This module, both source code and documentation, is in the Public Domain, and comes with NO WARRANTY.
XMLReader is the interface that an XML parser's SAX2 driver must implement. This interface allows an application to set and query features and properties in the parser, to register event handlers for document processing, and to initiate a document parse.
The XMLReader interface is split into a common base interface, IBaseXMLReader, and the actual IXMLReader specification which derives from it. This is done to improve type safety for applications which can handle both, standard and buffered XMLReader implementations (see BSAX.pas). Most applications need not be aware of this split definition.
All SAX interfaces are assumed to be synchronous: the parse methods must not return until parsing is complete, and readers must wait for an event-handler callback to return before reporting the next event.
This interface replaces the (now deprecated) SAX 1.0 Parser interface. The XMLReader interface contains two important enhancements over the old Parser interface (as well as some minor ones):
There are adapters available to convert a SAX1 Parser to a SAX2 XMLReader and vice-versa.
function getFeature(const name : SAXString) : Boolean;
Look up the value of a feature flag.The feature name is any fully-qualified URI. It is possible for an XMLReader to recognize a feature name but temporarily be unable to return its value. Some feature values may be available only in specific contexts, such as before, during, or after a parse. Also, some feature values may not be programmatically accessible. (In the case of an adapter for SAX1 IParser, there is no implementation-independent way to expose whether the underlying parser is performing validation, expanding external entities, and so forth.)
All XMLReaders are required to recognize the http://xml.org/sax/features/namespaces and the http://xml.org/sax/features/namespace-prefixes feature names.
Some feature values may be available only in specific contexts, such as before, during, or after a parse.
Typical usage is something like this:
var r : IXMLReader; begin r:= TMySAXDriver.Create() as IXMLReader; // try to activate validation try r.setFeature('http://xml.org/sax/features/validation', true); except on e : ESAXException do begin Showmessage('Cannot activate validation.'); end; end; // register event handlers r.setContentHandler(TMyContentHandler.Create() as IContentHandler); r.setErrorHandler(TMyErrorHandler.Create() as IErrorHandler); // parse the first document try r.parse('file://c:/mydoc.xml'); except on e : ESAXException do begin Showmessage('XML exception reading document.'); end; on e : Exception do begin Showmessage('Exception reading document.'); end; end;
Implementors are free (and encouraged) to invent their own features, using names built on their own URIs.
procedure setFeature(const name : SAXString; value : Boolean);
Set the value of a feature flag.The feature name is any fully-qualified URI. It is possible for an XMLReader to expose a feature value but to be unable to change the current value. Some feature values may be immutable or mutable only in specific contexts, such as before, during, or after a parse.
All XMLReaders are required to support setting http://xml.org/sax/features/namespaces to true and http://xml.org/sax/features/namespace-prefixes to false.
function getProperty(const name : SAXString) : IProperty;
Look up the value of a property.The property name is any fully-qualified URI. It is possible for an XMLReader to recognize a property name but temporarily be unable to return its value Some property values may be available only in specific contexts, such as before, during, or after a parse.
XMLReaders are not required to recognize any specific property names, though an initial core set is documented for SAX2.
Implementors are free (and encouraged) to invent their own properties, using names built on their own URIs.
Within SAX for Pascal property setting is handled through the interface that is returned by the call to getProperty. This eliminates the need for multiple lookups in tight loop situations as a user can maintain a reference to the interface.
procedure setErrorHandler(const handler : IErrorHandler);
Allow an application to register an error event handler.If the application does not register an error handler, all error events reported by the SAX parser will be silently ignored; however, normal processing may not continue. It is highly recommended that all SAX applications implement an error handler to avoid unexpected bugs.
Applications may register a new or different handler in the middle of a parse, and the SAX parser must begin using the new handler immediately.
function getErrorHandler() : IErrorHandler;
Return the current error handler.procedure setEntityResolver(const resolver : IEntityResolver);
Allow an application to register an entity resolver.If the application does not register an entity resolver, the XMLReader will perform its own default resolution.
Applications may register a new or different resolver in the middle of a parse, and the SAX parser must begin using the new resolver immediately.
function getEntityResolver() : IEntityResolver;
Return the current entity resolver.procedure parse(const input : IInputSource);
Parse an XML document.The application can use this method to instruct the XML reader to begin parsing an XML document from any valid input source (a character stream, a byte stream, or a URI).
Applications may not invoke this method while a parse is in progress (they should create a new XMLReader instead for each nested XML document). Once a parse is complete, an application may reuse the same XMLReader object, possibly with a different input source. Configuration of the XMLReader object (such as handler bindings and values established for feature flags and properties) is unchanged by completion of a parse, unless the definition of that aspect of the configuration explicitly specifies other behavior. (For example, feature flags or properties exposing characteristics of the document being parsed.)
During the parse, the XMLReader will provide information about the XML document through the registered event handlers.
This method is synchronous: it will not return until parsing has ended. If a client application wants to terminate parsing early, it should throw an exception.
procedure parse(const systemId : SAXString);
Parse an XML document from a system identifier (URI).This method is a shortcut for the common case of reading a document from a system identifier. It is the exact equivalent of the following:
input:= TInputSource.Create(systemId) as IInputSource; try parse(input); finally input:= nil; end;
If the system identifier is a URL, it must be fully resolved by the application before it is passed to the parser.
ErrorHandler
Extension property to get and set the ErrorHandler
property ErrorHandler: IErrorHandler
read getErrorHandler write setErrorHandler
EntityResolver
Extension property to get and set the EntityResolver
property EntityResolver: IEntityResolver
read getEntityResolver write setEntityResolver
Features
Extension property to get and set the IXMLReader's features @index name The feature name, which is a fully-qualified URI.
property Features[const name: SAXString]: Boolean
read getFeature write setFeature
Properties
Extension property to get the IXMLReader's property interfaces @index name The property name, which is a fully-qualified URI.
property Properties[const name: SAXString]: IProperty
read getProperty