net.jini.discovery

Interface LookupDiscoveryRegistration

public interface LookupDiscoveryRegistration

When a client requests a registration with a lookup discovery service, an instance of this interface is returned. It is through this interface that the client manages the parameters reflected in its registration with the lookup discovery service.

This interface is not a remote interface; each implementation of the lookup discovery service exports proxy objects that implement this interface local to the client, using an implementation-specific protocol to communicate with the actual remote server. The proxy methods obey normal RMI remote interface semantics except where explicitly noted. Two proxy objects are equal if they are proxies for the same registration created by the same lookup discovery service.

If a client's registration with the lookup discovery service has expired or been cancelled, then any invocation of a remote method defined in this interface will result in a java.rmi.NoSuchObjectException.

Each remote method of this interface may throw a RemoteException. Typically, this exception occurs when there is a communication failure between the client's registration object and the lookup discovery service. Whenever this exception occurs as a result of the invocation of one of these methods, the method may or may not have completed its processing successfully.

Author:

Sun Microsystems, Inc.

See Also:

ServiceRegistrar, LookupDiscoveryService

Method Summary

Modifier and Type	Method and Description
void	addGroups(String[] groups) Adds a set of group names to the managed set of groups associated with this registration.
void	addLocators(LookupLocator[] locators) Adds a set of LookupLocator objects to the managed set of locators associated with this registration.
void	discard(ServiceRegistrar registrar) Informs the lookup discovery service of the existence of an unavailable lookup service and requests that the lookup discovery service discard the unavailable lookup service.
EventRegistration	getEventRegistration() Returns an EventRegistration object that encapsulates the information needed by the client to identify a notification sent by the lookup discovery service to the registration's listener.
String[]	getGroups() Returns an array consisting of the names of the groups whose members are lookup services the lookup discovery service will attempt to discover for this registration.
Lease	getLease() Returns the Lease object that controls a client's registration with the lookup discovery service.
LookupLocator[]	getLocators() Returns an array consisting of the LookupLocator objects corresponding to specific lookup services the lookup discovery service will attempt to discover for this registration.
ServiceRegistrar[]	getRegistrars() Returns an array consisting of instances of the ServiceRegistrar interface.
void	removeGroups(String[] groups) Deletes a set of group names from this registration's managed set of groups.
void	removeLocators(LookupLocator[] locators) Deletes a set of of LookupLocator objects from this registration's managed set of locators.
void	setGroups(String[] groups) Replaces all of the group names in this registration's managed set of groups with new set of names.
void	setLocators(LookupLocator[] locators) Replaces all of the locators in this registration's managed set of locators with a new set of LookupLocator objects.

Method Detail

getEventRegistration

EventRegistration getEventRegistration()

Returns an EventRegistration object that encapsulates the information needed by the client to identify a notification sent by the lookup discovery service to the registration's listener. This method is not remote and takes no arguments.

Returns:

the EventRegistration for this registration.

getLease

Lease getLease()

Returns the Lease object that controls a client's registration with the lookup discovery service. It is through the object returned by this method that the client can request the renewal or cancellation of the registration with the lookup discovery service. This method is not remote and takes no arguments.

Note that the object returned by the getEventRegistration method also provides a getLease method. That method and this method both return the same Lease object. This method is provided as a convenience to avoid the indirection associated with the getLease method on the EventRegistration object, as well as to avoid the overhead of making two method calls when retrieving the lease.

Returns:

the Lease on this registration.

getRegistrars

ServiceRegistrar[] getRegistrars()
                          throws LookupUnmarshalException,
                                 RemoteException

Returns an array consisting of instances of the ServiceRegistrar interface. Each element in the returned set is a proxy to one of lookup service(s) that have already been discovered for this registration. The contents of the returned set make up the 'remote state' of this registration's currently discovered lookup service(s). This method returns a new array on each invocation.

This method can be used to maintain synchronization between the set of discovered lookup services making up a registration's local state on the client and the registration's corresponding remote state maintained by the lookup discovery service. The local state can become un-synchronized with the remote state when a gap occurs in the events received by the registration's listener.

