1// EntityResolver2.java - Extended SAX entity resolver. 2// http://www.saxproject.org 3// No warranty; no copyright -- use this as you will. 4// $Id: EntityResolver2.java,v 1.2 2002/01/12 19:20:08 dbrownell Exp $ 5 6package org.xml.sax.ext; 7 8import java.io.IOException; 9 10import org.xml.sax.EntityResolver; 11import org.xml.sax.InputSource; 12import org.xml.sax.XMLReader; 13import org.xml.sax.SAXException; 14 15 16/** 17 * Extended interface for mapping external entity references to input 18 * sources, or providing a missing external subset. The 19 * {@link XMLReader#setEntityResolver XMLReader.setEntityResolver()} method 20 * is used to provide implementations of this interface to parsers. 21 * When a parser uses the methods in this interface, the 22 * {@link EntityResolver2#resolveEntity EntityResolver2.resolveEntity()} 23 * method (in this interface) is used <em>instead of</em> the older (SAX 1.0) 24 * {@link EntityResolver#resolveEntity EntityResolver.resolveEntity()} method. 25 * 26 * <blockquote> 27 * <em>This module, both source code and documentation, is in the 28 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em> 29 * </blockquote> 30 * 31 * <p>If a SAX application requires the customized handling which this 32 * interface defines for external entities, it must ensure that it uses 33 * an XMLReader with the 34 * <em>http://xml.org/sax/features/use-entity-resolver2</em> feature flag 35 * set to <em>true</em> (which is its default value when the feature is 36 * recognized). If that flag is unrecognized, or its value is false, 37 * or the resolver does not implement this interface, then only the 38 * {@link EntityResolver} method will be used. 39 * </p> 40 * 41 * <p>That supports three categories of application that modify entity 42 * resolution. <em>Old Style</em> applications won't know about this interface; 43 * they will provide an EntityResolver. 44 * <em>Transitional Mode</em> provide an EntityResolver2 and automatically 45 * get the benefit of its methods in any systems (parsers or other tools) 46 * supporting it, due to polymorphism. 47 * Both <em>Old Style</em> and <em>Transitional Mode</em> applications will 48 * work with any SAX2 parser. 49 * <em>New style</em> applications will fail to run except on SAX2 parsers 50 * that support this particular feature. 51 * They will insist that feature flag have a value of "true", and the 52 * EntityResolver2 implementation they provide might throw an exception 53 * if the original SAX 1.0 style entity resolution method is invoked. 54 * </p> 55 * 56 * @see org.xml.sax.XMLReader#setEntityResolver 57 * 58 * @since SAX 2.0 (extensions 1.1 alpha) 59 * @author David Brownell 60 * @version TBD 61 */ 62public interface EntityResolver2 extends EntityResolver 63{ 64 /** 65 * Allows applications to provide an external subset for documents 66 * that don't explicitly define one. Documents with DOCTYPE declarations 67 * that omit an external subset can thus augment the declarations 68 * available for validation, entity processing, and attribute processing 69 * (normalization, defaulting, and reporting types including ID). 70 * This augmentation is reported 71 * through the {@link LexicalHandler#startDTD startDTD()} method as if 72 * the document text had originally included the external subset; 73 * this callback is made before any internal subset data or errors 74 * are reported.</p> 75 * 76 * <p>This method can also be used with documents that have no DOCTYPE 77 * declaration. When the root element is encountered, 78 * but no DOCTYPE declaration has been seen, this method is 79 * invoked. If it returns a value for the external subset, that root 80 * element is declared to be the root element, giving the effect of 81 * splicing a DOCTYPE declaration at the end the prolog of a document 82 * that could not otherwise be valid. The sequence of parser callbacks 83 * in that case logically resembles this:</p> 84 * 85 * <pre> 86 * ... comments and PIs from the prolog (as usual) 87 * startDTD ("rootName", source.getPublicId (), source.getSystemId ()); 88 * startEntity ("[dtd]"); 89 * ... declarations, comments, and PIs from the external subset 90 * endEntity ("[dtd]"); 91 * endDTD (); 92 * ... then the rest of the document (as usual) 93 * startElement (..., "rootName", ...); 94 * </pre> 95 * 96 * <p>Note that the InputSource gets no further resolution. 97 * Implementations of this method may wish to invoke 98 * {@link #resolveEntity resolveEntity()} to gain benefits such as use 99 * of local caches of DTD entities. Also, this method will never be 100 * used by a (non-validating) processor that is not including external 101 * parameter entities. </p> 102 * 103 * <p>Uses for this method include facilitating data validation when 104 * interoperating with XML processors that would always require 105 * undesirable network accesses for external entities, or which for 106 * other reasons adopt a "no DTDs" policy. 