NON-Blocking XMLReader

AsyncXMLReader implements org.xml.sax.XMLReader interface.
So it can be used just like any standard SAX Parser implementation.

But It also supports non-blocking parsing, So that it can be used with NIO.

Let us see how to use it in non-blocking mode.

Rather than using org.xml.sax.InputSource, we use ChannelInputSource:

import jlibs.xml.sax.async.ChannelInputSource;

InputSource source = new ChannelInputSource(socketChannel);

Note that ChannelInputSource is used for non-blocking input.

To parse in non-blocking mode, instead of doing reader.parse(source) we will do the following:

Feeder feeder = reader.createFeeder(source);
feeder = feeder.feed();

We are using non-blocking input, thus we are not feeding entire xml document to the reader in one shot. we should keep feeding the reader, as an when data is ready to read from socketChannel. This concept is abstracted into Feeder class. When data is ready to be read from socketChannel, we call feeder.feed(). When feeding is complete, feeder.feed() returns null.

But one interesing thing to be noted is, feeder.feed() returns Feeder. The returned Feeder could be the same feeder object or different one. For example here the feeder returned might be for external dtd, in case you have resolved external dtd with another ChannelInputSource.

SocketChannel channel = (SocketChannel)feeder.byteChannel();
// enable read interest on channel

feeder.byteChannel() returns the actual ReadableByteChannel on which more input required. Now you can add read interest on this channel, and when data is ready to read, you can resume feeding by calling feeder.feed().

You can use both blocking and non-blocking inputs intermixed. for example xml document might be feeded from non-blocking input where as the dtd it is referring may be from a blocking input (local file)