According to the event semantics, if there is no gap between two sequence numbers, no events have been missed and the states remain synchronized; if there is a gap, events may or may not have been missed. Thus, upon finding gaps in the sequence of events, the client can invoke this method and use the returned information to synchronize the local state with the remote state.

This method requests that the lookup discovery service return the set of proxies to the lookup services currently discovered for the the particular registration object on which this method is invoked. When the lookup discovery service receives such a request, it sends the requested set of proxies as a set of marshalled instances of the ServiceRegistrar interface. Thus, in order to construct the return set, this method attempts to unmarshal each element of the set received from the lookup discovery service. Should a failure occur while attempting to unmarshal any of the elements of the received set of marshalled proxy objects, this method will throw an exception of type LookupUnmarshalException.

When a LookupUnmarshalException is thrown by this method, the contents of the exception provides the client with the following useful information: (1) the knowledge that a problem has occurred while unmarshalling at least one of the elements making up the remote state of this registration's discovered lookup service(s), (2) the set consisting of the proxy objects that were successfully unmarshalled by this method, (3) the set consisting of the marshalled proxy objects that could not be unmarshalled by this method, and (4) the set of exceptions corresponding to each failed attempt at unmarshalling.

Typically, the type of exception that occurs when attempting to unmarshal an element of the set of marshalled proxies is either an IOException or a ClassNotFoundException. A ClassNotFoundException occurs whenever a remote field of the marshalled proxy cannot be retrieved (usually because the codebase of one of the field's classes or interfaces is currently 'down'). To address this situation, the client may wish to proceed with its processing using the successfully unmarshalled proxies; and attempt to unmarshal the unavailable proxies (or re-invoke this method) at some later time.

Note that if this method returns successfully without throwing a LookupUnmarshalException, the client is guaranteed that all marshalled proxies returned to this method by the lookup discovery service have been successfully unmarshalled; and the client then has a snapshot - relative to the point in time when this method is invoked - of the remote state of the lookup service(s) discovered for this registration.

Returns:

an array of ServiceRegistrar objects.

Throws:

LookupUnmarshalException - this exception is thrown when failure occurs while attempting to unmarshal one or more of the marshalled instances of ServiceRegistrar received from the lookup discovery service.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service.

getGroups

String[] getGroups()
            throws RemoteException

Returns an array consisting of the names of the groups whose members are lookup services the lookup discovery service will attempt to discover for this registration. This set of group names is referred to as the registration's 'managed set of groups'.

If the registration's managed set of groups is currently empty, this method will return the empty array. If the lookup discovery service has no managed set of groups associated with this registration, this method will return null.

Returns:

a String array containing the elements of the managed set of groups for the registration.

Throws:

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service.

See Also:

setGroups(java.lang.String[])

getLocators

LookupLocator[] getLocators()
                     throws RemoteException

Returns an array consisting of the LookupLocator objects corresponding to specific lookup services the lookup discovery service will attempt to discover for this registration. This set of locators is referred to as the registration's 'managed set of locators'.

If the registration's managed set of locators is currently empty, this method will return the empty array. If the lookup discovery service has no managed set of locators associated with this registration, this method will return null.

Returns:

array consisting of net.jini.core.discovery.LookupLocator objects corresponding to the elements of the managed set of locators for the registration.

Throws:

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service.

See Also:

setLocators(net.jini.core.discovery.LookupLocator[])

addGroups

void addGroups(String[] groups)
        throws RemoteException

Adds a set of group names to the managed set of groups associated with this registration.

Parameters:

groups - a String array, none of whose elements may be null, consisting of the group names with which to augment this registration's managed set of groups.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored. If any element of this parameter duplicates any element of the registration's current managed set of groups, the duplicate will be ignored.

If the empty set (equivalent to net.jini.discovery.LookupDiscovery.NO_GROUPS) is input, then this registration's managed set of groups will not change.

If null (equivalent to net.jini.discovery.LookupDiscovery.ALL_GROUPS) is input, this method will throw a NullPointerException.

Throws:

UnsupportedOperationException - this exception occurs when the lookup discovery service has no managed set of groups associated with this registration.

NullPointerException - this exception occurs when either null (net.jini.discovery.LookupDiscovery.ALL_GROUPS) is input to the groups parameter, or one or more of the elements of the groups parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of groups may or may not have been successfully augmented.

