net.jini.discovery

Class LookupDiscovery

java.lang.Object

net.jini.discovery.LookupDiscovery

All Implemented Interfaces:

DiscoveryGroupManagement, DiscoveryManagement

public class LookupDiscovery
extends Object
implements DiscoveryManagement, DiscoveryGroupManagement

This class is a helper utility class that encapsulates the functionality required of an entity that wishes to employ multicast discovery to find lookup services located within the entity's "multicast radius" (roughly, the number of hops beyond which neither the multicast requests from the entity, nor the multicast announcements from the lookup service, will propagate). This class helps make the process of acquiring references to lookup services - based on no information other than lookup service group membership - much simpler for both services and clients.

Author:

Sun Microsystems, Inc.

See Also:

ServiceRegistrar, DiscoveryChangeListener, DiscoveryManagement, DiscoveryGroupManagement, DiscoveryListener, DiscoveryEvent, DiscoveryPermission

Field Summary

Fields

Modifier and Type	Field and Description
static String[]	ALL_GROUPS Convenience constant used to request that attempts be made to discover all lookup services that are within range, and which belong to any group.
static String[]	NO_GROUPS Convenience constant used to request that discovery by group membership be halted (or not started, if the group discovery mechanism is simply being instantiated).

Constructor Summary

Constructors

Constructor and Description
LookupDiscovery(String[] groups) Construct a new lookup discovery object, set to discover the given set of groups.
LookupDiscovery(String[] groups, Configuration config) Constructs a new lookup discovery object, set to discover the given set of groups, and having the given Configuration.

Method Summary

Modifier and Type	Method and Description
void	addDiscoveryListener(DiscoveryListener l) Register a listener as interested in receiving DiscoveryEvent notifications.
void	addGroups(String[] newGroups) Add a set of groups to the set to be discovered.
void	discard(ServiceRegistrar reg) Discard a registrar from the set of registrars already discovered.
String[]	getGroups() Return the set of group names this LookupDiscovery instance is trying to discover.
ServiceRegistrar[]	getRegistrars() Returns an array of instances of ServiceRegistrar, each corresponding to a proxy to one of the currently discovered lookup services.
void	removeDiscoveryListener(DiscoveryListener l) Indicate that a listener is no longer interested in receiving DiscoveryEvent notifications.
void	removeGroups(String[] oldGroups) Remove a set of groups from the set to be discovered.
void	setGroups(String[] newGroups) Change the set of groups to be discovered to correspond to the given set.
void	terminate() Terminate the discovery process.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ALL_GROUPS

public static final String[] ALL_GROUPS

Convenience constant used to request that attempts be made to discover all lookup services that are within range, and which belong to any group. Must define this constant here as well as in DiscoveryGroupManagement for compatibility with earlier releases.

NO_GROUPS

public static final String[] NO_GROUPS

Convenience constant used to request that discovery by group membership be halted (or not started, if the group discovery mechanism is simply being instantiated). Must define this constant here as well as in DiscoveryGroupManagement for compatibility with earlier releases.

Constructor Detail

LookupDiscovery

public LookupDiscovery(String[] groups)
                throws IOException

Construct a new lookup discovery object, set to discover the given set of groups. The set is represented as an array of strings. This array may be empty, which is taken as the empty set, and discovery is not performed. The reference passed in may be null, which is taken as no set, and in which case discovery of all reachable lookup services is performed. Otherwise, the array contains the names of groups to discover. The caller must have DiscoveryPermission for each group (or for all groups, if the array is null).

Parameters:

groups - the set of group names to discover (null for no set, empty for no discovery)

Throws:

NullPointerException - input array contains at least one null element

IOException - an exception occurred in starting discovery

See Also:

NO_GROUPS, ALL_GROUPS, setGroups(java.lang.String[]), DiscoveryPermission

LookupDiscovery

public LookupDiscovery(String[] groups,
                       Configuration config)
                throws IOException,
                       ConfigurationException

Constructs a new lookup discovery object, set to discover the given set of groups, and having the given Configuration.

The set of groups to discover is represented as an array of strings. This array may be empty, which is taken as the empty set, and discovery is not performed. The reference passed in may be null, which is taken as no set, and in which case discovery of all reachable lookup services is performed. Otherwise, the array contains the names of groups to discover. The caller must have DiscoveryPermission for each group (or for all groups, if the array is null).

