Source for org.xml.sax.EntityResolver

   1: // SAX entity resolver.
   2: // http://www.saxproject.org
   3: // No warranty; no copyright -- use this as you will.
   4: // $Id: EntityResolver.java,v 1.1 2004/12/23 22:38:42 mark 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