ojluni/src/main/java/sun/security/jgss/ProviderList.java - platform/libcore.git - Git at Google

 /*
  * Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.  Oracle designates this
  * particular file as subject to the "Classpath" exception as provided
  * by Oracle in the LICENSE file that accompanied this code.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  */

 package sun.security.jgss;

 import java.lang.reflect.InvocationTargetException;
 import org.ietf.jgss.*;
 import java.security.AccessController;
 import java.security.Provider;
 import java.security.Security;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.HashMap;
 import java.util.Enumeration;
 import java.util.Iterator;
 import sun.security.jgss.spi.*;
 import sun.security.jgss.wrapper.NativeGSSFactory;
 import sun.security.jgss.wrapper.SunNativeProvider;
 import sun.security.action.GetPropertyAction;

 /**
  * This class stores the list of providers that this
  * GSS-Implementation is configured to use. The GSSManagerImpl class
  * queries this class whenever it needs a mechanism's factory.<p>
  *
  * This class stores an ordered list of pairs of the form
  * <provider, oid>. When it attempts to instantiate a mechanism
  * defined by oid o, it steps through the list looking for an entry
  * with oid=o, or with oid=null. (An entry with oid=null matches all
  * mechanisms.) When it finds such an entry, the corresponding
  * provider is approached for the mechanism's factory class.
  * At instantiation time this list in initialized to contain those
  * system wide providers that contain a property of the form
  * "GssApiMechanism.x.y.z..." where "x.y.z..." is a numeric object
  * identifier with numbers x, y, z, etc. Such a property is defined
  * to map to that provider's implementation of the MechanismFactory
  * interface for the mechanism x.y.z...
  * As and when a MechanismFactory is instantiated, it is
  * cached for future use. <p>
  *
  * An application can cause more providers to be added by means of
  * the addProviderAtFront and addProviderAtEnd methods on
  * GSSManager which get delegated to this class. The
  * addProviderAtFront method can also cause a change in the ordering
  * of the providers without adding any new providers, by causing a
  * provider to move up in a list. The method addProviderAtEnd can
  * only add providers at the end of the list if they are not already
  * in the list. The rationale is that an application will call
  * addProviderAtFront when it wants a provider to be used in
  * preference over the default ones. And it will call
  * addProviderAtEnd when it wants a provider to be used in case
  * the system ones don't suffice.<p>
  *
  * If a mechanism's factory is being obtained from a provider as a
  * result of encountering a entryof the form <provider, oid> where
  * oid is non-null, then the assumption is that the application added
  * this entry and it wants this mechanism to be obtained from this
  * provider. Thus is the provider does not actually contain the
  * requested mechanism, an exception will be thrown. However, if the
  * entry were of the form <provider, null>, then it is viewed more
  * liberally and is simply skipped over if the provider does not claim to
  * support the requested mechanism.
  */

 public final class ProviderList {

     private static final String PROV_PROP_PREFIX = "GssApiMechanism.";
     private static final int PROV_PROP_PREFIX_LEN =
         PROV_PROP_PREFIX.length();

     private static final String SPI_MECH_FACTORY_TYPE
         = "sun.security.jgss.spi.MechanismFactory";

     // Undocumented property?
     private static final String DEFAULT_MECH_PROP =
         "sun.security.jgss.mechanism";

     public static final Oid DEFAULT_MECH_OID;

     static {
         /*
          * Set the default mechanism. Kerberos v5 is the default
          * mechanism unless it is overridden by a system property.
          * with a valid OID value
          */
         Oid defOid = null;
         String defaultOidStr = AccessController.doPrivileged
             (new GetPropertyAction(DEFAULT_MECH_PROP));
         if (defaultOidStr != null) {
             defOid = GSSUtil.createOid(defaultOidStr);
         }
         DEFAULT_MECH_OID =
             (defOid == null ? GSSUtil.GSS_KRB5_MECH_OID : defOid);
    }

     private ArrayList<PreferencesEntry> preferences =
                         new ArrayList<PreferencesEntry>(5);
     private HashMap<PreferencesEntry, MechanismFactory> factories =
                         new HashMap<PreferencesEntry, MechanismFactory>(5);
     private HashSet<Oid> mechs = new HashSet<Oid>(5);

     final private GSSCaller caller;

     public ProviderList(GSSCaller caller, boolean useNative) {
         this.caller = caller;
         Provider[] provList;
         if (useNative) {
             provList = new Provider[1];
             provList[0] = new SunNativeProvider();
         } else {
             provList = Security.getProviders();
         }

         for (int i = 0; i < provList.length; i++) {
             Provider prov = provList[i];
             try {
                 addProviderAtEnd(prov, null);
             } catch (GSSException ge) {
                 // Move on to the next provider
                 GSSUtil.debug("Error in adding provider " +
                               prov.getName() + ": " + ge);
             }
         } // End of for loop
     }