107 * Non-validation motives include forcing documents to include DTDs so 108 * that attributes are handled consistently. 109 * For example, an XPath processor needs to know which attibutes have 110 * type "ID" before it can process a widely used type of reference.</p> 111 * 112 * <p><strong>Warning:</strong> Returning an external subset modifies 113 * the input document. By providing definitions for general entities, 114 * it can make a malformed document appear to be well formed. 115 * </p> 116 * 117 * @param name Identifies the document root element. This name comes 118 * from a DOCTYPE declaration (where available) or from the actual 119 * root element. 120 * @param baseURI The document's base URI, serving as an additional 121 * hint for selecting the external subset. This is always an absolute 122 * URI, unless it is null because the XMLReader was given an InputSource 123 * without one. 124 * 125 * @return An InputSource object describing the new external subset 126 * to be used by the parser, or null to indicate that no external 127 * subset is provided. 128 * 129 * @exception SAXException Any SAX exception, possibly wrapping 130 * another exception. 131 * @exception IOException Probably indicating a failure to create 132 * a new InputStream or Reader, or an illegal URL. 133 */ 134 public InputSource getExternalSubset (String name, String baseURI) 135 throws SAXException, IOException; 136 137 /** 138 * Allows applications to map references to external entities into input 139 * sources, or tell the parser it should use conventional URI resolution. 140 * This method is only called for external entities which have been 141 * properly declared. 142 * This method provides more flexibility than the {@link EntityResolver} 143 * interface, supporting implementations of more complex catalogue 144 * schemes such as the one defined by the <a href= 145 "http://www.oasis-open.org/committees/entity/spec-2001-08-06.html" 146 >OASIS XML Catalogs</a> specification.</p> 147 * 148 * <p>Parsers configured to use this resolver method will call it 149 * to determine the input source to use for any external entity 150 * being included because of a reference in the XML text. 151 * That excludes the document entity, and any external entity returned 152 * by {@link #getExternalSubset getExternalSubset()}. 153 * When a (non-validating) processor is configured not to include 154 * a class of entities (parameter or general) through use of feature 155 * flags, this method is not invoked for such entities. </p> 156 * 157 * <p>Note that the entity naming scheme used here is the same one 158 * used in the {@link LexicalHandler}, or in the {@link 159 org.xml.sax.ContentHandler#skippedEntity 160 ContentHandler.skippedEntity()} 161 * method. </p> 162 * 163 * @param name Identifies the external entity being resolved. 164 * Either "[dtd]" for the external subset, or a name starting 165 * with "%" to indicate a parameter entity, or else the name of 166 * a general entity. This is never null when invoked by a SAX2 167 * parser. 168 * @param publicId The public identifier of the external entity being 169 * referenced (normalized as required by the XML specification), or 170 * null if none was supplied. 171 * @param baseURI The URI with respect to which relative systemIDs 172 * are interpreted. This is always an absolute URI, unless it is 173 * null (likely because the XMLReader was given an InputSource without 174 * one). This URI is defined by the XML specification to be the one 175 * associated with the "<" starting the relevant declaration. 176 * @param systemId The system identifier of the external entity 177 * being referenced; either a relative or absolute URI. 178 * This is never null when invoked by a SAX2 parser; only declared 179 * entities, and any external subset, are resolved by such parsers. 180 * 181 * @return An InputSource object describing the new input source to 182 * be used by the parser. Returning null directs the parser to 183 * resolve the system ID against the base URI and open a connection 184 * to resulting URI. 185 * 186 * @exception SAXException Any SAX exception, possibly wrapping 187 * another exception. 188 * @exception IOException Probably indicating a failure to create 189 * a new InputStream or Reader, or an illegal URL. 190 */ 191 public InputSource resolveEntity ( 192 String name, 193 String publicId, 194 String baseURI, 195 String systemId 196 ) throws SAXException, IOException; 197} 198