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ObjectFactory.javaAPI DocJava SE 5 API20997Fri Aug 26 14:56:02 BST 2005com.sun.org.apache.xml.internal.serialize

ObjectFactory

public class ObjectFactory extends Object
This class is duplicated for each JAXP subpackage so keep it in sync. It is package private and therefore is not exposed as part of the JAXP API.

This code is designed to implement the JAXP 1.1 spec pluggability feature and is designed to run on JDK version 1.1 and later, and to compile on JDK 1.2 and onward. The code also runs both as part of an unbundled jar file and when bundled as part of the JDK.

version
$Id: ObjectFactory.java,v 1.2 2004/05/08 07:21:18 vk112360 Exp $

Fields Summary
private static final String
DEFAULT_PROPERTIES_FILENAME
private static final boolean
DEBUG
Set to true for debugging
private static Properties
fXercesProperties
cache the contents of the xerces.properties file. Until an attempt has been made to read this file, this will be null; if the file does not exist or we encounter some other error during the read, this will be empty.
private static long
fLastModified
Cache the time stamp of the xerces.properties file so that we know if it's been modified and can invalidate the cache when necessary.
Constructors Summary
Methods Summary
static java.lang.ObjectcreateObject(java.lang.String factoryId, java.lang.String fallbackClassName)
Finds the implementation Class object in the specified order. The specified order is the following:
  1. query the system property using System.getProperty
  2. read META-INF/services/factoryId file
  3. use fallback classname

return
Class object of factory, never null
param
factoryId Name of the factory to find, same as a property name
param
fallbackClassName Implementation class name, if nothing else is found. Use null to mean no fallback.
exception
ObjectFactory.ConfigurationError


    //
    // static methods
    //

                                                                                                                                                           
         
          
        return createObject(factoryId, null, fallbackClassName);
static java.lang.ObjectcreateObject(java.lang.String factoryId, java.lang.String propertiesFilename, java.lang.String fallbackClassName)
Finds the implementation Class object in the specified order. The specified order is the following:
  1. query the system property using System.getProperty
  2. read $java.home/lib/propertiesFilename file
  3. read META-INF/services/factoryId file
  4. use fallback classname

return
Class object of factory, never null
param
factoryId Name of the factory to find, same as a property name
param
propertiesFilename The filename in the $java.home/lib directory of the properties file. If none specified, ${java.home}/lib/xerces.properties will be used.
param
fallbackClassName Implementation class name, if nothing else is found. Use null to mean no fallback.
exception
ObjectFactory.ConfigurationError

        if (DEBUG) debugPrintln("debug is on");

        SecuritySupport ss = SecuritySupport.getInstance();
        ClassLoader cl = findClassLoader();

        // Use the system property first
        try {
            String systemProp = ss.getSystemProperty(factoryId);
            if (systemProp != null) {
                if (DEBUG) debugPrintln("found system property, value=" + systemProp);
                return newInstance(systemProp, cl, true);
            }
        } catch (SecurityException se) {
            // Ignore and continue w/ next location
        }

        // Try to read from propertiesFilename, or $java.home/lib/xerces.properties
        String factoryClassName = null;
        // no properties file name specified; use $JAVA_HOME/lib/xerces.properties:
        if (propertiesFilename == null) {
            File propertiesFile = null;
            boolean propertiesFileExists = false;
            try {
                String javah = ss.getSystemProperty("java.home");
                propertiesFilename = javah + File.separator +
                    "lib" + File.separator + DEFAULT_PROPERTIES_FILENAME;
                propertiesFile = new File(propertiesFilename);
                propertiesFileExists = ss.getFileExists(propertiesFile);
            } catch (SecurityException e) {
                // try again...
                fLastModified = -1;
                fXercesProperties = null;
            }