     /**
      * Determines if the given provider property represents a GSS-API
      * Oid to MechanismFactory mapping.
      * @return true if this is a GSS-API property, false otherwise.
      */
     private boolean isMechFactoryProperty(String prop) {
         return (prop.startsWith(PROV_PROP_PREFIX) ||
                 prop.regionMatches(true, 0, // Try ignoring case
                                    PROV_PROP_PREFIX, 0,
                                    PROV_PROP_PREFIX_LEN));
     }

     private Oid getOidFromMechFactoryProperty(String prop)
         throws GSSException {

         String oidPart = prop.substring(PROV_PROP_PREFIX_LEN);
         return new Oid(oidPart);
     }

     // So the existing code do not have to be changed
     synchronized public MechanismFactory getMechFactory(Oid mechOid)
         throws GSSException {
         if (mechOid == null) mechOid = ProviderList.DEFAULT_MECH_OID;
         return getMechFactory(mechOid, null);
     }

     /**
      * Obtains a MechanismFactory for a given mechanism. If the
      * specified provider is not null, then the impl from the
      * provider is used. Otherwise, the most preferred impl based
      * on the configured preferences is used.
      * @param mechOid the oid of the desired mechanism
      * @return a MechanismFactory for the desired mechanism.
      * @throws GSSException when the specified provider does not
      * support the desired mechanism, or when no provider supports
      * the desired mechanism.
      */
     synchronized public MechanismFactory getMechFactory(Oid mechOid,
                                                         Provider p)
         throws GSSException {

         if (mechOid == null) mechOid = ProviderList.DEFAULT_MECH_OID;

         if (p == null) {
             // Iterate thru all preferences to find right provider
             String className;
             PreferencesEntry entry;

             Iterator<PreferencesEntry> list = preferences.iterator();
             while (list.hasNext()) {
                 entry = list.next();
                 if (entry.impliesMechanism(mechOid)) {
                     MechanismFactory retVal = getMechFactory(entry, mechOid);
                     if (retVal != null) return retVal;
                 }
             } // end of while loop
             throw new GSSExceptionImpl(GSSException.BAD_MECH, mechOid);
         } else {
             // Use the impl from the specified provider; return null if the
             // the mech is unsupported by the specified provider.
             PreferencesEntry entry = new PreferencesEntry(p, mechOid);
             return getMechFactory(entry, mechOid);
         }
     }

     /**
      * Helper routine that uses a preferences entry to obtain an
      * implementation of a MechanismFactory from it.
      * @param e the preferences entry that contains the provider and
      * either a null of an explicit oid that matched the oid of the
      * desired mechanism.
      * @param mechOid the oid of the desired mechanism
      * @throws GSSException If the application explicitly requested
      * this entry's provider to be used for the desired mechanism but
      * some problem is encountered
      */
     private MechanismFactory getMechFactory(PreferencesEntry e, Oid mechOid)
         throws GSSException {
         Provider p = e.getProvider();

         /*
          * See if a MechanismFactory was previously instantiated for
          * this provider and mechanism combination.
          */
         PreferencesEntry searchEntry = new PreferencesEntry(p, mechOid);
         MechanismFactory retVal = factories.get(searchEntry);
         if (retVal == null) {
             /*
              * Apparently not. Now try to instantiate this class from
              * the provider.
              */
             String prop = PROV_PROP_PREFIX + mechOid.toString();
             String className = p.getProperty(prop);
             if (className != null) {
                 retVal = getMechFactoryImpl(p, className, mechOid, caller);
                 factories.put(searchEntry, retVal);
             } else {
                 /*
                  * This provider does not support this mechanism.
                  * If the application explicitly requested that
                  * this provider be used for this mechanism, then
                  * throw an exception
                  */
                 if (e.getOid() != null) {
                     throw new GSSExceptionImpl(GSSException.BAD_MECH,
                          "Provider " + p.getName() +
                          " does not support mechanism " + mechOid);
                 }
             }
         }
         return retVal;
     }

