Mini project /2 Jini - a new computing paradigm

Our first jini steps … basic topics: 1.RMI overview. 2.a first jini application: “ hello world ”. rmi

RMI-remote method invocation provides a way for Java applications running on different JVM ’ s/host computers to “ talk ” to each other.

basic ideas/concepts: 1.remote interface. 2.stubs and skeletons - rmic. client server Remote interface Remote impl stubskeleton

3.serialization. 4.parameters and return values. 5.dynamic code loading. 6.security implications. 7.marshaled objects. 8.the activation framework - rmid.

Jini basics

3 main components 1.service 2.client 3.jini environment - rmi,web server, lookup service...

service Device that shares its capabilities with other devices Devices Requirement –Memory & CPU –Connection to Network E.g. TV, Microwave,Printer,PC,Software

client A device that uses services Requirement –Memory & CPU –Connection to Network E.g. PDA, WAP Phone, PC, Coke Machine

The Jini environment Service Consumer Service Provider Jini Lookup Service

How does it works? 1.create the jini environment-lookup server online. 2.services discover,join and register on lookup servers. 3.clients discover and finds matching and downloading services, then using them.

Our first jini application - hello world! 1.compiling & running the jini env. 2.compiling & running a)server. b)client.

Creating The jini environment: 1.run a http server (jini provides a simple but efficient one) 2.run a rmi daemon (exists on Java 2) 3.run a lookup server (supplied with the reggie.jar files in jini)

Running the environment command lines: http server: java -jar java archive /usr/local/Java/jini1_1/lib/tools.jar jini’s http -port dir /usr/local/Java/jini1_1/lib the server’s root directory -verbose& Rmi daemon: rmid -J-Dsun.rmi.activation.execPolicy=none -port log /tmp/rmid_log& rmi log directory-recvering...

Running the environment command lines: Lookup server: java -Djava.security.policy=/usr/local/Java/jini1_1 /example/lookup/policy.all policy -jar /usr/local/Java/jini1_1/lib/reggie.jar lookup service codebase /usr/local/Java/jini1_1/example/lookup/policy.all /tmp/reggie_log1 public& policy

Compiling the server and client programs: Compile the server class: javac -classpath /usr/local/Java/jini1_1/lib/jini- core.jar:/usr/local/Java/jini1_1/lib/jini- ext.jar:/usr/local/Java/jini1_1/lib/sun- util.jar:/users/studs/bsc/2000/liyboviz/files/service -d /users/studs/bsc/2000/liyboviz/files/service /users/studs/bsc/2000/liyboviz/files/corejini/chapter5/HelloWorldS erviceInterface.java /users/studs/bsc/2000/liyboviz/files/corejini/chapter5/HelloWorldS ervice.java Compile the client class: javac -classpath /usr/local/Java/jini1_1/lib/jini- core.jar:/usr/local/Java/jini1_1/lib/jini- ext.jar:/usr/local/Java/jini1_1/lib/sun-util.jar: -d /users/studs/bsc/2000/liyboviz/files/client /users/studs/bsc/2000/liyboviz/files//corejini/chapter5/HelloWorld ServiceInterface.java /users/studs/bsc/2000/liyboviz/files/corejini/chapter5/HelloWorldC lient.java

Running - first the server, then the client: Server http: java -jar /usr/local/Java/jini1_1/lib/tools.jar -port dir /users/studs/bsc/2000/liyboviz/files/service-dl -verbose& The Service: java -cp /usr/local/Java/jini1_1/lib/jini- core.jar:/usr/local/Java/jini1_1/lib/jini- ext.jar:/usr/local/Java/jini1_1/lib/sun- util.jar:/users/studs/bsc/2000/liyboviz/files/service -Djava.rmi.server.codebase= -Djava.security.policy=/usr/local/Java/jini1_1/example/lookup /policy.all corejini.chapter5.HelloWorldService&

Running – then, the client: The Client: java -cp /usr/local/Java/jini1_1/lib/jini-core.jar: /usr/local/Java/jini1_1/lib/jini-ext.jar: /usr/local/Java/jini1_1/lib/sun-util.jar: /users/studs/bsc/2000/liyboviz/files/client -Djava.security.policy=/usr/local/Java/jini1_1/example/lookup /policy.all corejini.chapter5.HelloWorldClient&

Screen output From the service: >discovered a lookup service! >set serviceID to e91bb ty7554 From the client: >Got matching service. >Its message is: Hello, world!

What ’ s behind the screen?

