Module java.xml
Package org.xml.sax

# Interface XMLReader

All Known Subinterfaces:
  `XMLFilter`

All Known Implementing Classes:
  `ParserAdapter`, `XMLFilterImpl`

public interface XMLReader
Interface for reading an XML document using callbacks.

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.

API 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.
Since:
  1.4, SAX 2.0
See Also:
  - `XMLFilter`
  - `ParserAdapter`
  - `XMLReaderAdapter`

- ## Method Summary

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

- ## Method Details

  - ### getFeature

    boolean getFeature(String name) throws SAXNotRecognizedException, SAXNotSupportedException
    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.
    See Also:
      - `setFeature(java.lang.String, boolean)`

  - ### setFeature

    void setFeature(String name, boolean value) throws SAXNotRecognizedException, SAXNotSupportedException
    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.

    Parameters:
      `name` - The feature name, which is a fully-qualified URI.
      `value` - The requested 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 set the requested value.
    See Also:
      - `getFeature(java.lang.String)`

  - ### getProperty

    Object getProperty(String name) throws SAXNotRecognizedException, SAXNotSupportedException
    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.
    See Also:
      - `setProperty(java.lang.String, java.lang.Object)`

  - ### setProperty

    void setProperty(String name, Object value) throws SAXNotRecognizedException, SAXNotSupportedException
    Set 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 to be unable to change the current value. Some property values may be immutable or mutable only in specific contexts, such as before, during, or after a parse.

    XMLReaders are not required to recognize setting any specific property names, though a core set is defined by SAX2.

    This method is also the standard mechanism for setting extended handlers.

    Parameters:
      `name` - The property name, which is a fully-qualified URI.
      `value` - The requested value for the property.
    Throws:
      `SAXNotRecognizedException` - If the property value can't be assigned or retrieved.
      `SAXNotSupportedException` - When the XMLReader recognizes the property name but cannot set the requested value.

  - ### setEntityResolver

    void setEntityResolver(EntityResolver resolver)
    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.

    Parameters:
      `resolver` - The entity resolver.
    See Also:
      - `getEntityResolver()`

  - ### getEntityResolver

    EntityResolver getEntityResolver()
    Return the current entity resolver.
    Returns:
      The current entity resolver, or null if none has been registered.
    See Also:
      - `setEntityResolver(org.xml.sax.EntityResolver)`

  - ### setDTDHandler

    void setDTDHandler(DTDHandler handler)
    Allow an application to register a DTD event handler.

    If the application does not register a DTD handler, all DTD events reported by the SAX parser will be silently ignored.

    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.

    Parameters:
      `handler` - The DTD handler.
    See Also:
      - `getDTDHandler()`

  - ### getDTDHandler

    DTDHandler getDTDHandler()
    Return the current DTD handler.
    Returns:
      The current DTD handler, or null if none has been registered.
    See Also:
      - `setDTDHandler(org.xml.sax.DTDHandler)`

  - ### setContentHandler

    void setContentHandler(ContentHandler handler)
    Allow an application to register a content event handler.

    If the application does not register a content handler, all content events reported by the SAX parser will be silently ignored.

    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.

    Parameters:
      `handler` - The content handler.
    See Also:
      - `getContentHandler()`

  - ### getContentHandler

    ContentHandler getContentHandler()
    Return the current content handler.
    Returns:
      The current content handler, or null if none has been registered.
    See Also:
      - `setContentHandler(org.xml.sax.ContentHandler)`

  - ### setErrorHandler

    void setErrorHandler(ErrorHandler handler)
    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.

    Parameters:
      `handler` - The error handler.
    See Also:
      - `getErrorHandler()`

  - ### getErrorHandler

    ErrorHandler getErrorHandler()
    Return the current error handler.
    Returns:
      The current error handler, or null if none has been registered.
    See Also:
      - `setErrorHandler(org.xml.sax.ErrorHandler)`

  - ### parse

    void parse(InputSource input) throws IOException, SAXException
    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.
    See Also:
      - `InputSource`
      - `parse(java.lang.String)`
      - `setEntityResolver(org.xml.sax.EntityResolver)`
      - `setDTDHandler(org.xml.sax.DTDHandler)`
      - `setContentHandler(org.xml.sax.ContentHandler)`
      - `setErrorHandler(org.xml.sax.ErrorHandler)`

  - ### parse

    void parse(String systemId) throws IOException, SAXException
    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:

         parse(new InputSource(systemId));

    If the system identifier is a URL, it must be fully resolved by the application before it is passed to the parser.

    Parameters:
      `systemId` - The system identifier (URI).
    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.
    See Also:
      - `parse(org.xml.sax.InputSource)`