     /**
      * Helper routine to obtain a MechanismFactory implementation
      * from the same class loader as the provider of this
      * implementation.
      * @param p the provider whose classloader must be used for
      * instantiating the desired MechanismFactory
      * @ param className the name of the MechanismFactory class
      * @throws GSSException If some error occurs when trying to
      * instantiate this MechanismFactory.
      */
     private static MechanismFactory getMechFactoryImpl(Provider p,
                                                        String className,
                                                        Oid mechOid,
                                                        GSSCaller caller)
         throws GSSException {

         try {
             Class<?> baseClass = Class.forName(SPI_MECH_FACTORY_TYPE);

             /*
              * Load the implementation class with the same class loader
              * that was used to load the provider.
              * In order to get the class loader of a class, the
              * caller's class loader must be the same as or an ancestor of
              * the class loader being returned. Otherwise, the caller must
              * have "getClassLoader" permission, or a SecurityException
              * will be thrown.
              */

             ClassLoader cl = p.getClass().getClassLoader();
             Class<?> implClass;
             if (cl != null) {
                 implClass = cl.loadClass(className);
             } else {
                 implClass = Class.forName(className);
             }

             if (baseClass.isAssignableFrom(implClass)) {

                 java.lang.reflect.Constructor<?> c =
                                 implClass.getConstructor(GSSCaller.class);
                 MechanismFactory mf = (MechanismFactory) (c.newInstance(caller));

                 if (mf instanceof NativeGSSFactory) {
                     ((NativeGSSFactory) mf).setMech(mechOid);
                 }
                 return mf;
             } else {
                 throw createGSSException(p, className, "is not a " +
                                          SPI_MECH_FACTORY_TYPE, null);
             }
         } catch (ClassNotFoundException e) {
             throw createGSSException(p, className, "cannot be created", e);
         } catch (NoSuchMethodException e) {
             throw createGSSException(p, className, "cannot be created", e);
         } catch (InvocationTargetException e) {
             throw createGSSException(p, className, "cannot be created", e);
         } catch (InstantiationException e) {
             throw createGSSException(p, className, "cannot be created", e);
         } catch (IllegalAccessException e) {
             throw createGSSException(p, className, "cannot be created", e);
         } catch (SecurityException e) {
             throw createGSSException(p, className, "cannot be created", e);
         }
     }

     // Only used by getMechFactoryImpl
     private static GSSException createGSSException(Provider p,
                                                    String className,
                                                    String trailingMsg,
                                                    Exception cause) {
         String errClassInfo = className + " configured by " +
             p.getName() + " for GSS-API Mechanism Factory ";
         return new GSSExceptionImpl(GSSException.BAD_MECH,
                                     errClassInfo + trailingMsg,
                                     cause);
     }

     public Oid[] getMechs() {
         return mechs.toArray(new Oid[] {});
     }

     synchronized public void addProviderAtFront(Provider p, Oid mechOid)
         throws GSSException {

         PreferencesEntry newEntry = new PreferencesEntry(p, mechOid);
         PreferencesEntry oldEntry;
         boolean foundSomeMech;

         Iterator<PreferencesEntry> list = preferences.iterator();
         while (list.hasNext()) {
             oldEntry = list.next();
             if (newEntry.implies(oldEntry))
                 list.remove();
         }

         if (mechOid == null) {
             foundSomeMech = addAllMechsFromProvider(p);
         } else {
             String oidStr = mechOid.toString();
             if (p.getProperty(PROV_PROP_PREFIX + oidStr) == null)
                 throw new GSSExceptionImpl(GSSException.BAD_MECH,
                                            "Provider " + p.getName()
                                            + " does not support "
                                            + oidStr);
             mechs.add(mechOid);
             foundSomeMech = true;
         }

         if (foundSomeMech) {
             preferences.add(0, newEntry);
         }
     }

     synchronized public void addProviderAtEnd(Provider p, Oid mechOid)
         throws GSSException {

         PreferencesEntry newEntry = new PreferencesEntry(p, mechOid);
         PreferencesEntry oldEntry;
         boolean foundSomeMech;

