001    // SAX entity resolver.
002    // http://www.saxproject.org
003    // No warranty; no copyright -- use this as you will.
004    // $Id: EntityResolver.java,v 1.1 2004/12/23 22:38:42 mark Exp $
005    
006    package org.xml.sax;
007    
008    import java.io.IOException;
009    
010    
011    /**
012     * Basic interface for resolving entities.
013     *
014     * <blockquote>
015     * <em>This module, both source code and documentation, is in the
016     * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
017     * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
018     * for further information.
019     * </blockquote>
020     *
021     * <p>If a SAX application needs to implement customized handling
022     * for external entities, it must implement this interface and
023     * register an instance with the SAX driver using the
024     * {@link org.xml.sax.XMLReader#setEntityResolver setEntityResolver}
025     * method.</p>
026     *
027     * <p>The XML reader will then allow the application to intercept any
028     * external entities (including the external DTD subset and external
029     * parameter entities, if any) before including them.</p>
030     *
031     * <p>Many SAX applications will not need to implement this interface,
032     * but it will be especially useful for applications that build
033     * XML documents from databases or other specialised input sources,
034     * or for applications that use URI types other than URLs.</p>
035     *
036     * <p>The following resolver would provide the application
037     * with a special character stream for the entity with the system
038     * identifier "http://www.myhost.com/today":</p>
039     *
040     * <pre>
041     * import org.xml.sax.EntityResolver;
042     * import org.xml.sax.InputSource;
043     *
044     * public class MyResolver implements EntityResolver {
045     *   public InputSource resolveEntity (String publicId, String systemId)
046     *   {
047     *     if (systemId.equals("http://www.myhost.com/today")) {
048     *              // return a special input source
049     *       MyReader reader = new MyReader();
050     *       return new InputSource(reader);
051     *     } else {
052     *              // use the default behaviour
053     *       return null;
054     *     }
055     *   }
056     * }
057     * </pre>
058     *
059     * <p>The application can also use this interface to redirect system
060     * identifiers to local URIs or to look up replacements in a catalog
061     * (possibly by using the public identifier).</p>
062     *
063     * @since SAX 1.0
064     * @author David Megginson
065     * @version 2.0.1 (sax2r2)
066     * @see org.xml.sax.XMLReader#setEntityResolver
067     * @see org.xml.sax.InputSource
068     */
069    public interface EntityResolver {
070    
071    
072        /**
073         * Allow the application to resolve external entities.
074         *
075         * <p>The parser will call this method before opening any external
076         * entity except the top-level document entity.  Such entities include
077         * the external DTD subset and external parameter entities referenced
078         * within the DTD (in either case, only if the parser reads external
079         * parameter entities), and external general entities referenced
080         * within the document element (if the parser reads external general
081         * entities).  The application may request that the parser locate
082         * the entity itself, that it use an alternative URI, or that it
083         * use data provided by the application (as a character or byte
084         * input stream).</p>
085         *
086         * <p>Application writers can use this method to redirect external
087         * system identifiers to secure and/or local URIs, to look up
088         * public identifiers in a catalogue, or to read an entity from a
089         * database or other input source (including, for example, a dialog
090         * box).  Neither XML nor SAX specifies a preferred policy for using
091         * public or system IDs to resolve resources.  However, SAX specifies
092         * how to interpret any InputSource returned by this method, and that
093         * if none is returned, then the system ID will be dereferenced as
094         * a URL.  </p>
095         *
096         * <p>If the system identifier is a URL, the SAX parser must
097         * resolve it fully before reporting it to the application.</p>
098         *
099         * @param publicId The public identifier of the external entity
100         *        being referenced, or null if none was supplied.
101         * @param systemId The system identifier of the external entity
102         *        being referenced.
103         * @return An InputSource object describing the new input source,
104         *         or null to request that the parser open a regular
105         *         URI connection to the system identifier.
106         * @exception org.xml.sax.SAXException Any SAX exception, possibly
107         *            wrapping another exception.
108         * @exception java.io.IOException A Java-specific IO exception,
109         *            possibly the result of creating a new InputStream
110         *            or Reader for the InputSource.
111         * @see org.xml.sax.InputSource
112         */
113        public abstract InputSource resolveEntity (String publicId,
114                                                   String systemId)
115            throws SAXException, IOException;
116    
117    }
118    
119    // end of EntityResolver.java