001 /* XPathFactory.java --
002 Copyright (C) 2004, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
010
011 GNU Classpath is distributed in the hope that it will be useful, but
012 WITHOUT ANY WARRANTY; without even the implied warranty of
013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014 General Public License for more details.
015
016 You should have received a copy of the GNU General Public License
017 along with GNU Classpath; see the file COPYING. If not, write to the
018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
028 executable, regardless of the license terms of these independent
029 modules, and to copy and distribute the resulting executable under
030 terms of your choice, provided that you also meet, for each linked
031 independent module, the terms and conditions of the license of that
032 module. An independent module is a module which is not derived from
033 or based on this library. If you modify this library, you may extend
034 this exception to your version of the library, but you are not
035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038 package javax.xml.xpath;
039
040 import java.io.BufferedReader;
041 import java.io.File;
042 import java.io.FileInputStream;
043 import java.io.InputStream;
044 import java.io.InputStreamReader;
045 import java.io.IOException;
046 import java.util.Properties;
047
048 /**
049 * Factory for creating XPath environments.
050 *
051 * @author (a href='mailto:dog@gnu.org'>Chris Burdess</a)
052 * @since 1.3
053 */
054 public abstract class XPathFactory
055 {
056
057 /**
058 * The default property name according to the JAXP specification.
059 */
060 public static final String DEFAULT_PROPERTY_NAME =
061 "javax.xml.xpath.XPathFactory";
062
063 /**
064 * The default object model URI.
065 */
066 public static final String DEFAULT_OBJECT_MODEL_URI =
067 XPathConstants.DOM_OBJECT_MODEL;
068
069 protected XPathFactory()
070 {
071 }
072
073 /**
074 * Returns a new factory for the default (DOM) object model.
075 */
076 public static final XPathFactory newInstance()
077 {
078 try
079 {
080 return newInstance(DEFAULT_OBJECT_MODEL_URI);
081 }
082 catch (XPathFactoryConfigurationException e)
083 {
084 throw new RuntimeException(e.getMessage());
085 }
086 }
087
088 /**
089 * Returns a new factory for the given object model URI.
090 * The implementation class to load is the first found in the following
091 * locations that advertises support for the given model URI:
092 * <ol>
093 * <li>the <code>javax.xml.xpath.XPathFactory</code> system property</li>
094 * <li>the above named property value in the
095 * <code><i>$JAVA_HOME</i>/lib/jaxp.properties</code> file</li>
096 * <li>the class name specified in the
097 * <code>META-INF/services/javax.xml.xpath.XPathFactory</code> system
098 * resource</li>
099 * <li>the default factory class</li>
100 * </ol>
101 * @param uri the object model URI
102 */
103 public static final XPathFactory newInstance(String uri)
104 throws XPathFactoryConfigurationException
105 {
106 ClassLoader loader = Thread.currentThread().getContextClassLoader();
107 if (loader == null)
108 {
109 loader = XPathFactory.class.getClassLoader();
110 }
111 String className = null;
112 int count = 0;
113 do
114 {
115 className = getFactoryClassName(loader, count++);
116 if (className != null)
117 {
118 try
119 {
120 Class<?> t = (loader != null) ? loader.loadClass(className) :
121 Class.forName(className);
122 XPathFactory ret = (XPathFactory) t.newInstance();
123 if (ret.isObjectModelSupported(uri))
124 {
125 return ret;
126 }
127 className = null;
128 }
129 catch (ClassNotFoundException e)
130 {
131 className = null;
132 }
133 catch (Exception e)
134 {
135 throw new XPathFactoryConfigurationException(e);
136 }
137 }
138 }
139 while (className == null && count < 4);
140 String msg = "no factories with support for " + uri;
141 throw new XPathFactoryConfigurationException(msg);
142 }
143
144 private static String getFactoryClassName(ClassLoader loader, int attempt)
145 {
146 final String propertyName = DEFAULT_PROPERTY_NAME;
147 switch (attempt)
148 {
149 case 0:
150 return System.getProperty(propertyName);
151 case 1:
152 try
153 {
154 File file = new File(System.getProperty("java.home"));
155 file = new File(file, "lib");
156 file = new File(file, "jaxp.properties");
157 InputStream in = new FileInputStream(file);
158 Properties props = new Properties();
159 props.load(in);
160 in.close();
161 return props.getProperty(propertyName);
162 }
163 catch (IOException e)
164 {
165 return null;
166 }
167 case 2:
168 try
169 {
170 String serviceKey = "/META-INF/services/" + propertyName;
171 InputStream in = (loader != null) ?
172 loader.getResourceAsStream(serviceKey) :
173 XPathFactory.class.getResourceAsStream(serviceKey);
174 if (in != null)
175 {
176 BufferedReader r =
177 new BufferedReader(new InputStreamReader(in));
178 String ret = r.readLine();
179 r.close();
180 return ret;
181 }
182 }
183 catch (IOException e)
184 {
185 }
186 return null;
187 case 3:
188 return "gnu.xml.xpath.XPathFactoryImpl";
189 default:
190 return null;
191 }
192 }
193
194 /**
195 * Indicates whether the specified object model URI is supported by
196 * this factory.
197 */
198 public abstract boolean isObjectModelSupported(String objectModel);
199
200 /**
201 * Sets the state of the named feature.
202 */
203 public abstract void setFeature(String name, boolean value)
204 throws XPathFactoryConfigurationException;
205
206 /**
207 * Returns the state of the named feature.
208 */
209 public abstract boolean getFeature(String name)
210 throws XPathFactoryConfigurationException;
211
212 /**
213 * Sets the XPath variable resolver calback.
214 */
215 public abstract void setXPathVariableResolver(XPathVariableResolver resolver);
216
217 /**
218 * Sets the XPath extension function resolver calback.
219 */
220 public abstract void setXPathFunctionResolver(XPathFunctionResolver resolver);
221
222 /**
223 * Returns a new XPath evaluation environment.
224 */
225 public abstract XPath newXPath();
226
227 }