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 org.xml.sax.SAXException; 11 import org.xml.sax.XMLReader; 12 13 import android.compat.annotation.UnsupportedAppUsage; 14 15 import java.io.BufferedReader; 16 import java.io.InputStream; 17 import java.io.InputStreamReader; 18 import java.nio.charset.StandardCharsets; 19 20 21 /** 22 * Factory for creating an XML reader. 23 * 24 * <blockquote> 25 * <em>This module, both source code and documentation, is in the 26 * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em> 27 * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a> 28 * for further information. 29 * </blockquote> 30 * 31 * <p>This class contains static methods for creating an XML reader 32 * from an explicit class name, or based on runtime defaults:</p> 33 * 34 * <pre> 35 * try { 36 * XMLReader myReader = XMLReaderFactory.createXMLReader(); 37 * } catch (SAXException e) { 38 * System.err.println(e.getMessage()); 39 * } 40 * </pre> 41 * 42 * <p><strong>Note to Distributions bundled with parsers:</strong> 43 * You should modify the implementation of the no-arguments 44 * <em>createXMLReader</em> to handle cases where the external 45 * configuration mechanisms aren't set up. That method should do its 46 * best to return a parser when one is in the class path, even when 47 * nothing bound its class name to <code>org.xml.sax.driver</code> so 48 * those configuration mechanisms would see it.</p> 49 * 50 * @since SAX 2.0 51 * @author David Megginson, David Brownell 52 * @version 2.0.1 (sax2r2) 53 */ 54 final public class XMLReaderFactory 55 { 56 /** 57 * Private constructor. 58 * 59 * <p>This constructor prevents the class from being instantiated.</p> 60 */ XMLReaderFactory()61 private XMLReaderFactory () 62 { 63 } 64 65 private static final String property = "org.xml.sax.driver"; 66 67 /** 68 * Attempt to create an XMLReader from system defaults. 69 * In environments which can support it, the name of the XMLReader 70 * class is determined by trying each these options in order, and 71 * using the first one which succeeds:</p> <ul> 72 * 73 * <li>If the system property <code>org.xml.sax.driver</code> 74 * has a value, that is used as an XMLReader class name. </li> 75 * 76 * <li>The JAR "Services API" is used to look for a class name 77 * in the <em>META-INF/services/org.xml.sax.driver</em> file in 78 * jarfiles available to the runtime.</li> 79 * 80 * <li> SAX parser distributions are strongly encouraged to provide 81 * a default XMLReader class name that will take effect only when 82 * previous options (on this list) are not successful.</li> 83 * 84 * <li>Finally, if {@link ParserFactory#makeParser()} can 85 * return a system default SAX1 parser, that parser is wrapped in 86 * a {@link ParserAdapter}. (This is a migration aid for SAX1 87 * environments, where the <code>org.xml.sax.parser</code> system 88 * property will often be usable.) </li> 89 * 90 * </ul> 91 * 92 * <p> In environments such as small embedded systems, which can not 93 * support that flexibility, other mechanisms to determine the default 94 * may be used. </p> 95 * 96 * <p>Note that many Java environments allow system properties to be 97 * initialized on a command line. This means that <em>in most cases</em> 98 * setting a good value for that property ensures that calls to this 99 * method will succeed, except when security policies intervene. 100 * This will also maximize application portability to older SAX 101 * environments, with less robust implementations of this method. 102 * </p> 103 * 104 * @return A new XMLReader. 105 * @exception org.xml.sax.SAXException If no default XMLReader class 106 * can be identified and instantiated. 107 * @see #createXMLReader(java.lang.String) 108 */ createXMLReader()109 public static XMLReader createXMLReader () 110 throws SAXException 111 { 112 String className = null; 113 ClassLoader loader = NewInstance.getClassLoader (); 114 115 // 1. try the JVM-instance-wide system property 116 try { className = System.getProperty (property); } 117 catch (RuntimeException e) { /* normally fails for applets */ } 118 119 // 2. if that fails, try META-INF/services/ 120 if (className == null) { 121 try { 122 String service = "META-INF/services/" + property; 123 InputStream in; 124 BufferedReader reader; 125 126 if (loader == null) 127 in = ClassLoader.getSystemResourceAsStream (service); 128 else 129 in = loader.getResourceAsStream (service); 130 131 if (in != null) { 132 try { 133 reader = new BufferedReader(new InputStreamReader(in, StandardCharsets.UTF_8)); 134 className = reader.readLine(); 135 } finally { 136 in.close(); // may throw IOException 137 } 138 } 139 } catch (Exception e) { 140 } 141 } 142 143 // 3. Distro-specific fallback 144 if (className == null) { 145 // BEGIN DISTRIBUTION-SPECIFIC 146 147 // EXAMPLE: 148 // className = "com.example.sax.XmlReader"; 149 // or a $JAVA_HOME/jre/lib/*properties setting... 150 151 // END DISTRIBUTION-SPECIFIC 152 } 153 154 // do we know the XMLReader implementation class yet? 155 if (className != null) 156 return loadClass (loader, className); 157 158 // 4. panic -- adapt any SAX1 parser 159 try { 160 return new ParserAdapter (ParserFactory.makeParser ()); 161 } catch (Exception e) { 162 throw new SAXException ("Can't create default XMLReader; " 163 + "is system property org.xml.sax.driver set?"); 164 } 165 } 166 167 168 /** 169 * Attempt to create an XML reader from a class name. 170 * 171 * <p>Given a class name, this method attempts to load 172 * and instantiate the class as an XML reader.</p> 173 * 174 * @param className the name of the class that should be instantiated. 175 * 176 * <p>Note that this method will not be usable in environments where 177 * the caller (perhaps an applet) is not permitted to load classes 178 * dynamically.</p> 179 * 180 * @return A new XML reader. 181 * @exception org.xml.sax.SAXException If the class cannot be 182 * loaded, instantiated, and cast to XMLReader. 183 * @see #createXMLReader() 184 */ createXMLReader(String className)185 public static XMLReader createXMLReader (String className) 186 throws SAXException 187 { 188 return loadClass (NewInstance.getClassLoader (), className); 189 } 190 191 @UnsupportedAppUsage loadClass(ClassLoader loader, String className)192 private static XMLReader loadClass (ClassLoader loader, String className) 193 throws SAXException 194 { 195 try { 196 return (XMLReader) NewInstance.newInstance (loader, className); 197 } catch (ClassNotFoundException e1) { 198 throw new SAXException("SAX2 driver class " + className + 199 " not found", e1); 200 } catch (IllegalAccessException e2) { 201 throw new SAXException("SAX2 driver class " + className + 202 " found but cannot be loaded", e2); 203 } catch (InstantiationException e3) { 204 throw new SAXException("SAX2 driver class " + className + 205 " loaded but cannot be instantiated (no empty public constructor?)", 206 e3); 207 } catch (ClassCastException e4) { 208 throw new SAXException("SAX2 driver class " + className + 209 " does not implement XMLReader", e4); 210 } 211 } 212 } 213