// SAX entity resolver.
// No warranty; no copyright -- use this as you will.
// $Id: EntityResolver.java,v 1.2 2004/09/13 21:00:18 damon Exp $
package ewesoft.xml.sax;
import ewe.io.IOException;
/**
* Basic interface for resolving entities.
*
* <p>If a SAX application needs to implement customized handling
* for external entities, it must implement this interface and
* register an instance with the SAX parser using the parser's
* setEntityResolver method.</p>
*
* <p>The parser will then allow the application to intercept any
* external entities (including the external DTD subset and external
* parameter entities, if any) before including them.</p>
*
* <p>Many SAX applications will not need to implement this interface,
* but it will be especially useful for applications that build
* XML documents from databases or other specialised input sources,
* or for applications that use URI types other than URLs.</p>
*
* <p>The following resolver would provide the application
* with a special character stream for the entity with the system
* identifier "http://www.myhost.com/today":</p>
*
* <pre>
* import ewesoft.xml.sax.EntityResolver;
* import ewesoft.xml.sax.InputSource;
*
* public class MyResolver implements EntityResolver {
* public InputSource resolveEntity (String publicId, String systemId)
* {
* if (systemId.equals("http://www.myhost.com/today")) {
* // return a special input source
* MyReader reader = new MyReader();
* return new InputSource(reader);
* } else {
* // use the default behaviour
* return null;
* }
* }
* }
* </pre>
*
* <p>The application can also use this interface to redirect system
* identifiers to local URIs or to look up replacements in a catalog
* (possibly by using the public identifier).</p>
*
* <p>The HandlerBase class implements the default behaviour for
* this interface, which is simply always to return null (to request
* that the parser use the default system identifier).</p>
*
* @author David Megginson (ak117@freenet.carleton.ca)
* @version 1.0
* @see ewesoft.xml.sax.Parser#setEntityResolver
* @see ewesoft.xml.sax.InputSource
* @see ewesoft.xml.sax.HandlerBase
*/
public interface EntityResolver {
/**
* Allow the application to resolve external entities.
*
* <p>The Parser will call this method before opening any external
* entity except the top-level document entity (including the
* external DTD subset, external entities referenced within the
* DTD, and external entities referenced within the document
* element): the application may request that the parser resolve
* the entity itself, that it use an alternative URI, or that it
* use an entirely different input source.</p>
*
* <p>Application writers can use this method to redirect external
* system identifiers to secure and/or local URIs, to look up
* public identifiers in a catalogue, or to read an entity from a
* database or other input source (including, for example, a dialog
* box).</p>
*
* <p>If the system identifier is a URL, the SAX parser must
* resolve it fully before reporting it to the application.</p>
*
* @param publicId The public identifier of the external entity
* being referenced, or null if none was supplied.
* @param systemId The system identifier of the external entity
* being referenced.
* @return An InputSource object describing the new input source,
* or null to request that the parser open a regular
* URI connection to the system identifier.
* @exception ewesoft.xml.sax.SAXException Any SAX exception, possibly
* wrapping another exception.
* @exception java.io.IOException A Java-specific IO exception,
* possibly the result of creating a new InputStream
* or Reader for the InputSource.
* @see ewesoft.xml.sax.InputSource
*/
public abstract InputSource resolveEntity (String publicId,
String systemId)
throws SAXException, IOException;
}