	CS 696 Emerging Technologies: Java Distributed Computing Spring Semester, 1999 Simple Jini Example
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Contents of Doc 18, Simple Jini Example

References

Jini API, Local on-line version at: http://www-rohan.sdsu.edu/doc/jini/doc/api/index.html

Jini Entry Specification 1.0 January 25, 1999
Jini Entry Utilities Specification 1.0 January 25, 1999
Jini Lookup Service Specification 1.0 January 25, 1999
Jini Lookup Attribute Schema Specification 1.0 January 25, 1999

These documents are available at: http://www.sun.com/jini/specs/index.html

Noel Enete’s Nuggets for Jini, http://www.enete.com/download/index.html#_nuggets_


Doc 18, Simple Jini Example Slide # 2

Hello World Example

This example:

Uses a null lease
Uses unicast discovery & join
Is derived from an example in Noel Enete’s Nuggets for Jini

package whitney.jini.examples.hello;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface HelloInterface extends Remote 
   {
   public String sayHello() throws RemoteException;
   }
Doc 18, Simple Jini Example Slide # 3

HelloServer

package whitney.jini.examples.hello;
import net.jini.core.entry.Entry;
import net.jini.core.lookup.ServiceID;
import net.jini.lookup.entry.Name;
import com.sun.jini.lookup.ServiceIDListener;
import com.sun.jini.lookup.JoinManager;
import com.sun.jini.lease.LeaseRenewalManager;
import java.rmi.Remote;
import java.rmi.RemoteException;
import java.rmi.RMISecurityManager;
import java.rmi.server.UnicastRemoteObject;
public class HelloServer extends UnicastRemoteObject 
   implements HelloInterface, ServiceIDListener
   {
   private ServiceID myID;
   
   public HelloServer() throws RemoteException 
      {      }
   public String sayHello () throws RemoteException
      {
      return ("Hello World from Jini Hello server!");
      }
   public void serviceIDNotify (ServiceID uniqueID)
      {
      myID = uniqueID;
      System.out.println("server: ID set: " + myID );
      }
Doc 18, Simple Jini Example Slide # 4

HelloServer Main

   public static void main (String[] args) throws Exception
      {
      System.setSecurityManager (new RMISecurityManager ());
      HelloServer myServer = new HelloServer ();
      Entry[] identityingAttributes = new Entry[1];
      identityingAttributes[0] = new Name("HelloServer");
      JoinManager myManager = new JoinManager 
            (
            myServer, 
            identityingAttributes, 
            myServer, 
            new LeaseRenewalManager ()
            );
      System.out.println ("Server has been Joined!");
      }
   }
Doc 18, Simple Jini Example Slide # 5

HelloClient

package whitney.jini.examples.hello;
import net.jini.core.entry.Entry;
import net.jini.core.lookup.ServiceTemplate; 
import net.jini.core.lookup.ServiceRegistrar; 
import net.jini.core.discovery.LookupLocator;
import net.jini.lookup.entry.Name; 
import java.rmi.RMISecurityManager;
public class HelloClient
   {
   public static void main (String[] args) throws Exception
      {
      System.setSecurityManager (new RMISecurityManager ());
      LookupLocator lookup = new LookupLocator ("jini://eli.sdsu.edu");
      ServiceRegistrar registrar = lookup.getRegistrar ();
      
      Entry[] serverAttributes = new Entry[1];
      serverAttributes[0] = new Name ("HelloServer");
      ServiceTemplate template = 
         new ServiceTemplate (null, null, serverAttributes);
      HelloInterface myServerInterface = 
         (HelloInterface) registrar.lookup (template);
      System.out.println ( myServerInterface.sayHello () );
      }
   }
Doc 18, Simple Jini Example Slide # 6

Example Explained

The Client

   public static void main (String[] args) throws Exception
      {
      System.setSecurityManager (new RMISecurityManager ());
      LookupLocator lookup = new LookupLocator ("jini://eli.sdsu.edu");
      ServiceRegistrar registrar = lookup.getRegistrar();

Service Lookup

net.jini.core.discovery.LookupLocator
A utility class that performs unicast discovery for a Lookup service

Constructors LookupLocator(String url)
LookupLocator(String host, int port)

The URL type is jini
Default port for a lookup service is 4160
Translate CAFE-BABE from hex to decimal to get 4160

String getHost()
int getPort()
ServiceRegistrar getRegistrar()
ServiceRegistrar getRegistrar(int timeout)

Perform unicast discovery and return the ServiceRegistrar object for the given lookup service.


