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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * particular file as subject to the "Classpath" exception as provided

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 * 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,

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 *

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package javax.naming.ldap;

import javax.naming.NamingException;

import javax.naming.Context;

import java.util.Hashtable;

import com.sun.naming.internal.FactoryEnumeration;

import com.sun.naming.internal.ResourceManager;

/**

  * This abstract class represents a factory for creating LDAPv3 controls.

  * LDAPv3 controls are defined in

  * <A HREF="http://www.ietf.org/rfc/rfc2251.txt">RFC 2251</A>.

  *<p>

  * When a service provider receives a response control, it uses control

  * factories to return the specific/appropriate control class implementation.

  *

  * @author Rosanna Lee

  * @author Scott Seligman

  * @author Vincent Ryan

  *

  * @see Control

  * @since 1.3

  */

public abstract class ControlFactory {

    /**

     * Creates a new instance of a control factory.

     */

    protected ControlFactory() {

    }

    /**

      * Creates a control using this control factory.

      *<p>

      * The factory is used by the service provider to return controls

      * that it reads from the LDAP protocol as specialized control classes.

      * Without this mechanism, the provider would be returning

      * controls that only contained data in BER encoded format.

      *<p>

      * Typically, {@code ctl} is a "basic" control containing

      * BER encoded data. The factory is used to create a specialized

      * control implementation, usually by decoding the BER encoded data,

      * that provides methods to access that data in a type-safe and friendly

      * manner.

      * <p>

      * For example, a factory might use the BER encoded data in

      * basic control and return an instance of a VirtualListReplyControl.

      *<p>

      * If this factory cannot create a control using the argument supplied,

      * it should return null.

      * A factory should only throw an exception if it is sure that

      * it is the only intended factory and that no other control factories

      * should be tried. This might happen, for example, if the BER data

      * in the control does not match what is expected of a control with

      * the given OID. Since this method throws {@code NamingException},

      * any other internally generated exception that should be propagated

      * must be wrapped inside a {@code NamingException}.

      *

      * @param ctl A non-null control.

      *

      * @return A possibly null Control.

      * @exception NamingException If {@code ctl} contains invalid data that prevents it

      * from being used to create a control. A factory should only throw

      * an exception if it knows how to produce the control (identified by the OID)

      * but is unable to because of, for example invalid BER data.

      */

    public abstract Control getControlInstance(Control ctl) throws NamingException;

    /**

      * Creates a control using known control factories.

      * <p>

      * The following rule is used to create the control:

      *<ul>

      * <li> Use the control factories specified in

      *    the {@code LdapContext.CONTROL_FACTORIES} property of the

      *    environment, and of the provider resource file associated with

      *    {@code ctx}, in that order.

      *    The value of this property is a colon-separated list of factory

      *    class names that are tried in order, and the first one that succeeds

      *    in creating the control is the one used.

      *    If none of the factories can be loaded,

      *    return {@code ctl}.

      *    If an exception is encountered while creating the control, the

      *    exception is passed up to the caller.

      *</ul>

      * <p>

      * Note that a control factory

      * must be public and must have a public constructor that accepts no arguments.

      *

      * @param ctl The non-null control object containing the OID and BER data.

      * @param ctx The possibly null context in which the control is being created.

      * If null, no such information is available.

      * @param env The possibly null environment of the context. This is used

      * to find the value of the {@code LdapContext.CONTROL_FACTORIES} property.

      * @return A control object created using {@code ctl}; or

      *         {@code ctl} if a control object cannot be created using

      *         the algorithm described above.

      * @exception NamingException if a naming exception was encountered

      *         while attempting to create the control object.

      *         If one of the factories accessed throws an

      *         exception, it is propagated up to the caller.

      * If an error was encountered while loading

      * and instantiating the factory and object classes, the exception

      * is wrapped inside a {@code NamingException} and then rethrown.

      */

    public static Control getControlInstance(Control ctl, Context ctx,

                                             Hashtable<?,?> env)

        throws NamingException {

        // Get object factories list from environment properties or

        // provider resource file.

        FactoryEnumeration factories = ResourceManager.getFactories(

            LdapContext.CONTROL_FACTORIES, env, ctx);

        if (factories == null) {

            return ctl;

        }

        // Try each factory until one succeeds

        Control answer = null;

        ControlFactory factory;

        while (answer == null && factories.hasMore()) {

            factory = (ControlFactory)factories.next();

            answer = factory.getControlInstance(ctl);

        }

        return (answer != null)? answer : ctl;

    }

}