DU341 The DiscoveryManagement Interfaces in Java

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DU341 The DiscoveryManagement Interfaces
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The LookupDiscovery class implements both the DiscoveryManagement and the DiscoveryGroupManagement interfaces, which together define methods related to the coordination and management of all group discovery processing See Section DU2, "The Discovery Management Interfaces" for more information on those interfaces
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DU342 Security and Multicast Discovery: The DiscoveryPermission Class
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When an instance of the LookupDiscovery class is constructed, the entity that creates the instance must be granted appropriate discovery permission For example, if the instance of LookupDiscovery is currently configured to discover a non empty, nonnull set of groups, then the entity that created the instance must have permission to attempt discovery of each of the groups in that set If the set of groups to discover is null (ALL_GROUPS), then the entity must have permission to attempt discovery of all possible groups If appropriate permissions are not granted, the constructor of LookupDiscovery, as well as the methods addGroups and setGroups, will throw a DU3 LookupDiscovery Utility 178
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O'Reilly Network Safari Bookshelf Jini Specifications, The, Second Edition javalangSecurityException Discovery permissions are controlled in security policy files using the permission class DiscoveryPermission The public methods provided by the DiscoveryPermission class are as follows:
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package netjinidiscovery; public final class DiscoveryPermission extends Permission implements Serializable { public DiscoveryPermission(String group) {} public DiscoveryPermission(String group, String actions) {} }
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The DiscoveryPermission class is a subclass of Permission, adding no additional items of abstract state
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The Semantics
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The equals method for this class returns true if and only if two instances of this class have the same group name The constructor for this class has two forms: one form expecting one input parameter, the other form expecting two input parameters Each form of the constructor takes, as its first input parameter, a String representing one or more group names for which to allow discovery The second parameter of the second form of the constructor is a String value that is currently ignored because there are no actions associated with a discovery permission
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DiscoveryPermission Examples
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A number of examples that illustrate the use of this permission are presented Note that each example represents a line in a policy file
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permission netjinidiscoveryDiscoveryPermission "*";
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Grant the entity permission to attempt discovery of all possible groups
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permission netjinidiscoveryDiscoveryPermission "";
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Grant the entity permission to attempt discovery of only the "public" group
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permission netjinidiscoveryDiscoveryPermission "foo";
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Grant the entity permission to attempt discovery of the group named "foo"
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permission netjinidiscoveryDiscoveryPermission "*suncom";
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Grant the entity permission to attempt discovery of all groups whose names end with the substring "suncom" Each of the above declarations grants permission to attempt discovery of one name A name does not necessarily correspond to a single group That is, the following should be noted: The name "*" grants permission to attempt discovery of all possible groups A name beginning with "*" grants permission to attempt discovery of all groups that match the remainder of that name; for example, the name "*exampleorg" would match a group named "foonlyexampleorg" and also a group named "sfcaexampleorg" DU3 LookupDiscovery Utility 179
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O'Reilly Network Safari Bookshelf Jini Specifications, The, Second Edition The empty name "" denotes the public group All other names are treated as individual groups and must match exactly Finally, it is important to note that a restriction of the Java platform security model requires that appropriate DiscoveryPermission be granted to the Jini technology infrastructure software codebase itself, in addition to any codebases that may use Jini technology infrastructure software classes DU35 Serialized Forms
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DU3 LookupDiscovery Utility
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Section: DU Jini Discovery Utilities Specification
DU4 The LookupLocatorDiscovery Utility