Doc 18, Simple Jini Example Slide # 7

Interface net.jini.core.lookup.ServiceRegistrar
Methods

Information about available services

Class[] getEntryClasses(ServiceTemplate tmpl) 
Object[] getFieldValues(ServiceTemplate, int setIndex, String field)
Class[] getServiceTypes(ServiceTemplate, String prefix)

Object lookup(ServiceTemplate tmpl) 
ServiceMatches lookup(ServiceTemplate tmpl, int maxMatches)

Returns the service object from an item matching the template

Information about Lookup service

String[] getGroups()

Returns the groups that this lookup service is a member of.

LookupLocator getLocator()

LookupLocator for unicast discovery of lookup service.

ServiceID getServiceID()

Notifcation, Registration

EventRegistration notify(ServiceTemplate tmpl, int transitions, 
   RemoteEventListener listener,  MarshalledObject handback, long leaseDuration)

ServiceRegistration register(ServiceItem item, long leaseDuration)
Doc 18, Simple Jini Example Slide # 8

HelloClient Continued


      // Create ServiceTemplate used to match or find the server
      // we want
      Entry[] serverAttributes = new Entry[1];
      serverAttributes[0] = new Name ("HelloServer");
      ServiceTemplate template = 
         new ServiceTemplate (null, null, serverAttributes);
      HelloInterface myServerInterface = 
         (HelloInterface) registrar.lookup (template);

Interface net.jini.core.entry.Entry

Entry subclasses:

Are used in identifying and matching services
Contains public fields of non-primitive types
Must have no-argument constructor
All fields must be serializable

Each field is serialized separately, so references between two fields of an entry will not be reconstituted to be shared references, but instead to separate copies of the original object
If a field of an entry being fetched is cannot be deserialized for any reason then net.jini.core.entry.UnusableEntryException will be thrown when

Entry is a marker interface, it has no methods


Doc 18, Simple Jini Example Slide # 9

Matching Entries

Let T (for template) be an object of a subclass Entry
Let E be an object of a subclass of Entry

A field of an Entry object is a wildcard it its value is null

The template T matches E if:

The type of E must be that of T, or be a subtype of the type of T

Fields with values in T must be matched exactly by the value in the same field of E.

Wildcards in T match any value in the same field of E.

MarshalledObject.equals is used to test equality of fields, not Object.equals

This means the bytes generated by their serialized form must match, ignoring differences of serialization stream implementation (such as blocking factors for buffering). Class version differences that change the bytes generated by serialization will cause objects not to match.


Doc 18, Simple Jini Example Slide # 10

net.jini.core.lookup.ServiceTemplate
Constructor

ServiceTemplate(ServiceID serviceID, Class[] serviceTypes, 
   Entry[] attrSetTemplates)

Public Fields Entry[] attributeSetTemplates
ServiceID serviceID
Class[] serviceTypes

ServiceTemplates are used to match for services

A service template (tmpl) matches service item (item) a if:

item.serviceID equals tmpl.serviceID

If tmpl.serviceID is null then tmpl and item match if:

item.service is an instance of every type in tmpl.serviceTypes

and item.attributeSets contains at least one matching entry for each entry template in tmpl.attributeSetTemplates.


Doc 18, Simple Jini Example Slide # 11

Standard Entry Subclasses

net.jini.lookup.entry Classes
Some basic entry classes with their fields. All fields are Strings

Address	ServiceInfo	Location	Name
country	manufacturer	building	name
locality	model	floor
organization	serialNumber	room
organizationalUnit	vendor		Comment
postalCode	version		comment
stateOrProvince
street

Status & StatusType
Status is base class from which other status-related entry classes may be derived.