         Iterator<PreferencesEntry> list = preferences.iterator();
         while (list.hasNext()) {
             oldEntry = list.next();
             if (oldEntry.implies(newEntry))
                 return;
         }

         // System.out.println("addProviderAtEnd: No it is not redundant");

         if (mechOid == null)
             foundSomeMech = addAllMechsFromProvider(p);
         else {
             String oidStr = mechOid.toString();
             if (p.getProperty(PROV_PROP_PREFIX + oidStr) == null)
                 throw new GSSExceptionImpl(GSSException.BAD_MECH,
                                        "Provider " + p.getName()
                                        + " does not support "
                                        + oidStr);
             mechs.add(mechOid);
             foundSomeMech = true;
         }

         if (foundSomeMech) {
             preferences.add(newEntry);
         }
     }

     /**
      * Helper routine to go through all properties contined in a
      * provider and add its mechanisms to the list of supported
      * mechanisms. If no default mechanism has been assinged so far,
      * it sets the default MechanismFactory and Oid as well.
      * @param p the provider to query
      * @return true if there is at least one mechanism that this
      * provider contributed, false otherwise
      */
     private boolean addAllMechsFromProvider(Provider p) {

         String prop;
         boolean retVal = false;

         // Get all props for this provider
         Enumeration<Object> props = p.keys();

         // See if there are any GSS prop's
         while (props.hasMoreElements()) {
             prop = (String) props.nextElement();
             if (isMechFactoryProperty(prop)) {
                 // Ok! This is a GSS provider!
                 try {
                     Oid mechOid = getOidFromMechFactoryProperty(prop);
                     mechs.add(mechOid);
                     retVal = true;
                 } catch (GSSException e) {
                     // Skip to next property
                     GSSUtil.debug("Ignore the invalid property " +
                                   prop + " from provider " + p.getName());
                 }
             } // Processed GSS property
         } // while loop

         return retVal;

     }

     /**
      * Stores a provider and a mechanism oid indicating that the
      * provider should be used for the mechanism. If the mechanism
      * Oid is null, then it indicates that this preference holds for
      * any mechanism.<p>
      *
      * The ProviderList maintains an ordered list of
      * PreferencesEntry's and iterates thru them as it tries to
      * instantiate MechanismFactory's.
      */
     private static final class PreferencesEntry {
         private Provider p;
         private Oid oid;
         PreferencesEntry(Provider p, Oid oid) {
             this.p = p;
             this.oid = oid;
         }

         public boolean equals(Object other) {
             if (this == other) {
                 return true;
             }

             if (!(other instanceof PreferencesEntry)) {
                 return false;
             }

             PreferencesEntry that = (PreferencesEntry)other;
             if (this.p.getName().equals(that.p.getName())) {
                 if (this.oid != null && that.oid != null) {
                     return this.oid.equals(that.oid);
                 } else {
                     return (this.oid == null && that.oid == null);
                 }
             }

             return false;
         }

         public int hashCode() {
             int result = 17;

             result = 37 * result + p.getName().hashCode();
             if (oid != null) {
                 result = 37 * result + oid.hashCode();
             }

             return result;
         }

         /**
          * Determines if a preference implies another. A preference
          * implies another if the latter is subsumed by the
          * former. e.g., <Provider1, null> implies <Provider1, OidX>
          * because the null in the former indicates that it should
          * be used for all mechanisms.
          */
         boolean implies(Object other) {

             if (other instanceof PreferencesEntry) {
                 PreferencesEntry temp = (PreferencesEntry) other;
                 return (equals(temp) ||
                         p.getName().equals(temp.p.getName()) &&
                         oid == null);
             } else {
                 return false;
             }
         }

         Provider getProvider() {
             return p;
         }

         Oid getOid() {
             return oid;
         }

         /**
          * Determines if this entry is applicable to the desired
          * mechanism. The entry is applicable to the desired mech if
          * it contains the same oid or if it contains a null oid
          * indicating that it is applicable to all mechs.
          * @param mechOid the desired mechanism
          * @return true if the provider in this entry should be
          * queried for this mechanism.
          */
         boolean impliesMechanism(Oid oid) {
             return (this.oid == null || this.oid.equals(oid));
         }