DU41 Overview The The Jini Technology Core Platform Specification, "Discovery and Join", states that the "unicast discovery protocol is a simple request response protocol" In a Jini application environment, the entities that participate in this protocol are a discovering entity (Jini client or service) and a Jini lookup service that acts as the entity to be discovered The discovering entity sends unicast discovery requests to the lookup service, and the lookup service reacts to those requests by sending unicast discovery responses to the interested discovering entity The LookupLocatorDiscovery helper utility (belonging to the package netjinidiscovery) encapsulates the functionality required of an entity that wishes to employ the unicast discovery protocol to discover a lookup service This utility provides an implementation that makes the process of finding specific instances of a lookup service much simpler for both services and clients Because the LookupLocatorDiscovery helper utility class will participate in only the unicast discovery protocol, and because the unicast discovery protocol imposes no restriction on the physical location of a service or client relative to a lookup service, this utility can be used to discover lookup services running on hosts that are located far from, or near to, the hosts on which the service is running This lack of a restriction on location brings with it a requirement that the discovering entity supply specific information about the desired lookup services to the LookupLocatorDiscovery utility; namely, the location of the device(s) hosting each lookup service This information is supplied through an instance of the LookupLocator utility, defined in The Jini Technology Core Platform Specification, "Discovery and Join" It may be of value to note the difference between LookupLocatorDiscovery and the LookupDiscovery helper utility for group discovery (defined earlier) Although both are non remote utility classes that entities can use to discover at least one lookup service, the LookupLocatorDiscovery utility is designed to provide discovery capabilities that satisfy different needs than those satisfied by the LookupDiscovery utility These two utilities differ in the following ways: Whereas the LookupLocatorDiscovery utility is used to discover lookup services by their locators, employing the unicast discovery protocol, the LookupDiscovery utility uses the multicast discovery protocols to discover lookup services by the groups to which the lookup services belong Whereas the LookupLocatorDiscovery utility requires that the discovering entity supply the specific location or address of the desired lookup service(s) in the form of a LookupLocator object, the LookupDiscovery utility imposes no such restriction on the discovering entity Whereas the LookupLocatorDiscovery utility can be used by a discovering entity to discover lookup services that are both "near" and "far," the LookupDiscovery utility can be used to discover only those lookup services that are located within the same multicast radius as that of the discovering entity DU42 Other Types The types defined in the specification of the LookupLocatorDiscovery utility class are in the netjinidiscovery package The following additional types may also be referenced in this DU4 The LookupLocatorDiscovery Utility 181
O'Reilly Network Safari Bookshelf Jini Specifications, The, Second Edition specification Whenever referenced, these object types will be referenced in unqualified form:
netjinicorediscoveryLookupLocator netjinidiscoveryDiscoveryManagement netjinidiscoveryDiscoveryLocatorManagement
DU43 The Interface The public methods provided by the LookupLocatorDiscovery class are as follows:
package netjinidiscovery; public class LookupLocatorDiscovery implements DiscoveryManagement DiscoveryLocatorManagement { public LookupLocatorDiscovery (LookupLocator[] locators) {} public LookupLocator[] getDiscoveredLocators() {} public LookupLocator[] getUndiscoveredLocators() {} }
DU44 The Semantics Including the constructor, the LookupLocatorDiscovery helper utility class defines three new public methods All other public methods are inherited from the DiscoveryManagement and DiscoveryLocatorManagement interfaces Each instance of the LookupLocatorDiscovery class must behave as if it operates independently of all other instances The equals method for this class returns true if and only if two instances of this class refer to the same object That is, x and y are equal instances of this class if and only if x==y has the value true The constructor of the LookupLocatorDiscovery class takes a single input parameter: a set of locators represented as an array of LookupLocator objects, none of whose elements may be null Each element in the input set corresponds to a specific lookup service the discovering entity wishes to be discovered Although it is acceptable to input null, if a nonnull array containing at least one null element is input, a NullPointerException will be thrown Invoking the constructor with an input array that contains duplicate locators (as determined by LookupLocatorequals) is equivalent to performing the invocation with the duplicates removed from the array Although discovery events will not be sent by this class until a listener is added through an invocation of the addListener method, discovery processing usually starts as soon as an instance of this class is constructed However, if null or an empty array is passed to the constructor, discovery will not be started until the addLocators or setLocators method is called to change the managed set of locators to a set of locators that is nonnull and non empty The getDiscoveredLocators method returns the set of LookupLocator objects representing the desired lookup services that are currently discovered If the set is empty, this method will return an empty array This method takes no arguments as input, and will return a new array upon each invocation The getUndiscoveredLocators method returns the set of LookupLocator objects representing the desired lookup services that have not yet been discovered If the set is empty, this method will return an empty array This method takes no arguments as input, and will return a new array upon each invocation