1   // SAX entity resolver.
    2   // http://www.saxproject.org
    3   // No warranty; no copyright -- use this as you will.
    4   // $Id: EntityResolver.java 226184 2005-04-08 10:53:24Z neeraj $
    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