1 // XMLReaderFactory.java - factory for creating a new reader. 2 // http://www.saxproject.org 3 // Written by David Megginson 4 // and by David Brownell 5 // NO WARRANTY! This class is in the Public Domain. 6 // $Id: XMLReaderFactory.java,v 1.10 2002/04/22 01:00:13 dbrownell Exp $ 7 8 package org.xml.sax.helpers; 9 10 import java.io.BufferedReader; 11 import java.io.InputStream; 12 import java.io.InputStreamReader; 13 import java.nio.charset.StandardCharsets; 14 import org.xml.sax.SAXException; 15 import org.xml.sax.XMLReader; 16 17 18 /** 19 * Factory for creating an XML reader. 20 * 21 * <blockquote> 22 * <em>This module, both source code and documentation, is in the 23 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em> 24 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a> 25 * for further information. 26 * </blockquote> 27 * 28 * <p>This class contains static methods for creating an XML reader 29 * from an explicit class name, or based on runtime defaults:</p> 30 * 31 * <pre> 32 * try { 33 * XMLReader myReader = XMLReaderFactory.createXMLReader(); 34 * } catch (SAXException e) { 35 * System.err.println(e.getMessage()); 36 * } 37 * </pre> 38 * 39 * <p><strong>Note to Distributions bundled with parsers:</strong> 40 * You should modify the implementation of the no-arguments 41 * <em>createXMLReader</em> to handle cases where the external 42 * configuration mechanisms aren't set up. That method should do its 43 * best to return a parser when one is in the class path, even when 44 * nothing bound its class name to <code>org.xml.sax.driver</code> so 45 * those configuration mechanisms would see it.</p> 46 * 47 * @since SAX 2.0 48 * @author David Megginson, David Brownell 49 * @version 2.0.1 (sax2r2) 50 */ 51 final public class XMLReaderFactory 52 { 53 /** 54 * Private constructor. 55 * 56 * <p>This constructor prevents the class from being instantiated.</p> 57 */ XMLReaderFactory()58 private XMLReaderFactory () 59 { 60 } 61 62 private static final String property = "org.xml.sax.driver"; 63 64 /** 65 * Attempt to create an XMLReader from system defaults. 66 * In environments which can support it, the name of the XMLReader 67 * class is determined by trying each these options in order, and 68 * using the first one which succeeds:</p> <ul> 69 * 70 * <li>If the system property <code>org.xml.sax.driver</code> 71 * has a value, that is used as an XMLReader class name. </li> 72 * 73 * <li>The JAR "Services API" is used to look for a class name 74 * in the <em>META-INF/services/org.xml.sax.driver</em> file in 75 * jarfiles available to the runtime.</li> 76 * 77 * <li> SAX parser distributions are strongly encouraged to provide 78 * a default XMLReader class name that will take effect only when 79 * previous options (on this list) are not successful.</li> 80 * 81 * <li>Finally, if {@link ParserFactory#makeParser()} can 82 * return a system default SAX1 parser, that parser is wrapped in 83 * a {@link ParserAdapter}. (This is a migration aid for SAX1 84 * environments, where the <code>org.xml.sax.parser</code> system 85 * property will often be usable.) </li> 86 * 87 * </ul> 88 * 89 * <p> In environments such as small embedded systems, which can not 90 * support that flexibility, other mechanisms to determine the default 91 * may be used. </p> 92 * 93 * <p>Note that many Java environments allow system properties to be 94 * initialized on a command line. This means that <em>in most cases</em> 95 * setting a good value for that property ensures that calls to this 96 * method will succeed, except when security policies intervene. 97 * This will also maximize application portability to older SAX 98 * environments, with less robust implementations of this method. 99 * </p> 100 * 101 * @return A new XMLReader. 102 * @exception org.xml.sax.SAXException If no default XMLReader class 103 * can be identified and instantiated. 104 * @see #createXMLReader(java.lang.String) 105 */ createXMLReader()106 public static XMLReader createXMLReader () 107 throws SAXException 108 { 109 String className = null; 110 ClassLoader loader = NewInstance.getClassLoader (); 111 112 // 1. try the JVM-instance-wide system property 113 try { className = System.getProperty (property); } 114 catch (RuntimeException e) { /* normally fails for applets */ } 115 116 // 2. if that fails, try META-INF/services/ 117 if (className == null) { 118 try { 119 String service = "META-INF/services/" + property; 120 InputStream in; 121 BufferedReader reader; 122 123 if (loader == null) 124 in = ClassLoader.getSystemResourceAsStream (service); 125 else 126 in = loader.getResourceAsStream (service); 127 128 if (in != null) { 129 reader = new BufferedReader (new InputStreamReader (in, StandardCharsets.UTF_8)); 130 className = reader.readLine (); 131 in.close (); 132 } 133 } catch (Exception e) { 134 } 135 } 136 137 // 3. Distro-specific fallback 138 if (className == null) { 139 // BEGIN DISTRIBUTION-SPECIFIC 140 141 // EXAMPLE: 142 // className = "com.example.sax.XmlReader"; 143 // or a $JAVA_HOME/jre/lib/*properties setting... 144 145 // END DISTRIBUTION-SPECIFIC 146 } 147 148 // do we know the XMLReader implementation class yet? 149 if (className != null) 150 return loadClass (loader, className); 151 152 // 4. panic -- adapt any SAX1 parser 153 try { 154 return new ParserAdapter (ParserFactory.makeParser ()); 155 } catch (Exception e) { 156 throw new SAXException ("Can't create default XMLReader; " 157 + "is system property org.xml.sax.driver set?"); 158 } 159 } 160 161 162 /** 163 * Attempt to create an XML reader from a class name. 164 * 165 * <p>Given a class name, this method attempts to load 166 * and instantiate the class as an XML reader.</p> 167 * 168 * @param className the name of the class that should be instantiated. 169 * 170 * <p>Note that this method will not be usable in environments where 171 * the caller (perhaps an applet) is not permitted to load classes 172 * dynamically.</p> 173 * 174 * @return A new XML reader. 175 * @exception org.xml.sax.SAXException If the class cannot be 176 * loaded, instantiated, and cast to XMLReader. 177 * @see #createXMLReader() 178 */ createXMLReader(String className)179 public static XMLReader createXMLReader (String className) 180 throws SAXException 181 { 182 return loadClass (NewInstance.getClassLoader (), className); 183 } 184 loadClass(ClassLoader loader, String className)185 private static XMLReader loadClass (ClassLoader loader, String className) 186 throws SAXException 187 { 188 try { 189 return (XMLReader) NewInstance.newInstance (loader, className); 190 } catch (ClassNotFoundException e1) { 191 throw new SAXException("SAX2 driver class " + className + 192 " not found", e1); 193 } catch (IllegalAccessException e2) { 194 throw new SAXException("SAX2 driver class " + className + 195 " found but cannot be loaded", e2); 196 } catch (InstantiationException e3) { 197 throw new SAXException("SAX2 driver class " + className + 198 " loaded but cannot be instantiated (no empty public constructor?)", 199 e3); 200 } catch (ClassCastException e4) { 201 throw new SAXException("SAX2 driver class " + className + 202 " does not implement XMLReader", e4); 203 } 204 } 205 } 206