RMI Registry

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RMI Registry
Celsina Bignoli bignolic_at_smccd.net
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Bootstrapping Problem

• clients on a machine need to connect to servers
  on another machine
• How does the client know where the server is?
• server location hard-coded in client code or
  stored in a configuration file
• user tells client where server is located
• use a service in a well-known location as a point
  of indirection -gt NAMING SERVICE

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Why using Naming Services

• servers migrate
• there may be many servers
• servers are partitioned and replicated
• there may be many servers running on a machine

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RMI Registry

• methods are in java.rmi.Naming class
• public static void bind(String name, Remote
  object)
• public static void rebind(String name, Remote
  object)
• public static void unbind(String name)
• public static String list(String name)
• public static Remote lookup(String name)
• above methods are declared in interface
  java.rmi.registry.Registry which extends
  java.rmi.Remote and implemented by
  sun.rmi.registry.RegistryImpl

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bind(), rebind() and unbind()

• parse name to find out where the registry is
  running
• name is a URL with the following format
• //registryHostport/logical_name
• Host optional (defaults to localhost)
• port optional (defaults to 1099)
• open socket to registry (which is a server
  running on the specified host and listening on
  the indicated port)
• serialize stub implementing remote object
• bind it to name

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lookup() and list()

• name is a URL as for bind().
• name for list() only specifies the host and port
  where the registry is located
• lookup() returns the stub bound to it
• list() returns complete URLs of all servers bound
  to the registry
• see code example

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RMI Registry is a RMI Server

• Underlying Naming static methods there are a
  Remote interface and its implementation class
• java.rmi.registry.Registry (interface)
• defines 5 methods each of which maps to the
  corresponding static method in Naming
• java.rmi.registry.RegistryImpl (class)

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How Naming works

• a static method on naming is called with a given
  URL
• URL is parsed and the machine/port information is
  to class LocateRegistry which has methods for
  returning the stub for the given registry
• Naming uses this stub to invoke the appropriate
  method on the registry

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Application-specific Registry

• start a registry at an application-specific port
• using the rmiregistry program
• rmiregistry 10345
• from within the code, using static method of
  LocateRegistry class
• public static createRegistry(int port)

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Advantages of the RMI Registry

• easy to administer
• launch it with rmiregistry, provided as part of
  the JDK distribution
• easy for clients to find
• only need to know on which machine it runs
• easy for clients to use
• only 5 easy to use methods
• fast

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The Need for Directory Service

• When there are many similar servers between which
  the user can choose
• ex choosing a printer based on features

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Security Issues

• Each process binding a server to the registry
  must run on the same machine where the registry
  runs