         // For debugging
         public String toString() {
             StringBuffer buf = new StringBuffer("<");
             buf.append(p.getName());
             buf.append(", ");
             buf.append(oid);
             buf.append(">");
             return buf.toString();
         }
     }
 }
	/*
	* Copyright (c) 2000, 2009, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package sun.security.jgss;

	import java.lang.reflect.InvocationTargetException;
	import org.ietf.jgss.*;
	import java.security.AccessController;
	import java.security.Provider;
	import java.security.Security;
	import java.util.ArrayList;
	import java.util.HashSet;
	import java.util.HashMap;
	import java.util.Enumeration;
	import java.util.Iterator;
	import sun.security.jgss.spi.*;
	import sun.security.jgss.wrapper.NativeGSSFactory;
	import sun.security.jgss.wrapper.SunNativeProvider;
	import sun.security.action.GetPropertyAction;

	/**
	* This class stores the list of providers that this
	* GSS-Implementation is configured to use. The GSSManagerImpl class
	* queries this class whenever it needs a mechanism's factory.<p>
	*
	* This class stores an ordered list of pairs of the form
	* <provider, oid>. When it attempts to instantiate a mechanism
	* defined by oid o, it steps through the list looking for an entry
	* with oid=o, or with oid=null. (An entry with oid=null matches all
	* mechanisms.) When it finds such an entry, the corresponding
	* provider is approached for the mechanism's factory class.
	* At instantiation time this list in initialized to contain those
	* system wide providers that contain a property of the form
	* "GssApiMechanism.x.y.z..." where "x.y.z..." is a numeric object
	* identifier with numbers x, y, z, etc. Such a property is defined
	* to map to that provider's implementation of the MechanismFactory
	* interface for the mechanism x.y.z...
	* As and when a MechanismFactory is instantiated, it is
	* cached for future use. <p>
	*
	* An application can cause more providers to be added by means of
	* the addProviderAtFront and addProviderAtEnd methods on
	* GSSManager which get delegated to this class. The
	* addProviderAtFront method can also cause a change in the ordering
	* of the providers without adding any new providers, by causing a
	* provider to move up in a list. The method addProviderAtEnd can
	* only add providers at the end of the list if they are not already
	* in the list. The rationale is that an application will call
	* addProviderAtFront when it wants a provider to be used in
	* preference over the default ones. And it will call
	* addProviderAtEnd when it wants a provider to be used in case
	* the system ones don't suffice.<p>
	*
	* If a mechanism's factory is being obtained from a provider as a
	* result of encountering a entryof the form <provider, oid> where
	* oid is non-null, then the assumption is that the application added
	* this entry and it wants this mechanism to be obtained from this
	* provider. Thus is the provider does not actually contain the
	* requested mechanism, an exception will be thrown. However, if the
	* entry were of the form <provider, null>, then it is viewed more
	* liberally and is simply skipped over if the provider does not claim to
	* support the requested mechanism.
	*/

	public final class ProviderList {

	private static final String PROV_PROP_PREFIX = "GssApiMechanism.";
	private static final int PROV_PROP_PREFIX_LEN =
	PROV_PROP_PREFIX.length();

	private static final String SPI_MECH_FACTORY_TYPE
	= "sun.security.jgss.spi.MechanismFactory";

	// Undocumented property?
	private static final String DEFAULT_MECH_PROP =
	"sun.security.jgss.mechanism";

	public static final Oid DEFAULT_MECH_OID;

	static {
	/*
	* Set the default mechanism. Kerberos v5 is the default
	* mechanism unless it is overridden by a system property.
	* with a valid OID value
	*/
	Oid defOid = null;
	String defaultOidStr = AccessController.doPrivileged
	(new GetPropertyAction(DEFAULT_MECH_PROP));
	if (defaultOidStr != null) {
	defOid = GSSUtil.createOid(defaultOidStr);
	}
	DEFAULT_MECH_OID =
	(defOid == null ? GSSUtil.GSS_KRB5_MECH_OID : defOid);
	}

	private ArrayList<PreferencesEntry> preferences =
	new ArrayList<PreferencesEntry>(5);
	private HashMap<PreferencesEntry, MechanismFactory> factories =
	new HashMap<PreferencesEntry, MechanismFactory>(5);
	private HashSet<Oid> mechs = new HashSet<Oid>(5);

	final private GSSCaller caller;

	public ProviderList(GSSCaller caller, boolean useNative) {
	this.caller = caller;
	Provider[] provList;
	if (useNative) {
	provList = new Provider[1];
	provList[0] = new SunNativeProvider();
	} else {
	provList = Security.getProviders();
	}

	for (int i = 0; i < provList.length; i++) {
	Provider prov = provList[i];
	try {
	addProviderAtEnd(prov, null);
	} catch (GSSException ge) {
	// Move on to the next provider
	GSSUtil.debug("Error in adding provider " +
	prov.getName() + ": " + ge);
	}
	} // End of for loop
	}

