1 /*
   2  * Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package org.xml.sax;
  27 
  28 import java.io.IOException;
  29 
  30 
  31 /**
  32  * Basic interface for resolving entities.
  33  *
  34  * <p>If a SAX application needs to implement customized handling
  35  * for external entities, it must implement this interface and
  36  * register an instance with the SAX driver using the
  37  * {@link org.xml.sax.XMLReader#setEntityResolver setEntityResolver}
  38  * method.</p>
  39  *
  40  * <p>The XML reader will then allow the application to intercept any
  41  * external entities (including the external DTD subset and external
  42  * parameter entities, if any) before including them.</p>
  43  *
  44  * <p>Many SAX applications will not need to implement this interface,
  45  * but it will be especially useful for applications that build
  46  * XML documents from databases or other specialised input sources,
  47  * or for applications that use URI types other than URLs.</p>
  48  *
  49  * <p>The following resolver would provide the application
  50  * with a special character stream for the entity with the system
  51  * identifier "http://www.myhost.com/today":</p>
  52  *
  53  * <pre>
  54  * import org.xml.sax.EntityResolver;
  55  * import org.xml.sax.InputSource;
  56  *
  57  * public class MyResolver implements EntityResolver {
  58  *   public InputSource resolveEntity (String publicId, String systemId)
  59  *   {
  60  *     if (systemId.equals("http://www.myhost.com/today")) {
  61  *              // return a special input source
  62  *       MyReader reader = new MyReader();
  63  *       return new InputSource(reader);
  64  *     } else {
  65  *              // use the default behaviour
  66  *       return null;
  67  *     }
  68  *   }
  69  * }
  70  * </pre>
  71  *
  72  * <p>The application can also use this interface to redirect system
  73  * identifiers to local URIs or to look up replacements in a catalog
  74  * (possibly by using the public identifier).</p>
  75  *
  76  * @since 1.4, SAX 1.0
  77  * @author David Megginson
  78  * @see org.xml.sax.XMLReader#setEntityResolver
  79  * @see org.xml.sax.InputSource
  80  */
  81 public interface EntityResolver {
  82 
  83 
  84     /**
  85      * Allow the application to resolve external entities.
  86      *
  87      * <p>The parser will call this method before opening any external
  88      * entity except the top-level document entity.  Such entities include
  89      * the external DTD subset and external parameter entities referenced
  90      * within the DTD (in either case, only if the parser reads external
  91      * parameter entities), and external general entities referenced
  92      * within the document element (if the parser reads external general
  93      * entities).  The application may request that the parser locate
  94      * the entity itself, that it use an alternative URI, or that it
  95      * use data provided by the application (as a character or byte
  96      * input stream).</p>
  97      *
  98      * <p>Application writers can use this method to redirect external
  99      * system identifiers to secure and/or local URIs, to look up
 100      * public identifiers in a catalogue, or to read an entity from a
 101      * database or other input source (including, for example, a dialog
 102      * box).  Neither XML nor SAX specifies a preferred policy for using
 103      * public or system IDs to resolve resources.  However, SAX specifies
 104      * how to interpret any InputSource returned by this method, and that
 105      * if none is returned, then the system ID will be dereferenced as
 106      * a URL.  </p>
 107      *
 108      * <p>If the system identifier is a URL, the SAX parser must
 109      * resolve it fully before reporting it to the application.</p>
 110      *
 111      * @param publicId The public identifier of the external entity
 112      *        being referenced, or null if none was supplied.
 113      * @param systemId The system identifier of the external entity
 114      *        being referenced.
 115      * @return An InputSource object describing the new input source,
 116      *         or null to request that the parser open a regular
 117      *         URI connection to the system identifier.
 118      * @exception org.xml.sax.SAXException Any SAX exception, possibly
 119      *            wrapping another exception.
 120      * @exception java.io.IOException A Java-specific IO exception,
 121      *            possibly the result of creating a new InputStream
 122      *            or Reader for the InputSource.
 123      * @see org.xml.sax.InputSource
 124      */
 125     public abstract InputSource resolveEntity (String publicId,
 126                                                String systemId)
 127         throws SAXException, IOException;
 128 
 129 }
 130 
 131 // end of EntityResolver.java