* A service provider provides * a subclass of {@code ReferralException} by providing implementations * for {@code getReferralInfo()} and {@code getReferralContext()} (and appropriate * constructors and/or corresponding "set" methods). *
* The following code sample shows how {@code ReferralException} can be used. *
{@code
* while (true) {
* try {
* bindings = ctx.listBindings(name);
* while (bindings.hasMore()) {
* b = bindings.next();
* ...
* }
* break;
* } catch (ReferralException e) {
* ctx = e.getReferralContext();
* }
* }
* }* {@code ReferralException} is an abstract class. Concrete implementations * determine its synchronization and serialization properties. *
* An environment parameter passed to the {@code getReferralContext()} * method is owned by the caller. * The service provider will not modify the object or keep a reference to it, * but may keep a reference to a clone of it. * * @author Rosanna Lee * @author Scott Seligman * * @since 1.3 * */ public abstract class ReferralException extends NamingException { /** * Constructs a new instance of ReferralException using the * explanation supplied. All other fields are set to null. * * @param explanation Additional detail about this exception. Can be null. * @see java.lang.Throwable#getMessage */ protected ReferralException(String explanation) { super(explanation); } /** * Constructs a new instance of ReferralException. * All fields are set to null. */ protected ReferralException() { super(); } /** * Retrieves information (such as URLs) related to this referral. * The program may examine or display this information * to the user to determine whether to continue with the referral, * or to determine additional information needs to be supplied in order * to continue with the referral. * * @return Non-null referral information related to this referral. */ public abstract Object getReferralInfo(); /** * Retrieves the context at which to continue the method. * Regardless of whether a referral is encountered directly during a * context operation, or indirectly, for example, during a search * enumeration, the referral exception should provide a context * at which to continue the operation. The referral context is * created using the environment properties of the context * that threw the ReferralException. * *
* To continue the operation, the client program should re-invoke * the method using the same arguments as the original invocation. * * @return The non-null context at which to continue the method. * @exception NamingException If a naming exception was encountered. * Call either {@code retryReferral()} or {@code skipReferral()} * to continue processing referrals. */ public abstract Context getReferralContext() throws NamingException; /** * Retrieves the context at which to continue the method using * environment properties. * Regardless of whether a referral is encountered directly during a * context operation, or indirectly, for example, during a search * enumeration, the referral exception should provide a context * at which to continue the operation. *
* The referral context is created using {@code env} as its environment * properties. * This method should be used instead of the no-arg overloaded form * when the caller needs to use different environment properties for * the referral context. It might need to do this, for example, when * it needs to supply different authentication information to the referred * server in order to create the referral context. *
* To continue the operation, the client program should re-invoke * the method using the same arguments as the original invocation. * * @param env The possibly null environment to use when retrieving the * referral context. If null, no environment properties will be used. * * @return The non-null context at which to continue the method. * @exception NamingException If a naming exception was encountered. * Call either {@code retryReferral()} or {@code skipReferral()} * to continue processing referrals. */ public abstract Context getReferralContext(Hashtable env) throws NamingException; /** * Discards the referral about to be processed. * A call to this method should be followed by a call to * {@code getReferralContext} to allow the processing of * other referrals to continue. * The following code fragment shows a typical usage pattern. *
{@code
* } catch (ReferralException e) {
* if (!shallIFollow(e.getReferralInfo())) {
* if (!e.skipReferral()) {
* return;
* }
* }
* ctx = e.getReferralContext();
* }
* }{@code
* } catch (ReferralException e) {
* while (true) {
* try {
* ctx = e.getReferralContext(env);
* break;
* } catch (NamingException ne) {
* if (! shallIRetry()) {
* return;
* }
* // modify environment properties (env), if necessary
* e.retryReferral();
* }
* }
* }
* }