	/**
	* Determines if the given provider property represents a GSS-API
	* Oid to MechanismFactory mapping.
	* @return true if this is a GSS-API property, false otherwise.
	*/
	private boolean isMechFactoryProperty(String prop) {
	return (prop.startsWith(PROV_PROP_PREFIX) \|\|
	prop.regionMatches(true, 0, // Try ignoring case
	PROV_PROP_PREFIX, 0,
	PROV_PROP_PREFIX_LEN));
	}

	private Oid getOidFromMechFactoryProperty(String prop)
	throws GSSException {

	String oidPart = prop.substring(PROV_PROP_PREFIX_LEN);
	return new Oid(oidPart);
	}

	// So the existing code do not have to be changed
	synchronized public MechanismFactory getMechFactory(Oid mechOid)
	throws GSSException {
	if (mechOid == null) mechOid = ProviderList.DEFAULT_MECH_OID;
	return getMechFactory(mechOid, null);
	}

	/**
	* Obtains a MechanismFactory for a given mechanism. If the
	* specified provider is not null, then the impl from the
	* provider is used. Otherwise, the most preferred impl based
	* on the configured preferences is used.
	* @param mechOid the oid of the desired mechanism
	* @return a MechanismFactory for the desired mechanism.
	* @throws GSSException when the specified provider does not
	* support the desired mechanism, or when no provider supports
	* the desired mechanism.
	*/
	synchronized public MechanismFactory getMechFactory(Oid mechOid,
	Provider p)
	throws GSSException {

	if (mechOid == null) mechOid = ProviderList.DEFAULT_MECH_OID;

	if (p == null) {
	// Iterate thru all preferences to find right provider
	String className;
	PreferencesEntry entry;

	Iterator<PreferencesEntry> list = preferences.iterator();
	while (list.hasNext()) {
	entry = list.next();
	if (entry.impliesMechanism(mechOid)) {
	MechanismFactory retVal = getMechFactory(entry, mechOid);
	if (retVal != null) return retVal;
	}
	} // end of while loop
	throw new GSSExceptionImpl(GSSException.BAD_MECH, mechOid);
	} else {
	// Use the impl from the specified provider; return null if the
	// the mech is unsupported by the specified provider.
	PreferencesEntry entry = new PreferencesEntry(p, mechOid);
	return getMechFactory(entry, mechOid);
	}
	}

	/**
	* Helper routine that uses a preferences entry to obtain an
	* implementation of a MechanismFactory from it.
	* @param e the preferences entry that contains the provider and
	* either a null of an explicit oid that matched the oid of the
	* desired mechanism.
	* @param mechOid the oid of the desired mechanism
	* @throws GSSException If the application explicitly requested
	* this entry's provider to be used for the desired mechanism but
	* some problem is encountered
	*/
	private MechanismFactory getMechFactory(PreferencesEntry e, Oid mechOid)
	throws GSSException {
	Provider p = e.getProvider();

	/*
	* See if a MechanismFactory was previously instantiated for
	* this provider and mechanism combination.
	*/
	PreferencesEntry searchEntry = new PreferencesEntry(p, mechOid);
	MechanismFactory retVal = factories.get(searchEntry);
	if (retVal == null) {
	/*
	* Apparently not. Now try to instantiate this class from
	* the provider.
	*/
	String prop = PROV_PROP_PREFIX + mechOid.toString();
	String className = p.getProperty(prop);
	if (className != null) {
	retVal = getMechFactoryImpl(p, className, mechOid, caller);
	factories.put(searchEntry, retVal);
	} else {
	/*
	* This provider does not support this mechanism.
	* If the application explicitly requested that
	* this provider be used for this mechanism, then
	* throw an exception
	*/
	if (e.getOid() != null) {
	throw new GSSExceptionImpl(GSSException.BAD_MECH,
	"Provider " + p.getName() +
	" does not support mechanism " + mechOid);
	}
	}
	}
	return retVal;
	}

