XMLReader

public interface XMLReader
Known Indirect Subclasses

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. See http://www.saxproject.org for further information.

Note: despite its name, this interface does not extend the standard Java Reader interface, because reading XML is a fundamentally different activity than reading character data.

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.

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.

Public Method Summary

abstract ContentHandler
getContentHandler()
Return the current content handler.
abstract DTDHandler
getDTDHandler()
Return the current DTD handler.
abstract EntityResolver
getEntityResolver()
Return the current entity resolver.
abstract ErrorHandler
getErrorHandler()
Return the current error handler.
abstract boolean
getFeature(String name)
Look up the value of a feature flag.
abstract Object
getProperty(String name)
Look up the value of a property.
abstract void
parse(InputSource input)
Parse an XML document.
abstract void
parse(String systemId)
Parse an XML document from a system identifier (URI).
abstract void
setContentHandler(ContentHandler handler)
Allow an application to register a content event handler.
abstract void
setDTDHandler(DTDHandler handler)
Allow an application to register a DTD event handler.
abstract void
setEntityResolver(EntityResolver resolver)
Allow an application to register an entity resolver.
abstract void
setErrorHandler(ErrorHandler handler)
Allow an application to register an error event handler.
abstract void
setFeature(String name, boolean value)
Set the value of a feature flag.
abstract void
setProperty(String name, Object value)
Set the value of a property.

Public Methods

public abstract ContentHandler getContentHandler ()

Return the current content handler.

Returns
  • The current content handler, or null if none has been registered.

public abstract DTDHandler getDTDHandler ()

Return the current DTD handler.

Returns
  • The current DTD handler, or null if none has been registered.

public abstract EntityResolver getEntityResolver ()

Return the current entity resolver.

Returns
  • The current entity resolver, or null if none has been registered.

public abstract ErrorHandler getErrorHandler ()

Return the current error handler.

Returns
  • The current error handler, or null if none has been registered.

public abstract boolean getFeature (String name)

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 Parser, 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.

Typical usage is something like this:

 XMLReader r = new MySAXDriver();

                         // try to activate validation
 try {
   r.setFeature("http://xml.org/sax/features/validation", true);
 } catch (SAXException e) {
   System.err.println("Cannot activate validation.");
 }

                         // register event handlers
 r.setContentHandler(new MyContentHandler());
 r.setErrorHandler(new MyErrorHandler());

                         // parse the first document
 try {
   r.parse("http://www.foo.com/mydoc.xml");
 } catch (IOException e) {
   System.err.println("I/O exception reading XML document");
 } catch (SAXException e) {
   System.err.println("XML exception reading document.");
 }
 

Implementors are free (and encouraged) to invent their own features, using names built on their own URIs.

Parameters
name The feature name, which is a fully-qualified URI.
Returns
  • The current value of the feature (true or false).
Throws
SAXNotRecognizedException If the feature value can't be assigned or retrieved.
SAXNotSupportedException When the XMLReader recognizes the feature name but cannot determine its value at this time.

public abstract Object getProperty (String name)

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.

Parameters
name The property name, which is a fully-qualified URI.
Returns
  • The current value of the property.
Throws
SAXNotRecognizedException If the property value can't be assigned or retrieved.
SAXNotSupportedException When the XMLReader recognizes the property name but cannot determine its value at this time.

public abstract void parse (InputSource input)

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.

Parameters
input The input source for the top-level of the XML document.
Throws
SAXException Any SAX exception, possibly wrapping another exception.
IOException An IO exception from the parser, possibly from a byte stream or character stream supplied by the application.