Parameters:

groups - the set of group names to discover (null for no set, empty for no discovery)

config - an instance of Configuration, used to obtain the objects needed to configure the current instance of this class

Throws:

NullPointerException - input array contains at least one null element or null is input for the configuration

IOException - an exception occurred in starting discovery

ConfigurationException - indicates an exception occurred while retrieving an item from the given Configuration

See Also:

NO_GROUPS, ALL_GROUPS, setGroups(java.lang.String[]), DiscoveryPermission, Configuration, ConfigurationException

Method Detail

addDiscoveryListener

public void addDiscoveryListener(DiscoveryListener l)

Register a listener as interested in receiving DiscoveryEvent notifications.

Specified by:

addDiscoveryListener in interface DiscoveryManagement

Parameters:

l - the listener to register

Throws:

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

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

DiscoveryEvent, removeDiscoveryListener(net.jini.discovery.DiscoveryListener)

removeDiscoveryListener

public void removeDiscoveryListener(DiscoveryListener l)

Indicate that a listener is no longer interested in receiving DiscoveryEvent notifications.

Specified by:

removeDiscoveryListener in interface DiscoveryManagement

Parameters:

l - the listener to unregister

Throws:

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

addDiscoveryListener(net.jini.discovery.DiscoveryListener)

getRegistrars

public ServiceRegistrar[] getRegistrars()

Returns an array of instances of ServiceRegistrar, each corresponding to a proxy to one of the currently discovered lookup services. For each invocation of this method, a new array is returned.

Specified by:

getRegistrars in interface DiscoveryManagement

Returns:

array of instances of ServiceRegistrar, each corresponding to a proxy to one of the currently discovered lookup services

Throws:

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

ServiceRegistrar, DiscoveryManagement.removeDiscoveryListener(net.jini.discovery.DiscoveryListener)

discard

public void discard(ServiceRegistrar reg)

Discard a registrar from the set of registrars already discovered. This does not prevent that registrar from being rediscovered; it is intended to be used to clear unreachable entries from the set.

If the registrar has been discovered using this LookupDiscovery object, each listener registered with this object will have its discarded method called with the given registrar as parameter.

Specified by:

discard in interface DiscoveryManagement

Parameters:

reg - the registrar to discard

Throws:

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

DiscoveryListener.discarded(net.jini.discovery.DiscoveryEvent)

terminate

public void terminate()

Terminate the discovery process.

Specified by:

terminate in interface DiscoveryManagement

getGroups

public String[] getGroups()

Return the set of group names this LookupDiscovery instance is trying to discover. If this method returns the empty array, that value is guaranteed to be referentially equal to LookupDiscovery.NO_GROUPS.

Specified by:

getGroups in interface DiscoveryGroupManagement

Returns:

the set of groups to be discovered (null for all, empty for no discovery)

Throws:

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

NO_GROUPS, ALL_GROUPS, setGroups(java.lang.String[])

addGroups

public void addGroups(String[] newGroups)
               throws IOException

Add a set of groups to the set to be discovered. The caller must have DiscoveryPermission for each group.

Specified by:

addGroups in interface DiscoveryGroupManagement

Parameters:

newGroups - the groups to add

Throws:

IOException - the multicast request protocol failed to start

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

UnsupportedOperationException - there is no set of groups to add to

See Also:

DiscoveryPermission

setGroups

public void setGroups(String[] newGroups)
               throws IOException

Change the set of groups to be discovered to correspond to the given set. The set is represented as an array of strings. This array may be empty, which is taken as the empty set, and discovery is not performed. The reference passed in may be null, which is taken as no set, and in which case discovery of all reachable lookup services is performed. Otherwise, the array contains the names of groups to discover. The caller must have DiscoveryPermission for each group (or for all groups, if the array is null).

Specified by:

setGroups in interface DiscoveryGroupManagement

Parameters:

newGroups - the new set of groups to discover (null for all, empty array for no discovery)

Throws:

IOException - an exception occurred when starting multicast discovery

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

See Also:

LookupDiscovery(java.lang.String[], net.jini.config.Configuration), ALL_GROUPS, NO_GROUPS, DiscoveryPermission, getGroups()

removeGroups

public void removeGroups(String[] oldGroups)

Remove a set of groups from the set to be discovered.

Specified by:

removeGroups in interface DiscoveryGroupManagement

Parameters:

oldGroups - groups to remove

Throws:

IllegalStateException - this exception occurs when this method is called after the terminate method has been called.

UnsupportedOperationException - there is no set of groups from which to remove

See Also:

DiscoveryGroupManagement.addGroups(java.lang.String[])