	/**
	* Helper routine to obtain a MechanismFactory implementation
	* from the same class loader as the provider of this
	* implementation.
	* @param p the provider whose classloader must be used for
	* instantiating the desired MechanismFactory
	* @ param className the name of the MechanismFactory class
	* @throws GSSException If some error occurs when trying to
	* instantiate this MechanismFactory.
	*/
	private static MechanismFactory getMechFactoryImpl(Provider p,
	String className,
	Oid mechOid,
	GSSCaller caller)
	throws GSSException {

	try {
	Class<?> baseClass = Class.forName(SPI_MECH_FACTORY_TYPE);

	/*
	* Load the implementation class with the same class loader
	* that was used to load the provider.
	* In order to get the class loader of a class, the
	* caller's class loader must be the same as or an ancestor of
	* the class loader being returned. Otherwise, the caller must
	* have "getClassLoader" permission, or a SecurityException
	* will be thrown.
	*/

	ClassLoader cl = p.getClass().getClassLoader();
	Class<?> implClass;
	if (cl != null) {
	implClass = cl.loadClass(className);
	} else {
	implClass = Class.forName(className);
	}

	if (baseClass.isAssignableFrom(implClass)) {

	java.lang.reflect.Constructor<?> c =
	implClass.getConstructor(GSSCaller.class);
	MechanismFactory mf = (MechanismFactory) (c.newInstance(caller));

	if (mf instanceof NativeGSSFactory) {
	((NativeGSSFactory) mf).setMech(mechOid);
	}
	return mf;
	} else {
	throw createGSSException(p, className, "is not a " +
	SPI_MECH_FACTORY_TYPE, null);
	}
	} catch (ClassNotFoundException e) {
	throw createGSSException(p, className, "cannot be created", e);
	} catch (NoSuchMethodException e) {
	throw createGSSException(p, className, "cannot be created", e);
	} catch (InvocationTargetException e) {
	throw createGSSException(p, className, "cannot be created", e);
	} catch (InstantiationException e) {
	throw createGSSException(p, className, "cannot be created", e);
	} catch (IllegalAccessException e) {
	throw createGSSException(p, className, "cannot be created", e);
	} catch (SecurityException e) {
	throw createGSSException(p, className, "cannot be created", e);
	}
	}

	// Only used by getMechFactoryImpl
	private static GSSException createGSSException(Provider p,
	String className,
	String trailingMsg,
	Exception cause) {
	String errClassInfo = className + " configured by " +
	p.getName() + " for GSS-API Mechanism Factory ";
	return new GSSExceptionImpl(GSSException.BAD_MECH,
	errClassInfo + trailingMsg,
	cause);
	}

	public Oid[] getMechs() {
	return mechs.toArray(new Oid[] {});
	}

	synchronized public void addProviderAtFront(Provider p, Oid mechOid)
	throws GSSException {

	PreferencesEntry newEntry = new PreferencesEntry(p, mechOid);
	PreferencesEntry oldEntry;
	boolean foundSomeMech;

	Iterator<PreferencesEntry> list = preferences.iterator();
	while (list.hasNext()) {
	oldEntry = list.next();
	if (newEntry.implies(oldEntry))
	list.remove();
	}

	if (mechOid == null) {
	foundSomeMech = addAllMechsFromProvider(p);
	} else {
	String oidStr = mechOid.toString();
	if (p.getProperty(PROV_PROP_PREFIX + oidStr) == null)
	throw new GSSExceptionImpl(GSSException.BAD_MECH,
	"Provider " + p.getName()
	+ " does not support "
	+ oidStr);
	mechs.add(mechOid);
	foundSomeMech = true;
	}

	if (foundSomeMech) {
	preferences.add(0, newEntry);
	}
	}

	synchronized public void addProviderAtEnd(Provider p, Oid mechOid)
	throws GSSException {

	PreferencesEntry newEntry = new PreferencesEntry(p, mechOid);
	PreferencesEntry oldEntry;
	boolean foundSomeMech;

