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