            synchronized (ObjectFactory.class) {
                boolean loadProperties = false;
                try {
                    // file existed last time
                    if(fLastModified >= 0) {
                        if(propertiesFileExists &&
                                (fLastModified < (fLastModified = ss.getLastModified(propertiesFile)))) {
                            loadProperties = true;
                        } else {
                            // file has stopped existing...
                            if(!propertiesFileExists) {
                                fLastModified = -1;
                                fXercesProperties = null;
                            } // else, file wasn't modified!
                        }
                    } else {
                        // file has started to exist:
                        if(propertiesFileExists) {
                            loadProperties = true;
                            fLastModified = ss.getLastModified(propertiesFile);
                        } // else, nothing's changed
                    }
                    if(loadProperties) {
                        // must never have attempted to read xerces.properties before (or it's outdeated)
                        fXercesProperties = new Properties();
                        FileInputStream fis = ss.getFileInputStream(propertiesFile);
                        fXercesProperties.load(fis);
                        fis.close();
                    }
	            } catch (Exception x) {
	                fXercesProperties = null;
	                fLastModified = -1;
                    // assert(x instanceof FileNotFoundException
	                //        || x instanceof SecurityException)
	                // In both cases, ignore and continue w/ next location
	            }
            }
            if(fXercesProperties != null) {
                factoryClassName = fXercesProperties.getProperty(factoryId);
            }
        } else {
            try {
                FileInputStream fis = ss.getFileInputStream(new File(propertiesFilename));
                Properties props = new Properties();
                props.load(fis);
                fis.close();
                factoryClassName = props.getProperty(factoryId);
            } catch (Exception x) {
                // assert(x instanceof FileNotFoundException
                //        || x instanceof SecurityException)
                // In both cases, ignore and continue w/ next location
            }
        }
        if (factoryClassName != null) {
            if (DEBUG) debugPrintln("found in " + propertiesFilename + ", value=" + factoryClassName);
            return newInstance(factoryClassName, cl, true);
        }

        // Try Jar Service Provider Mechanism
        Object provider = findJarServiceProvider(factoryId);
        if (provider != null) {
            return provider;
        }

        if (fallbackClassName == null) {
            throw new ConfigurationError(
                "Provider for " + factoryId + " cannot be found", null);
        }

        if (DEBUG) debugPrintln("using fallback, value=" + fallbackClassName);
        return newInstance(fallbackClassName, cl, true);
private static voiddebugPrintln(java.lang.String msg)
Prints a message to standard error if debugging is enabled.

        if (DEBUG) {
            System.err.println("JAXP: " + msg);
        }
static java.lang.ClassLoaderfindClassLoader()
Figure out which ClassLoader to use. For JDK 1.2 and later use the context ClassLoader.

        SecuritySupport ss = SecuritySupport.getInstance();

        // Figure out which ClassLoader to use for loading the provider
        // class.  If there is a Context ClassLoader then use it.
        ClassLoader context = ss.getContextClassLoader();
        ClassLoader system = ss.getSystemClassLoader();

        ClassLoader chain = system;
        while (true) {
            if (context == chain) {
                // Assert: we are on JDK 1.1 or we have no Context ClassLoader
                // or any Context ClassLoader in chain of system classloader
                // (including extension ClassLoader) so extend to widest
                // ClassLoader (always look in system ClassLoader if Xerces
                // is in boot/extension/system classpath and in current
                // ClassLoader otherwise); normal classloaders delegate
                // back to system ClassLoader first so this widening doesn't
                // change the fact that context ClassLoader will be consulted
                ClassLoader current = ObjectFactory.class.getClassLoader();

                chain = system;
                while (true) {
                    if (current == chain) {
                        // Assert: Current ClassLoader in chain of
                        // boot/extension/system ClassLoaders
                        return system;
                    }
                    if (chain == null) {
                        break;
                    }
                    chain = ss.getParentClassLoader(chain);
                }

                // Assert: Current ClassLoader not in chain of
                // boot/extension/system ClassLoaders
                return current;
            }

            if (chain == null) {
                // boot ClassLoader reached
                break;
            }

            // Check for any extension ClassLoaders in chain up to
            // boot ClassLoader
            chain = ss.getParentClassLoader(chain);
        };

        // Assert: Context ClassLoader not in chain of
        // boot/extension/system ClassLoaders
        return context;
private static java.lang.ObjectfindJarServiceProvider(java.lang.String factoryId)

        SecuritySupport ss = SecuritySupport.getInstance();
        String serviceId = "META-INF/services/" + factoryId;
        InputStream is = null;

        // First try the Context ClassLoader
        ClassLoader cl = findClassLoader();

        is = ss.getResourceAsStream(cl, serviceId);