	Iterator<PreferencesEntry> list = preferences.iterator();
	while (list.hasNext()) {
	oldEntry = list.next();
	if (oldEntry.implies(newEntry))
	return;
	}

	// System.out.println("addProviderAtEnd: No it is not redundant");

	if (mechOid == null)
	foundSomeMech = addAllMechsFromProvider(p);
	else {
	String oidStr = mechOid.toString();
	if (p.getProperty(PROV_PROP_PREFIX + oidStr) == null)
	throw new GSSExceptionImpl(GSSException.BAD_MECH,
	"Provider " + p.getName()
	+ " does not support "
	+ oidStr);
	mechs.add(mechOid);
	foundSomeMech = true;
	}

	if (foundSomeMech) {
	preferences.add(newEntry);
	}
	}

	/**
	* Helper routine to go through all properties contined in a
	* provider and add its mechanisms to the list of supported
	* mechanisms. If no default mechanism has been assinged so far,
	* it sets the default MechanismFactory and Oid as well.
	* @param p the provider to query
	* @return true if there is at least one mechanism that this
	* provider contributed, false otherwise
	*/
	private boolean addAllMechsFromProvider(Provider p) {

	String prop;
	boolean retVal = false;

	// Get all props for this provider
	Enumeration<Object> props = p.keys();

	// See if there are any GSS prop's
	while (props.hasMoreElements()) {
	prop = (String) props.nextElement();
	if (isMechFactoryProperty(prop)) {
	// Ok! This is a GSS provider!
	try {
	Oid mechOid = getOidFromMechFactoryProperty(prop);
	mechs.add(mechOid);
	retVal = true;
	} catch (GSSException e) {
	// Skip to next property
	GSSUtil.debug("Ignore the invalid property " +
	prop + " from provider " + p.getName());
	}
	} // Processed GSS property
	} // while loop

	return retVal;

	}

	/**
	* Stores a provider and a mechanism oid indicating that the
	* provider should be used for the mechanism. If the mechanism
	* Oid is null, then it indicates that this preference holds for
	* any mechanism.<p>
	*
	* The ProviderList maintains an ordered list of
	* PreferencesEntry's and iterates thru them as it tries to
	* instantiate MechanismFactory's.
	*/
	private static final class PreferencesEntry {
	private Provider p;
	private Oid oid;
	PreferencesEntry(Provider p, Oid oid) {
	this.p = p;
	this.oid = oid;
	}

	public boolean equals(Object other) {
	if (this == other) {
	return true;
	}

	if (!(other instanceof PreferencesEntry)) {
	return false;
	}

	PreferencesEntry that = (PreferencesEntry)other;
	if (this.p.getName().equals(that.p.getName())) {
	if (this.oid != null && that.oid != null) {
	return this.oid.equals(that.oid);
	} else {
	return (this.oid == null && that.oid == null);
	}
	}

	return false;
	}

	public int hashCode() {
	int result = 17;

	result = 37 * result + p.getName().hashCode();
	if (oid != null) {
	result = 37 * result + oid.hashCode();
	}

	return result;
	}

	/**
	* Determines if a preference implies another. A preference
	* implies another if the latter is subsumed by the
	* former. e.g., <Provider1, null> implies <Provider1, OidX>
	* because the null in the former indicates that it should
	* be used for all mechanisms.
	*/
	boolean implies(Object other) {

	if (other instanceof PreferencesEntry) {
	PreferencesEntry temp = (PreferencesEntry) other;
	return (equals(temp) \|\|
	p.getName().equals(temp.p.getName()) &&
	oid == null);
	} else {
	return false;
	}
	}

	Provider getProvider() {
	return p;
	}

	Oid getOid() {
	return oid;
	}

	/**
	* Determines if this entry is applicable to the desired
	* mechanism. The entry is applicable to the desired mech if
	* it contains the same oid or if it contains a null oid
	* indicating that it is applicable to all mechs.
	* @param mechOid the desired mechanism
	* @return true if the provider in this entry should be
	* queried for this mechanism.
	*/
	boolean impliesMechanism(Oid oid) {
	return (this.oid == null \|\| this.oid.equals(oid));
	}

	// For debugging
	public String toString() {
	StringBuffer buf = new StringBuffer("<");
	buf.append(p.getName());
	buf.append(", ");
	buf.append(oid);
	buf.append(">");
	return buf.toString();
	}
	}
	}