See Also:

removeGroups(java.lang.String[])

setGroups

void setGroups(String[] groups)
        throws RemoteException

Replaces all of the group names in this registration's managed set of groups with new set of names.

Once a new group name has been placed in the managed set, if there are lookup services belonging to that group that have already been discovered, no event will be sent to this registration's listener for those particular lookup services. Attempts to discover all as yet undiscovered lookup services belonging to that group will continue to be made for this registration.

After an invocation of this method results in the removal (due to replacement) of one or more group names from the registration's managed set of groups, attempts to discover any lookup service that meets all of the following criteria will cease to be made for this registration: the lookup service is a member of one or more of the removed group(s), but that lookup service is neither a member of any group in the resulting managed set of groups, nor does that lookup service correspond to any element in the registration's managed set of locators.

Parameters:

groups - a String array, none of whose elements may be null, consisting of the group names with which to replace the names in this registration's managed set of groups.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored.

If the empty set (equivalent to net.jini.discovery.LookupDiscovery.NO_GROUPS) is input, then group discovery for this registration will cease.

If null (equivalent to net.jini.discovery.LookupDiscovery.ALL_GROUPS) is input, the lookup discovery service will attempt to discover all as yet undiscovered lookup services located within its multicast radius and, upon discovery of any such lookup service, will send to this registration's listener an event signaling that discovery.

Throws:

NullPointerException - this exception occurs when one or more of the elements of the groups parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of groups may or may not have been successfully replaced.

See Also:

getGroups()

removeGroups

void removeGroups(String[] groups)
           throws RemoteException

Deletes a set of group names from this registration's managed set of groups.

After an invocation of this method results in the removal of one or more group names from the registration's managed set of groups, attempts to discover any lookup service that satisfies the following condition will cease to be made for this registration: the lookup service is a member of one or more of the removed group(s), but that lookup service is neither a member of any group in the resulting managed set of groups, nor does that lookup service correspond to any element in the registration's managed set of locators.

Parameters:

groups - a String array, none of whose elements may be null, consisting of the group names to delete from this registration's managed set of groups.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored.

If the empty set (equivalent to net.jini.discovery.LookupDiscovery.NO_GROUPS) is input, the registration's managed set of groups will not change.

If null (equivalent to net.jini.discovery.LookupDiscovery.ALL_GROUPS) is input, this method will throw a NullPointerException.

Throws:

UnsupportedOperationException - this exception occurs when the lookup discovery service has no managed set of groups associated with this registration.

NullPointerException - this exception occurs when either null (net.jini.discovery.LookupDiscovery.ALL_GROUPS) is input to the groups parameter, or one or more of the elements of the groups parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of groups may or may not have been successfully modified.

See Also:

addGroups(java.lang.String[])

addLocators

void addLocators(LookupLocator[] locators)
          throws RemoteException

Adds a set of LookupLocator objects to the managed set of locators associated with this registration.

For any new locator placed in the registration's managed set of locators as a result of an invocation of this method, if that locator equals no other locator corresponding to a previously discovered lookup service (across all registrations), the lookup discovery service will attempt unicast discovery of the lookup service associated with the new locator.

Parameters:

locators - an array, none of whose elements may be null, consisting of the LookupLocator objects with which to augment this registration's managed set of locators.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored. If any element of this parameter duplicates any element of this registration's managed set of locators, the duplicate will be ignored.

If the empty array is input, then this registration's managed set of locators will not change. If null is input, this method will throw a NullPointerException.

Throws:

UnsupportedOperationException - this exception occurs when the lookup discovery service has no managed set of locators associated with this registration.

NullPointerException - this exception occurs when either null is input to the locators parameter, or one or more of the elements of the locators parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of locators may or may not have been successfully augmented.

See Also:

removeLocators(net.jini.core.discovery.LookupLocator[])

setLocators

void setLocators(LookupLocator[] locators)
          throws RemoteException

Replaces all of the locators in this registration's managed set of locators with a new set of LookupLocator objects.

For any new locator placed in the managed set of locators as a result of an invocation of this method, if that locator equals no other locator corresponding to a previously discovered lookup service (across all registrations), the lookup discovery service will attempt unicast discovery of the lookup service associated with the new locator.

