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Package overview for net.sf.saxon.event
This package provides classes that feed SAX-like events from one tree to another.
Many of these classes are associated with serializing the output of a stylesheet, but there
are also classes for building a tree from a stream of events, for stripping whitespace, and
so on.
The Receiver interface defines a class that accepts a stream of events, with one method
defined for each kind of event. The events are modelled on the design of SAX, but adapted
to the XPath data model and to the use of Saxon's NamePool. Attributes and namespaces are
notified individually after the start of the relevant element.
The immediate output of node constructors in a query or stylesheet goes to a SequenceReceiver.
This is a subclass of Receiver that can handle an arbitrary sequence, containing atomic values
as well as nodes. When constructing the content of an element, a ComplexContentOutputter is used;
when constructing the content of a node such as a text node or attribute, a SequenceOutputter
is used instead.
The final destination of the push pipeline is sometimes a serializer, and sometimes a tree builder.
The final serialization classes are subclasses of Emitter, but some of the serialization work
(such as indentation or application of character maps) is done by other classes on the pipeline. These
are generally constructed by extending the ProxyReceiver class.
The Emitter is an abstract implementation of the Receiver interface. As well as supporting
the Receiver interface, it provides methods for controlling the destination of serialized output
(a Writer or OutputStream) and for setting serialization properties (in a Properties object).
In practice nearly all the implementations of Receiver are currently subclasses of Emitter,
but this may change in the future.
The package includes emitters for the standard output methods xml, html, and text, and
proxy emitters to allow a sequence of filters to be applied to the output.
,
The class ContentHandlerProxy allows events to be converted into standard SAX events and
sent to a SAX2 ContentHandler. Similarly, the class ProxyReceiver acts as a
ContentHandler, accepting SAX2 events and feeding them into a Receiver pipeline.
The class Builder is a Receiver that constructs a tree representation of the
document in memory. There are two subclasses for Saxon's two native tree models. Other classes such as
a Stripper and a NamespaceReducer are used to modify the document by adding
filters to the pipeline.
Saxon's schema validator is also implemented using this push pipeline model. The classes that perform
schema validation, however, are part of a different package: com.saxonica.validate.
Michael H. Kay
Saxonica Limited
9 February 2005