The client/server known interface: // This is the interface that the service's proxy // implements package corejini.chapter5; public interface HelloWorldServiceInterface { public String getMessage(); }

The server ’ s code: // This is the first iteration of a Hello, World // service--it publishes a proxy that returns // a string when asked by clients. package corejini.chapter5; import net.jini.discovery.DiscoveryListener; import net.jini.discovery.DiscoveryEvent; import net.jini.discovery.LookupDiscovery; import net.jini.core.lookup.ServiceItem; import net.jini.core.lookup.ServiceRegistrar; import net.jini.core.lookup.ServiceRegistration; import java.util.Hashtable; import java.io.IOException; import java.io.Serializable; import java.rmi.RemoteException; import java.rmi.RMISecurityManager;

// This is the proxy object that will be downloaded // by clients. It's serializable and implements // our well-known HelloWorldServiceInterface. class HelloWorldServiceProxy implements Serializable, HelloWorldServiceInterface { public HelloWorldServiceProxy() { } public String getMessage() { return "Hello, world!"; }

// HelloWorldService is the "wrapper" class that // handles publishing the service item. public class HelloWorldService implements Runnable { // 10 minute leases protected final int LEASE_TIME = 10 * 60 * 1000; protected Hashtable registrations = new Hashtable(); protected ServiceItem item; protected LookupDiscovery disco; // Inner class to listen for discovery events class Listener implements DiscoveryListener { // Called when we find a new lookup service. public void discovered(DiscoveryEvent ev) { System.out.println("discovered a lookup service!"); ServiceRegistrar[] newregs = ev.getRegistrars(); for (int i=0 ; i<newregs.length ; i++) { if (!registrations.containsKey(newregs[i])) { registerWithLookup(newregs[i]); }}}

// Called ONLY when we explicitly discard a // lookup service, not "automatically" when a // lookup service goes down. Once discovered, // there is NO ongoing communication with a // lookup service. public void discarded(DiscoveryEvent ev) { ServiceRegistrar[] deadregs = ev.getRegistrars(); for (int i=0 ; i<deadregs.length ; i++) { registrations.remove(deadregs[i]);}}} public HelloWorldService() throws IOException { item = new ServiceItem(null, createProxy(), null); // Set a security manager if (System.getSecurityManager() == null) { System.setSecurityManager(new RMISecurityManager());} // Search for the "public" group, which by // convention is named by the empty string disco = new LookupDiscovery(new String[] { "" }); // Install a listener. disco.addDiscoveryListener(new Listener()); }

protected HelloWorldServiceInterface createProxy() { return new HelloWorldServiceProxy();} // This work involves remote calls, and may take a while to complete //Thus, since it's called from discovered(), it will prevent us // from responding in a timely fashion to new discovery events. An // improvement would be to spin off a separate short- // lived thread to do the work. protected synchronized void registerWithLookup(ServiceRegistrar registrar) { ServiceRegistration registration = null; try { registration = registrar.register(item, LEASE_TIME); } catch (RemoteException ex) { System.out.println("Couldn't register: " + ex.getMessage()); return;} if (item.serviceID == null) { item.serviceID = registration.getServiceID(); System.out.println("Set serviceID to " + item.serviceID);} registrations.put(registrar, registration); }

// This thread does nothing but sleep, but it // makes sure the VM doesn't exit. public void run() { while (true) { try { Thread.sleep( ); } catch (InterruptedException ex) { }}} // Create a new HelloWorldService and start // its thread. public static void main(String args[]) { try { HelloWorldService hws = new HelloWorldService(); new Thread(hws).start(); } catch (IOException ex) { System.out.println("Couldn't create service: " + ex.getMessage());}}}

The client ’ s code: // A simple Client to exercise the HelloWorldService package corejini.chapter5; import net.jini.discovery.DiscoveryListener; import net.jini.discovery.DiscoveryEvent; import net.jini.discovery.LookupDiscovery; import net.jini.core.lookup.ServiceRegistrar; import net.jini.core.lookup.ServiceTemplate; import java.util.Vector; import java.io.IOException; import java.rmi.RemoteException; import java.rmi.RMISecurityManager;

public class HelloWorldClient implements Runnable { protected ServiceTemplate template; protected LookupDiscovery disco; // An inner class to implement DiscoveryListener class Listener implements DiscoveryListener { public void discovered(DiscoveryEvent ev) { ServiceRegistrar[] newregs = ev.getRegistrars(); for (int i=0 ; i<newregs.length ; i++) { lookForService(newregs[i]); } public void discarded(DiscoveryEvent ev) { }

public HelloWorldClient() throws IOException { Class[] types = { HelloWorldServiceInterface.class }; template = new ServiceTemplate(null, types, null); // Set a security manager if (System.getSecurityManager() == null) { System.setSecurityManager(new RMISecurityManager()); } // Only search the public group disco = new LookupDiscovery(new String[] { "" }); // Install a listener disco.addDiscoveryListener(new Listener()); }

// Once we've found a new lookup service, search // for proxies that implement // HelloWorldServiceInterface protected Object lookForService(ServiceRegistrar lusvc) { Object o = null; try { o = lusvc.lookup(template); } catch (RemoteException ex) { System.err.println("Error doing lookup: " + ex.getMessage()); return null;} if (o == null) { System.err.println("No matching service."); return null; } System.out.println("Got a matching service."); System.out.println("It's message is: " + ((HelloWorldServiceInterface) o).getMessage()); return o;}

// This thread does nothing--it simply keeps the // VM from exiting while we do discovery. public void run() { while (true) { try { Thread.sleep( ); } catch (InterruptedException ex) { }}} // Create a HelloWorldClient and start its thread public static void main(String args[]) { try { HelloWorldClient hwc = new HelloWorldClient(); new Thread(hwc).start(); } catch (IOException ex) { System.out.println("Couldn't create client: " + ex.getMessage()); }}}

A policy file example grant { // Allow everything for now permission java.security.AllPermission; };

The End To be continued...