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* accompanied this code).
*
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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.
* In cases where the factory is in a named module then it must be in a
* package which is exported by that module to the {@code java.naming}
* module.
*
* @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,
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