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The next funny is that the XMLPullParser is responsible for everything else in the
parsing process, except providing information for a parsing problem, that's kindly left to
XMLPullException.:
XMLPullParser provides functions next() and nextToken()
to iterate over the XML data. next() only returns tags and text and skips everyting
else , whereas nextToken() faithfully reports processing instructions, entity declarations,
and comments.XMLPullParser provides access to the current XML token through various getter-functions:
for a token's name, namespace, prefix, text, and information on attributes. getEventType()
returns one of a number of constants detailing which kind of XML token was found. However, not all
functions work at the same time.The reason that the design of xmlpull ignores many principles used in the Java Standard and Enterprise Editions is simple, this API is designed for J2ME, the micro edition of Java. This means that:
XMLPullParserFactory
can do clever things behind the scenes to manage multiple XMLPullParsers simultaneously.XMLToken
class would have many instances created and waiting for garbage collection in one parsing process.Readers and Tokenizers is
less important because they are not part of J2ME.So this madness has a scheme behind it.
After so much destructive criticism let's focus on a constructive example. We want to count the maximal depth of nested elements in an XML document. To set up the parser, enter:
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
XmlPullParser parser = factory.newPullParser();
InputStream in = new FileInputStream(new File("blah.xml"));
parser.setInput(in, "ISO-8859-1"); // encoding can be set manually, use null for auto-detect
Ready, set, pull:
int maxdepth = 0;
int depth = 0;
for (int type = parser.next(); type != parser.END_DOCUMENT; type = parser.next()) {
if (type == XmlPullParser.START_TAG) {
depth++;
if (depth > maxdepth) {
maxdepth = depth;
}
}
else if (type == XmlPullParser.END_TAG) {
depth--;
}
}
After the parser has signalled END_DOCUMENT, maxdepth contains
the maximal nesting depth of XML nodes. Much less hassle than registering a callback interface with SAX's push model, or traversing document trees in DOM. In case you
forgot the details, you can easily review SAX and DOM.
An Application Programming Interface is only as good as its implementations. Two free packages exist:
Choosing to use these products in Micro-Java projects, as opposed to established SAX and DOM parsers, will decide the fate of this approach to XML parsing.
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URL: http://www.webreference.com/xml/column76/2.html
Created: Mar 03, 2003
Revised: Mar 03, 2003
