The Jini Technology Lookup Service

1
The Jini Technology Lookup Service
2
How Does It Work

• Services and clients find a lookup service using
  the discovery protocol
• Services advertise themselves by registering with
  the lookup service
• Clients query the lookup service to find the
  services they need
• Peer-to peer communication between client and
  service after that

3
Discovery/Join and Lookup Protocols
Figure 1 Discovery
4
Discovery/Join and Lookup Protocols
Figure 2 Join
5
Discovery/Join and Lookup Protocols
Figure 3 Lookup
6
Discovery/Join and Lookup Protocols
Figure 4 Service Invocation
7
Discovery and Join

• How does a client or service find lookup services
• How does a service join a lookup service
• How does a client know which ones to do lookups in

8
Initial Discovery

• Performed by both clients and services
• Send multicast request packet
• Groups you are looking for
• Host and TCP port to use contact you
• Waiting for lookup services to connect back
• Download lookup services proxy object
• Register with or do lookup in

9
Lookup Service

• Network service
• For finding other network services
• Workgroup-scale, not the entire Internet
• Not a naming or directory service
• Focus is on types, not names
• Yellow pages, not white pages
• Both programmatic and end-user access

10
Lookup Service 101

• Each service registers its proxy object
• Client does lookup by interface type
• Instance of semantics
• API uses java.lang.Class instances, not strings
• Client gets proxy object back
• Needed classes are automatically downloaded
• Proxy communicates with remote service

11
Service Type Matching

• Can match on any type
• Interface or concrete class
• Including super interface or superclass
• Can get subinterface or subclass back
• Java.lang.Object match everything
• Can match using multiple types

12
Service Type Matching

• I want a combination TV/VCR
• org.Ce.TV AND org.Ce.VCR
• Yellow pages
• Automatic placement in all categories
• Base class and all interfaces
• All superclasses and superinterfaces

13
Attributes

• Service can also register with attributes
• Attributes allow further discrimination between
  services of the same type
• Lookup support matching on
• Just service types
• Just attributes
• Combinations

14
Example Generic Attributes

• Name
• Location
• Manufacturer
• Model

15
Example Printer Attributes (1)

• Monochrome or color
• Resolution
• Speed
• Paper size

16
Attribute Characteristics

• Some are defined by service itself
• e.g., manufacturer, model, resolution
• Some are defined by administrator
• e.g., Name, location
• Attributes can have multiple values

17
Example Printer Attributes (2)

• Printer supports these combinations
• Monochrome, 600 dpi, 10 ppm
• Monochrome, 300 dpi, 15 ppm
• Color, 300 dpi, 5 ppm
• For each combination, printer supports
• Letter
• Legal
• Envelope

18
Attribute Representation

• Each attribute is a public field of a class
• Attribute name field name
• Attribute type field type
• Each class defines an attribute set
• Co-dependent attributes in the same class
• Orthogonal attributes in different classes
• Each service has set of attribute sets
• Instances of multiple classes
• Multiple instances of the same class

19
Example Printer Attribute (3)

• PrintEnginecolor false, dpi 600, ppm 10
• PrintEnginecolor false, dpi 300, ppm 15
• PrintEnginecolor false, dpi 300, ppm 5
• PaperSizesize PaperType.Letter
• PaperSizesize PaperType.Legal
• PaperSizesize PaperType.Envelope
• Locationfloor 3, room 1234, building
  A1
• Namename rainbow

20
Attribute Set Matching

• Match on attribute set class
• Including superclasses
• Match on attribute values (fields)
• Exact value match only
• java.rmi.MarshalledObject.equals
• Template is just an attribute set instance
• Null field match any value (wildcard)

21
Matching Examples

• template PrintEnginecolor false, dpi null,
• ppm null
• matches PrintEnginecolor false, dpi 600, ppm
  10
• and PrintEnginecolor false, dpi 300, ppm
  15

22
Matching Examples

• template PrintAttrs
• matches PrintEnginecolor true, dpi 300,
• ppm 5
• and PageSizesize Legal

23
Service Registration

• Service registers by providing
• Service id
• Every service has a universally unique id
• Lookup service will assign one if requested
• Proxy object
• Zero or more attribute sets

24
Service Registration

• public class ServiceItem implements
• java.io.Serializable
• public ServiceID serviceID
• public Object service
• public Entry attributeSets

25
Service Template

• Service template contains
• Optional service id
• Null is wildcard match any
• Zero or more service types
• Zero or more attribute set templates
• Null fields are wildcards match any

26
Service Template

• public class ServiceTemplate implements
• java.io.Serializable
• public ServiceID serviceID
• public Class serviceTypes
• public Entry attributeSetTemplates

27
Template Matching

• Service registration matches template if
• Service id matches, and
• Proxy is instance of each service type, and
• For each attribute set template
• Service has a matching attribute set

28
Example Queries

• Any service named rainbow
• Any Printer named rainbow in A1
• Any color envelope Printer
• All services on floor 3

29
Complex Queries

• Between 300 and 600 dpi
• On floor 1, 3, or 7
• Letter or Legal
• Printer or Copier

30
Complex Queries

• Technique 1
• Change ranges and ors to wildcards
• Do single template-based lookup
• Then do finer-grained match locally
• Technique 2
• Query for actual values in ranges and ors
• Do multiple lookups

31
Attribute Modification

• Can only be done by service itself
• Allows service to control policy
• Internal state changes
• Administrative interfaces
• Service is responsible for persistent storage
• Add, modify, delete, replace all
• Attributes should change infrequently
• Primary search keys
• Query service directly for very dynamic state

32
Lookup Groups

• Each lookup service is configured with s set of
  group names
• Is in (is a member of) each group
• Each service is configured with a set of group
  names
• Registers with all lookup services in any of
  those groups
• Each client is configured with a set of group
  names
• Uses lookup service in any of those groups

33
Summary

• Service perspective
• Register with desired attributes
• Keep renewing registration lease
• Add, modify, delete attributes as desired
• Client perspective
• Lookup any 1 of
• Get just proxy object
• Lookup to N of
• Get proxies attributes, and service IDS