libjava/org/xml/sax/EntityResolver.java

   1 // SAX entity resolver.
   2 // http://www.saxproject.org
   3 // No warranty; no copyright -- use this as you will.
   4 // $Id: EntityResolver.java,v 1.7.2.3 2002/01/29 21:34:14 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      */
 113     public abstract InputSource resolveEntity (String publicId,
 114                                                String systemId)
 115         throws SAXException, IOException;
 116
 117 }
 118
 119 // end of EntityResolver.java