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XML processing is moving into the non-PC space, with PDAs and mobile phones acting as Web service clients and synchronizing their content with desktops via SyncML. Conserving heap and stack memory is a key requirement in this environment. With xmlpull, a new API has been devised for parsing XML.
What seems like a radically new idea is actually an evolution of a familiar
pattern in disguise, used in Java's input/output library. This author remembers when he implemented
his first XML parser, consisting of XMLReader, XMLToken and
XMLException, used like this:
XMLReader reader = new XMLReader(new FileReader("blah.xml"));
try {
while (reader.isAvailable()) {
XMLToken token = reader.read();
switch (token) {
case XMLTOKEN.START_TAG:
case XMLTOKEN.END_TAG:
case XMLTOKEN.TEXT:
// process token
}
}
}
catch (IOException ex) {
// something went wrong with the underlying file
}
catch (XMLException ex) {
// something is wrong with the XML (e.g. not well-formed)
}
The .NET API sports an XMLReader component with a similar API, and one of the first fully
compliant XML parsers, expat, utilizes the xmltok API for token-based access to an XML
data stream. Java also has StringTokenizer and StreamTokenizer for
arbitrary data streams that work along the same lines. But since imitation is the sincerest form of
flattery, let's look at xmlpull in more detail.
The xmlpull API also consists of three classes, XMLPullParser,
XMLPullParserFactory, and XMLPullException. The design of these
classes is odd to say the least.
XMLPullParserFactory creates instances of XMLPullParsers. While it
is common practice to have parser factories, I'm glad that the Java language designer decided
not to use the factory pattern everywhere, otherwise we would be dealing with StringFactory,
all over the place, and common idioms like
Reader r = new InputStreamReader(new FileInputStream(new File(new String("file.txt"))));
would have to become:
StringFactory sf = StringFactory.newInstance();
String s = sf.newString();
s.setContent("file.txt");
FileFactory ff = FileFactory.newInstance();
File f = ff.newFile();
f.setFilename(s);
FileInputStreamFactory fisf = FileInputStreamFactory.newInstance();
FileInputStream fis = fisf.newFileInputStream();
fis.setFile(f);
InputStreamReaderFactory isrf = InputStreamReaderFactory.newInstance();
InputStreamReader isr = isrf.newInputStreamReader();
isr.setFileInputStream(fis);
Argh! Some people have to put the pattern design books aside, at least for a while.
More funnies...
Produced by Michael Claßen
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URL: http://www.webreference.com/xml/column76/index.html
Created: Mar 03, 2003
Revised: Mar 03, 2003
