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// SAX entity resolver.
// http://www.saxproject.org
// No warranty; no copyright -- use this as you will.
// $Id: EntityResolver.java,v 1.7.2.3 2002/01/29 21:34:14 dbrownell Exp $
package org.xml.sax;
import java.io.IOException;
/**
* Basic interface for resolving entities.
*
* <blockquote>
* <em>This module, both source code and documentation, is in the
* Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
* See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
* for further information.
* </blockquote>
*
* <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 driver using the
* {@link org.xml.sax.XMLReader#setEntityResolver setEntityResolver}
* method.</p>
*
* <p>The XML reader 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 org.xml.sax.EntityResolver;
* import org.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>
*
* @since SAX 1.0
* @author David Megginson
* @version 2.0.1 (sax2r2)
* @see org.xml.sax.XMLReader#setEntityResolver
* @see org.xml.sax.InputSource
*/
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. Such entities include
* the external DTD subset and external parameter entities referenced
* within the DTD (in either case, only if the parser reads external
* parameter entities), and external general entities referenced
* within the document element (if the parser reads external general
* entities). The application may request that the parser locate
* the entity itself, that it use an alternative URI, or that it
* use data provided by the application (as a character or byte
* input stream).</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). Neither XML nor SAX specifies a preferred policy for using
* public or system IDs to resolve resources. However, SAX specifies
* how to interpret any InputSource returned by this method, and that
* if none is returned, then the system ID will be dereferenced as
* a URL. </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 org.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 org.xml.sax.InputSource
*/
public abstract InputSource resolveEntity (String publicId,
String systemId)
throws SAXException, IOException;
}
// end of EntityResolver.java
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