JingResolver


1   /*
2    * Copyright 1999-2005 The Apache Software Foundation.
3    *
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  package org.apache.cocoon.components.validation.jing;
17  
18  import java.io.IOException  ;
19  import java.util.Stack  ;
20  
21  import org.apache.cocoon.components.validation.impl.ValidationResolver;
22  import org.apache.excalibur.source.SourceResolver;
23  import org.xml.sax.EntityResolver  ;
24  import org.xml.sax.InputSource  ;
25  import org.xml.sax.SAXException  ;
26  import org.xml.sax.XMLReader  ;
27  
28  import com.thaiopensource.xml.sax.XMLReaderCreator;
29  
30  /**
31   * <p>A simple resolver used when parsing RELAX NG schemas through the use of
32   * <a HREF="http://www.thaiopensource.com/relaxng/jing.html">JING</a>.</p>
33   *
34   * <p>This is not thread safe and not recyclable. Once used, it <b>must</b> be
35   * garbage collected.</p>
36   *
37   * @author <a HREF="mailto:pier@betaversion.org">Pier Fumagalli</a>
38   */
39  public class JingResolver extends ValidationResolver implements XMLReaderCreator {
40  
41      /** <p>The current {@link Stack} of {@link InputSource}s being parsed. </p> */
42      private final Stack   parsedSourceStack = new Stack  ();
43  
44      /**
45       * <p>Create a new {@link JingResolver} instance.</p>
46       */
47      public JingResolver(SourceResolver sourceResolver,
48                         EntityResolver   entityResolver) {
49          super(sourceResolver, entityResolver);
50          this.parsedSourceStack.push(null);
51      }
52  
53      /**
54       * <p>Push a new {@link InputSource} in the stack used for relative URIs
55       * resolution.</p>
56       */
57      public void pushInputSource(InputSource   inputSource) {
58          this.parsedSourceStack.push(inputSource);
59      }
60  
61      /**
62       * <p>Pop the last {@link InputSource} from the stack used for relative URIs
63       * resolution.</p>
64       */
65      public InputSource   popInputSource() {
66          if (this.parsedSourceStack.empty()) return null;
67          return (InputSource  ) this.parsedSourceStack.pop();
68      }
69  
70      /**
71       * <p>Return the {@link PropertyMap} associated with this instance and usable
72       * by <a HREF="http://www.thaiopensource.com/relaxng/jing.html">JING</a>.</p>
73       */
74      //public PropertyMap getProperties() {
75      //    return this.validatorProperties;
76      //}
77  
78      /* =========================================================================== */
79      /* SAX2 ENTITY RESOLVER INTERFACE IMPLEMENTATION                               */
80      /* =========================================================================== */
81  
82      /**
83       * <p>Resolve an {@link InputSource} from a public ID and/or a system ID.</p>
84       * 
85       * <p>This method can be called only while a schema is being parsed and will
86       * resolve URIs against a dynamic {@link Stack} of {@link InputSource}s.</p>
87       *
88       * <p>Since <a HREF="http://www.thaiopensource.com/relaxng/jing.html">JING</a>
89       * doesn't offer a complete URI resolution contract, a {@link Stack} is kept
90       * for all the sources parsed while reading a schema. Keeping in mind that the
91       * last {@link InputSource} pushed in the {@link Stack} can be considered to be
92       * the "base URI" for the current resolution, full relative resolution of system
93       * IDs can be achieved this way.<p>
94       * 
95       * <p>Note that this method of resolving URIs by keeping a {@link Stack} of
96       * processed URIs is a <i>sort of a hack</i>, but it mimics the internal state
97       * of <a HREF="http://www.thaiopensource.com/relaxng/jing.html">JING</a> itself:
98       * if URI resolution fails, the {@link Stack} analysis is the first part to
99       * look at.</p>
100      * 
101      * <p>Resolution will use the {@link EntityResolver} specified at construction
102      * to resolve public IDs, and then the {@link SourceResolver} again specified at
103      * construction to resolve the system IDs and to access the underlying byte
104      * streams of the entities to be parsed.</p>
105      * 
106      * @param publicId the public ID of the entity to resolve.
107      * @param systemId the system ID of the entity to resolve.
108      * @return a <b>non-null</b> {@link InputSource} instance.
109      * @throws IOException if an I/O error occurred resolving the entity.
110      * @throws SAXException if an XML error occurred resolving the entity.
111      */
112     public InputSource   resolveEntity(String   publicId, String   systemId)
113     throws SAXException  , IOException   {
114         InputSource   source = (InputSource  ) this.parsedSourceStack.peek();
115         if (source == null) {
116             return super.resolveEntity(publicId, systemId);
117         } else {
118             return super.resolveEntity(source.getSystemId(), publicId, systemId);
119         }
120     }
121 
122 
123     /* =========================================================================== */
124     /* CALL JING TO ACCESS A CACHED OR FRESHLY PARSED SCHEMA INSTANCE              */
125     /* =========================================================================== */
126 
127     /**
128      * <p>Create an {@link XMLReader} instance that can be used by
129      * <a HREF="http://www.thaiopensource.com/relaxng/jing.html">JING</a> for
130      * parsing schemas.</p>
131      * 
132      * <p>The returned {@link XMLReader} will keep track of populating/clearing the
133      * {@link Stack} of {@link InputSource}s kept for URI resolution as explained
134      * in the description of the {@link #resolveEntity(String, String)} method.</p>
135      * 
136      * @link JingReader
137      * @return a <b>non-null</b> {@link XMLReader} instance.
138      * @throws SAXException if an error occurrent creating the {@link XMLReader}.
139      */
140     public XMLReader   createXMLReader()
141     throws SAXException   {
142         return new JingReader(this);
143     }
144 }
145
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