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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 1.1 2004/12/23 22:38:42 mark Exp $ 7: 8: package org.xml.sax.helpers; 9: import java.io.BufferedReader; 10: import java.io.InputStream; 11: import java.io.InputStreamReader; 12: import org.xml.sax.XMLReader; 13: import org.xml.sax.SAXException; 14: 15: 16: /** 17: * Factory for creating an XML reader. 18: * 19: * <blockquote> 20: * <em>This module, both source code and documentation, is in the 21: * Public Domain, and comes with <strong>NO WARRANTY</strong>.</em> 22: * See <a href='http://www.saxproject.org'>http://www.saxproject.org</a> 23: * for further information. 24: * </blockquote> 25: * 26: * <p>This class contains static methods for creating an XML reader 27: * from an explicit class name, or based on runtime defaults:</p> 28: * 29: * <pre> 30: * try { 31: * XMLReader myReader = XMLReaderFactory.createXMLReader(); 32: * } catch (SAXException e) { 33: * System.err.println(e.getMessage()); 34: * } 35: * </pre> 36: * 37: * <p><strong>Note to Distributions bundled with parsers:</strong> 38: * You should modify the implementation of the no-arguments 39: * <em>createXMLReader</em> to handle cases where the external 40: * configuration mechanisms aren't set up. That method should do its 41: * best to return a parser when one is in the class path, even when 42: * nothing bound its class name to <code>org.xml.sax.driver</code> so 43: * those configuration mechanisms would see it.</p> 44: * 45: * @since SAX 2.0 46: * @author David Megginson, David Brownell 47: * @version 2.0.1 (sax2r2) 48: */ 49: final public class XMLReaderFactory 50: { 51: /** 52: * Private constructor. 53: * 54: * <p>This constructor prevents the class from being instantiated.</p> 55: */ 56: private XMLReaderFactory () 57: { 58: } 59: 60: private static final String property = "org.xml.sax.driver"; 61: 62: /** 63: * Attempt to create an XMLReader from system defaults. 64: * In environments which can support it, the name of the XMLReader 65: * class is determined by trying each these options in order, and 66: * using the first one which succeeds:</p> <ul> 67: * 68: * <li>If the system property <code>org.xml.sax.driver</code> 69: * has a value, that is used as an XMLReader class name. </li> 70: * 71: * <li>The JAR "Services API" is used to look for a class name 72: * in the <em>META-INF/services/org.xml.sax.driver</em> file in 73: * jarfiles available to the runtime.</li> 74: * 75: * <li> SAX parser distributions are strongly encouraged to provide 76: * a default XMLReader class name that will take effect only when 77: * previous options (on this list) are not successful.</li> 78: * 79: * <li>Finally, if {@link ParserFactory#makeParser()} can 80: * return a system default SAX1 parser, that parser is wrapped in 81: * a {@link ParserAdapter}. (This is a migration aid for SAX1 82: * environments, where the <code>org.xml.sax.parser</code> system 83: * property will often be usable.) </li> 84: * 85: * </ul> 86: * 87: * <p> In environments such as small embedded systems, which can not 88: * support that flexibility, other mechanisms to determine the default 89: * may be used. </p> 90: * 91: * <p>Note that many Java environments allow system properties to be 92: * initialized on a command line. This means that <em>in most cases</em> 93: * setting a good value for that property ensures that calls to this 94: * method will succeed, except when security policies intervene. 95: * This will also maximize application portability to older SAX 96: * environments, with less robust implementations of this method. 97: * </p> 98: * 99: * @return A new XMLReader. 100: * @exception org.xml.sax.SAXException If no default XMLReader class 101: * can be identified and instantiated. 102: * @see #createXMLReader(java.lang.String) 103: */ 104: public static XMLReader createXMLReader () 105: throws SAXException 106: { 107: String className = null; 108: ClassLoader loader = NewInstance.getClassLoader (); 109: 110: // 1. try the JVM-instance-wide system property 111: try { className = System.getProperty (property); } 112: catch (RuntimeException e) { /* normally fails for applets */ } 113: 114: // 2. if that fails, try META-INF/services/ 115: if (className == null) { 116: try { 117: String service = "META-INF/services/" + property; 118: InputStream in; 119: BufferedReader reader; 120: 121: if (loader == null) 122: in = ClassLoader.getSystemResourceAsStream (service); 123: else 124: in = loader.getResourceAsStream (service); 125: 126: if (in != null) { 127: reader = new BufferedReader ( 128: new InputStreamReader (in, "UTF8")); 129: className = reader.readLine (); 130: in.close (); 131: } 132: } catch (Exception e) { 133: } 134: } 135: 136: // 3. Distro-specific fallback 137: if (className == null) { 138: // BEGIN DISTRIBUTION-SPECIFIC 139: 140: // CLASSPATH LOCAL: have to code in the backup. 141: // Among other things, see PR 31303, and this thread: 142: // http://gcc.gnu.org/ml/java-patches/2007-q1/msg00661.html 143: className = "gnu.xml.stream.SAXParser"; 144: 145: // EXAMPLE: 146: // className = "com.example.sax.XmlReader"; 147: // or a $JAVA_HOME/jre/lib/*properties setting... 148: 149: // END DISTRIBUTION-SPECIFIC 150: } 151: 152: // do we know the XMLReader implementation class yet? 153: if (className != null) 154: return loadClass (loader, className); 155: 156: // 4. panic -- adapt any SAX1 parser 157: try { 158: return new ParserAdapter (ParserFactory.makeParser ()); 159: } catch (Exception e) { 160: throw new SAXException ("Can't create default XMLReader; " 161: + "is system property org.xml.sax.driver set?"); 162: } 163: } 164: 165: 166: /** 167: * Attempt to create an XML reader from a class name. 168: * 169: * <p>Given a class name, this method attempts to load 170: * and instantiate the class as an XML reader.</p> 171: * 172: * <p>Note that this method will not be usable in environments where 173: * the caller (perhaps an applet) is not permitted to load classes 174: * dynamically.</p> 175: * 176: * @return A new XML reader. 177: * @exception org.xml.sax.SAXException If the class cannot be 178: * loaded, instantiated, and cast to XMLReader. 179: * @see #createXMLReader() 180: */ 181: public static XMLReader createXMLReader (String className) 182: throws SAXException 183: { 184: return loadClass (NewInstance.getClassLoader (), className); 185: } 186: 187: private static XMLReader loadClass (ClassLoader loader, String className) 188: throws SAXException 189: { 190: try { 191: return (XMLReader) NewInstance.newInstance (loader, className); 192: } catch (ClassNotFoundException e1) { 193: throw new SAXException("SAX2 driver class " + className + 194: " not found", e1); 195: } catch (IllegalAccessException e2) { 196: throw new SAXException("SAX2 driver class " + className + 197: " found but cannot be loaded", e2); 198: } catch (InstantiationException e3) { 199: throw new SAXException("SAX2 driver class " + className + 200: " loaded but cannot be instantiated (no empty public constructor?)", 201: e3); 202: } catch (ClassCastException e4) { 203: throw new SAXException("SAX2 driver class " + className + 204: " does not implement XMLReader", e4); 205: } 206: } 207: }