1 // SAX entity resolver.
2 // http://www.saxproject.org
3 // No warranty; no copyright -- use this as you will.
4 // $Id: EntityResolver.java,v 1.10 2002/01/30 21:13:44 dbrownell Exp $
5 
6 package org.xml.sax;
7 
8 import java.io.IOException;
9 
10 
11 /**
12  * Basic interface for resolving entities.
13  *
14  * <blockquote>
15  * <em>This module, both source code and documentation, is in the
16  * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em>
17  * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a>
18  * for further information.
19  * </blockquote>
20  *
21  * <p>If a SAX application needs to implement customized handling
22  * for external entities, it must implement this interface and
23  * register an instance with the SAX driver using the
24  * {@link org.xml.sax.XMLReader#setEntityResolver setEntityResolver}
25  * method.</p>
26  *
27  * <p>The XML reader will then allow the application to intercept any
28  * external entities (including the external DTD subset and external
29  * parameter entities, if any) before including them.</p>
30  *
31  * <p>Many SAX applications will not need to implement this interface,
32  * but it will be especially useful for applications that build
33  * XML documents from databases or other specialised input sources,
34  * or for applications that use URI types other than URLs.</p>
35  *
36  * <p>The following resolver would provide the application
37  * with a special character stream for the entity with the system
38  * identifier "http://www.myhost.com/today":</p>
39  *
40  * <pre>
41  * import org.xml.sax.EntityResolver;
42  * import org.xml.sax.InputSource;
43  *
44  * public class MyResolver implements EntityResolver {
45  *   public InputSource resolveEntity (String publicId, String systemId)
46  *   {
47  *     if (systemId.equals("http://www.myhost.com/today")) {
48  *              // return a special input source
49  *       MyReader reader = new MyReader();
50  *       return new InputSource(reader);
51  *     } else {
52  *              // use the default behaviour
53  *       return null;
54  *     }
55  *   }
56  * }
57  * </pre>
58  *
59  * <p>The application can also use this interface to redirect system
60  * identifiers to local URIs or to look up replacements in a catalog
61  * (possibly by using the public identifier).</p>
62  *
63  * @since SAX 1.0
64  * @author David Megginson
65  * @version 2.0.1 (sax2r2)
66  * @see org.xml.sax.XMLReader#setEntityResolver
67  * @see org.xml.sax.InputSource
68  */
69 public interface EntityResolver {
70 
71 
72     /**
73      * Allow the application to resolve external entities.
74      *
75      * <p>The parser will call this method before opening any external
76      * entity except the top-level document entity.  Such entities include
77      * the external DTD subset and external parameter entities referenced
78      * within the DTD (in either case, only if the parser reads external
79      * parameter entities), and external general entities referenced
80      * within the document element (if the parser reads external general
81      * entities).  The application may request that the parser locate
82      * the entity itself, that it use an alternative URI, or that it
83      * use data provided by the application (as a character or byte
84      * input stream).</p>
85      *
86      * <p>Application writers can use this method to redirect external
87      * system identifiers to secure and/or local URIs, to look up
88      * public identifiers in a catalogue, or to read an entity from a
89      * database or other input source (including, for example, a dialog
90      * box).  Neither XML nor SAX specifies a preferred policy for using
91      * public or system IDs to resolve resources.  However, SAX specifies
92      * how to interpret any InputSource returned by this method, and that
93      * if none is returned, then the system ID will be dereferenced as
94      * a URL.  </p>
95      *
96      * <p>If the system identifier is a URL, the SAX parser must
97      * resolve it fully before reporting it to the application.</p>
98      *
99      * @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      */
resolveEntity(String publicId, String systemId)113     public abstract InputSource resolveEntity (String publicId,
114                            String systemId)
115     throws SAXException, IOException;
116 
117 }
118 
119 // end of EntityResolver.java
120