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RMI Registry

RMI Registry. Celsina Bignoli bignolic@smccd.net. 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

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RMI Registry

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  1. RMI Registry Celsina Bignoli bignolic@smccd.net

  2. 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 -> NAMING SERVICE

  3. 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

  4. 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

  5. bind(), rebind() and unbind() • parse name to find out where the registry is running • name is a URL with the following format //registryHost:port/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

  6. 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

  7. 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)

  8. 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

  9. 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)

  10. 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

  11. The Need for Directory Service • When there are many similar servers between which the user can choose • ex: choosing a printer based on features

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

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