After an invocation of this method results in the removal (due to replacement) of a locator from the registration's managed set of locators, the action taken by the lookup discovery service can be described as follows: if the lookup service corresponding to the removed locator has yet to be discovered for this registration, attempts to perform locator discovery of that lookup service will cease; if that lookup service has already been discovered for this registration through locator discovery, but not through group discovery, the lookup service will be discarded.

Parameters:

locators - an array, none of whose elements may be null, consisting of the LookupLocator objects with which to replace the locators in this registration's managed set of locators.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored.

If the empty array is input, then locator discovery for this registration will cease. If null is input, this method will throw a NullPointerException.

Throws:

NullPointerException - this exception occurs when either null is input to the locators parameter, or one or more of the elements of the locators parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of locators may or may not have been successfully replaced.

See Also:

getLocators()

removeLocators

void removeLocators(LookupLocator[] locators)
             throws RemoteException

Deletes a set of of LookupLocator objects from this registration's managed set of locators.

After an invocation of this method results in the removal of a locator from the registration's managed set of locators, the action taken by the lookup discovery service can be described as follows: if the lookup service corresponding to the removed locator has yet to be discovered for this registration, attempts to perform locator discovery of that lookup service will cease; if that lookup service has already been discovered for this registration through locator discovery, but not through group discovery, the lookup service will be discarded.

Parameters:

locators - an array, none of whose elements may be null, consisting of the LookupLocator objects to remove from this registration's managed set of locators.

If any element of this parameter duplicates any other element of this parameter, the duplicate will be ignored.

If the empty set is input, the managed set of locators will not change. If null is input, this method will throw a NullPointerException.

Throws:

UnsupportedOperationException - this exception occurs when the lookup discovery service has no managed set of locators associated with this registration.

NullPointerException - this exception occurs when either null is input to the locators parameter, or one or more of the elements of the locators parameter is null.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, this registration's managed set of locators may or may not have been successfully modified.

See Also:

addLocators(net.jini.core.discovery.LookupLocator[])

discard

void discard(ServiceRegistrar registrar)
      throws RemoteException

Informs the lookup discovery service of the existence of an unavailable lookup service and requests that the lookup discovery service discard the unavailable lookup service.

When the lookup discovery service removes an already-discovered lookup service from a registration's managed set of lookup services and makes the lookup service eligible for re-discovery, the lookup service is considered to be "discarded". There are a number of situations where the lookup discovery service will discard a lookup service.

The lookup discovery service will discard a lookup service in response to a discard request resulting from an invocation of this method.

The lookup discovery service will discard a lookup service when the lookup service - previously discovered through locator discovery - is removed from a registration's managed set of locators in response to an invocation of either the setLocators method or the removeLocators method.

The lookup discovery service will discard a lookup service when the multicast announcements from an already-discovered lookup service are no longer being received.

Whenever the lookup discovery service discards a lookup service previously discovered for this registration, it will send an event to this registration's listener indicating that the lookup service has been discarded.

Note that if a lookup service crashes or is unavailable for some reason, there will be no automatic notification of the occurrence of such an event. This means that for each of a registration's targeted lookup services, after a lookup service is initially discovered, the lookup discovery service will not attempt to discover that lookup service again (for that registration) until that lookup service is discarded.

Thus, when a client determines that lookup service discovered for a registration is no longer available, it is the responsibility of the client to inform the lookup discovery service - through the invocation of this method - that the previously discovered lookup service is no longer available, and that attempts should be made to re-discover that lookup service for the registration. Typically, a client determines that a lookup service is unavailable when the client attempts to use the lookup service but receives a non-fatal exception or error (for example, a RemoteException) as a result of the attempt.

Parameters:

registrar - a reference to the lookup service that the lookup discovery service is being asked to discard.

If this parameter equals none of the lookup services contained in the managed set of lookup services for this registration, no action will be taken.

Throws:

NullPointerException - this exception occurs when null is input to the registrar parameter.

RemoteException - typically, this exception occurs when there is a communication failure between the client and the lookup discovery service. When this exception does occur, the lookup service may or may not have been successfully discarded.