StatusType defines status types:

ERROR
NORMAL
NOTICE
WARNING

net.jini.entry.AbstractEntry
Useful base class for entry types
You don’t have to use this class, but will save you some effort


Doc 18, Simple Jini Example Slide # 12

Entry & JavaBeans

Jini uses JavaBeans to display entry objects to humans

You should have a JavaBean class for an Entry class that a human may interact with

JavaBean Class Design Pattern Let X be an entry class then:

The JavaBean class for X is called XBean

For each field F in X class XBean has methods:

setF() and getF()

XBean has an no-argument constructor

XBean implements net.jini.lookup.entry.BeanEntry

XBean has methods followLink(), makeLink()

These methods set and get the bean’s field that contains the bean’s entry object

Location Entry Example Location fields and LocationBean’s methods

Location	LocationBean
building	Entry followLink()
floor	getBuilding()
room	getFloor()
	getRoom()
	makeLink(Entry e)
	setBuilding(String x)
	setFloor(String x)
	setRoom(String x)


Doc 18, Simple Jini Example Slide # 13

HelloClient Matching
The following code creates a simple template to use to find a service. The service id is set to null, so it is not used. Using the service ID would be faster, but we need to know it. We also set the serviceTypes to null. This means the template will match any serviceTypes. If we were looking for printers, we might set serviceTypes to be an array containing a printer type. Jini does not define these serviceTypes. They must be supplied by Jini developers. Only one entry template is given. Hence this service template will match any service that contains an entry of type "Name" or subtype of "Name" with the field "name" equal to the value "HelloServer".

      Entry[] serverAttributes = new Entry[1];
      serverAttributes[0] = new Name ("HelloServer");
      ServiceTemplate template = 
         new ServiceTemplate (null, null, serverAttributes);
      HelloInterface myServerInterface = 
         (HelloInterface) registrar.lookup (template);
Doc 18, Simple Jini Example Slide # 14

HelloServer


public class HelloServer extends UnicastRemoteObject 
   implements HelloInterface, ServiceIDListener
   {
   private ServiceID myID;
   
   public void serviceIDNotify (ServiceID uniqueID)
      {
      myID = uniqueID;
      System.out.println("server: ID set: " + myID );
      }

net.jini.core.lookup.ServiceID
Each service has a unique service id

The id is unique over time and space with respect to all other service ids generated by all lookup services. The id is a 128-bit value, to insure this uniqueness.

It is to be set by the lookup service.

To re-register an existing service, or to register the service in any other lookup service, item.serviceIDshould be set to the same service id that was returned by the initial registration.

com.sun.jini.lookup.ServiceIDListener
Contains one method, serviceIDNotify

The lookup service calls this method to provide the service its service ID.


Doc 18, Simple Jini Example Slide # 15

HelloServer Main

      HelloServer myServer = new HelloServer ();
      Entry[] identityingAttributes = new Entry[1];
      identityingAttributes[0] = new Name("HelloServer");
      JoinManager myManager = new JoinManager 
            (
            myServer, 
            identityingAttributes, 
            myServer, 
            new LeaseRenewalManager ()
            );

com.sun.jini.lookup.JoinManager
This class manages the join protocol for a service.
It discovers and keeps track of which lookup services to join, registers with them, keeps the registration leases renewed, and keeps the attributes up to date.

JoinManager(Object service, Entry[] attrSets,
ServiceIDListener callback, LeaseRenewalManager leaseMgr)


Doc 18, Simple Jini Example Slide # 16

JoinManager Methods
addAttributes(Entry[] attrSets)
addAttributes(Entry[] attrSets, boolean checkSC)

addGroups(String[] groups)
addLocators(LookupLocator[] locators)

Entry[] getAttributes()
String[] getGroups()

ServiceRegistrar[] getJoinSet()

Get the list of lookup services that have currently been joined.

LookupLocator[] getLocators()

Get the list of locators of specific lookup services to join.

modifyAttributes(Entry[] attrSetTemplates, Entry[] attrSets)
modifyAttributes(Entry[] attrSetTemplates, Entry[] attrSets, boolean checkSC)

removeGroups(String[] groups)
removeLocators(LookupLocator[] locators)

setAttributes(Entry[] attrSets)
setGroups(String[] groups)
setLocators(LookupLocator[] locators)
terminate()

Copyright ©, All rights reserved.
1999 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA.
OpenContent license defines the copyright on this document.

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