Interface Summary : IBaseXMLReader

Interface for reading an XML document using callbacks.
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):

  1. it adds a standard way to query and set features and properties; and
  2. it adds Namespace support, which is required for many higher-level XML standards.

There are adapters available to convert a SAX1 Parser to a SAX2 XMLReader and vice-versa.


Since : SAX 2.0
See : IXMLFilter

Methods

function getFeature(SAXString) : Boolean
procedure setFeature(SAXString, Boolean)
function getProperty(SAXString) : IProperty
procedure setErrorHandler(IErrorHandler)
function getErrorHandler() : IErrorHandler
procedure setEntityResolver(IEntityResolver)
function getEntityResolver() : IEntityResolver
procedure parse(IInputSource)
procedure parse(SAXString)

Properties



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.


Parameter : name The feature name, which is a fully-qualified URI.
Result : The current value of the feature (true or false).
Exception : ESAXNotRecognizedException If the feature value can't be assigned or retrieved.
Exception : ESAXNotSupportedException When the XMLReader recognizes the feature name but cannot determine its value at this time.
See : IXMLReader.setFeature

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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.


Parameter : name The feature name, which is a fully-qualified URI.
Parameter : state The requested value of the feature (true or false).
Exception : ESAXNotRecognizedException If the feature value can't be assigned or retrieved.
Exception : ESAXNotSupportedException When the XMLReader recognizes the feature name but cannot set the requested value.
See : IXMLReader.getFeature

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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.


Parameter : name The property name, which is a fully-qualified URI.
Result : s An Interface that allows the getting and setting of the property
Exception : ESAXNotRecognizedException If the property interface cannot be retrieved.
Exception : ESAXNotSupportedException When the XMLReader recognizes the property name but cannot determine its interface value at this time.

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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.


Parameter : handler The error handler.
See : IXMLReader.getErrorHandler

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function getErrorHandler() : IErrorHandler;

Return the current error handler.
Result : The current error handler, or nil if none has been registered.
See : IXMLReader.setErrorHandler

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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.


Parameter : resolver The entity resolver.
See : IXMLReader.getEntityResolver

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function getEntityResolver() : IEntityResolver;

Return the current entity resolver.
Result : The current entity resolver, or nil if none has been registered.
See : IXMLReader.setEntityResolver

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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.


Parameter : source The input source for the top-level of the XML document.
Exception : ESAXException Any SAX exception.
Exception : Exception An IO exception from the parser, possibly from a byte stream supplied by the application.
See : TInputSource
See : IXMLReader.parse(SAXString)
See : IXMLReader.setEntityResolver
See : IXMLReader.setDTDHandler
See : IXMLReader.setContentHandler
See : IXMLReader.setErrorHandler

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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.


Parameter : systemId The system identifier (URI).
Exception : ESAXException Any SAX exception.
Exception : Exception An IO exception from the parser, possibly from a byte stream supplied by the application.
See : IXMLReader.parse(TInputSource)

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ErrorHandler

Extension property to get and set the ErrorHandler
Result : The current Error handler, or nil if none has been registered.
See : IXMLReader.getErrorHandler
See : IXMLReader.setErrorHandler

property ErrorHandler: IErrorHandler read getErrorHandler write setErrorHandler

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EntityResolver

Extension property to get and set the EntityResolver
Result : The current content handler, or nil if none has been registered.
See : IXMLReader.getEntityResolver
See : IXMLReader.setEntityResolver

property EntityResolver: IEntityResolver read getEntityResolver write setEntityResolver

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Features

Extension property to get and set the IXMLReader's features @index name The feature name, which is a fully-qualified URI.
Exception : ESAXNotRecognizedException When the XMLReader does not recognize the feature name.
Exception : ESAXNotSupportedException When the XMLReader recognizes the feature name but cannot set the requested value.
Result : The state of the feature (true or false)
See : IXMLReader.getFeature
See : IXMLReader.setFeature

property Features[const name: SAXString]: Boolean read getFeature write setFeature

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Properties

Extension property to get the IXMLReader's property interfaces @index name The property name, which is a fully-qualified URI.
Exception : ESAXNotRecognizedException When the XMLReader does not recognize the property name.
Exception : ESAXNotSupportedException When the XMLReader recognizes the property name but cannot set the requested value.
Result : The value stored in the property as an IProperty interface
See : IXMLReader.getProperty

property Properties[const name: SAXString]: IProperty read getProperty

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