML);

int eventType = xpp.getEventType();

while (eventType != XmlPullParser.END_DOCUMENT && list.size() <= MAX_SIZE) {

    if (eventType == XmlPullParser.START_TAG) {
        //do something
    } else if (eventType == XmlPullParser.END_TAG) {
        //do something
    } else if (eventType == XmlPullParser.TEXT) {
        //do something
    }
    eventType = xpp.next();
}

You can find lots of examples by searching XMLPullParser tutorial.

Note: I think in case you have just 45 items parsing is very fast and you can let sax to continue parsing.

Update: I think it is what Michael says:

@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {

   if(size == MAX_SIZE){
      throw new SAXException("end");
    }
    //...
 }

And when you are parsing:

try{
saxParser.parse(yourXML);
}catch(SAXException e){
  if(e.getMessage().equals("end"){
    // document has ended
  }
}

I just used 45 as an example. What if there are hundreds? It's not so fast anymore. I am aware of PullParser but need to learn more about SAX. — WeVie, Sep 28 '14 at 14:16

Limit XML SAXParser to certain number or item

2 Answers2