        // If no provider found then try the current ClassLoader
        if (is == null) {
            ClassLoader current = ObjectFactory.class.getClassLoader();
            if (cl != current) {
                cl = current;
                is = ss.getResourceAsStream(cl, serviceId);
            }
        }

        if (is == null) {
            // No provider found
            return null;
        }

        if (DEBUG) debugPrintln("found jar resource=" + serviceId +
               " using ClassLoader: " + cl);

        // Read the service provider name in UTF-8 as specified in
        // the jar spec.  Unfortunately this fails in Microsoft
        // VJ++, which does not implement the UTF-8
        // encoding. Theoretically, we should simply let it fail in
        // that case, since the JVM is obviously broken if it
        // doesn't support such a basic standard.  But since there
        // are still some users attempting to use VJ++ for
        // development, we have dropped in a fallback which makes a
        // second attempt using the platform's default encoding. In
        // VJ++ this is apparently ASCII, which is a subset of
        // UTF-8... and since the strings we'll be reading here are
        // also primarily limited to the 7-bit ASCII range (at
        // least, in English versions), this should work well
        // enough to keep us on the air until we're ready to
        // officially decommit from VJ++. [Edited comment from
        // jkesselm]
        BufferedReader rd;
        try {
            rd = new BufferedReader(new InputStreamReader(is, "UTF-8"));
        } catch (java.io.UnsupportedEncodingException e) {
            rd = new BufferedReader(new InputStreamReader(is));
        }

        String factoryClassName = null;
        try {
            // XXX Does not handle all possible input as specified by the
            // Jar Service Provider specification
            factoryClassName = rd.readLine();
            rd.close();
        } catch (IOException x) {
            // No provider found
            return null;
        }

        if (factoryClassName != null &&
            ! "".equals(factoryClassName)) {
            if (DEBUG) debugPrintln("found in resource, value="
                   + factoryClassName);

            // Note: here we do not want to fall back to the current
            // ClassLoader because we want to avoid the case where the
            // resource file was found using one ClassLoader and the
            // provider class was instantiated using a different one.
            return newInstance(factoryClassName, cl, false);
        }

        // No provider found
        return null;
static java.lang.ClassfindProviderClass(java.lang.String className, java.lang.ClassLoader cl, boolean doFallback)
Find a Class using the specified ClassLoader

        //throw security exception if the calling thread is not allowed to access the package
        //restrict the access to package as speicified in java.security policy
        SecurityManager security = System.getSecurityManager();
        try{
            if(security != null){
                security.checkPackageAccess(className);
            }
        }catch(SecurityException e){
            throw e ;
        }
        Class providerClass;
        if (cl == null) {
            // XXX Use the bootstrap ClassLoader.  There is no way to
            // load a class using the bootstrap ClassLoader that works
            // in both JDK 1.1 and Java 2.  However, this should still
            // work b/c the following should be true:
            //
            // (cl == null) iff current ClassLoader == null
            //
            // Thus Class.forName(String) will use the current
            // ClassLoader which will be the bootstrap ClassLoader.
            providerClass = Class.forName(className);
        } else {
            try {
                providerClass = cl.loadClass(className);
            } catch (ClassNotFoundException x) {
                if (doFallback) {
                    // Fall back to current classloader
                    ClassLoader current = ObjectFactory.class.getClassLoader();
                    if (current == null) {
                        providerClass = Class.forName(className);
                    } else if (cl != current) {
                        cl = current;
                        providerClass = cl.loadClass(className);
                    } else {
                        throw x;
                    }
                } else {
                    throw x;
                }
            }
        }

        return providerClass;
static java.lang.ObjectnewInstance(java.lang.String className, java.lang.ClassLoader cl, boolean doFallback)
Create an instance of a class using the specified ClassLoader

        // assert(className != null);
        try{
            Class providerClass = findProviderClass(className, cl, doFallback);
            Object instance = providerClass.newInstance();
            if (DEBUG) debugPrintln("created new instance of " + providerClass +
                   " using ClassLoader: " + cl);
            return instance;
        } catch (ClassNotFoundException x) {
            throw new ConfigurationError(
                "Provider " + className + " not found", x);
        } catch (Exception x) {
            throw new ConfigurationError(
                "Provider " + className + " could not be instantiated: " + x,
                x);
        }