Generic architecture

Transcription

1 Java-RMI Lab

2 Outline Let first builds a simple home-made framework This is useful to understand the main issues We see later how java-rmi works and how it solves the same issues

3 Generic architecture object A client proxy for B Request server skeleton & dispatcher for B s class remote object B Reply Remote reference module Communication module Communication module Remote reference module servant Local proxy: Remote methods appear as local Remote Reference Module: local-remote object map Dispatcher: Dispatch the request to a Skeleton Skeleton: Invoke the method on B; send back the reply

4 Implementation We d like something like this client proxy for Counter object A Receive input Client Object Remote reference module Communication module Call method on the proxy

5 Implementation Proxy object A client proxy for Counter public int inc(int value){ //marshal value //prepare a request //send the request to the Server //The address is in the //Remote Reference Module Remote reference module Communication module // on in a remote reference data structure } public int dec(int value){ }

6 Implementation Communication module Communication module server remote skeleton object B & dispatcher for B s class servant Remote reference module Register an object (uses Object Table) Dispatch to the Skeleton Initialize Communication Module Receive request

7 Implementation Skeleton server skeleton & dispatcher for B s class remote object B Initialize (bound to a Counter) Dispatch to the Object Skeleton & Dispatcher Communication module Remote reference module servant Receive request Send the reply

8 Implementation details See RMI-LAB on the web site Exercise: add a new object

9 Lesson learned Key (and borrowing) aspects Managing communication Managing remote reference Implements support modules (proxy, skeleton)

10 Java-rmi solution Managing communication Embedded into the JVM Managing remote reference Rmiregistry, remote reference layer Implements support modules (proxy, skeleton) Proxy: automatically generated from the code Skeleton: no longer needed thanks to reflection (see later)

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12 Lab1: Remote counter import java.rmi.*; //Import rmi API public interface Counter extends Remote //makes Counter a remote interface { int inc(int i) throws RemoteException; //manage or throws this exception. int dec(int i) throws RemoteException; }

13 Step2: interface implementation import java.rmi.*; public class Counter_impl implements Counter { private int counter; } public Counter_impl() throws RemoteException {counter = 0;} public int inc(int i) throws RemoteException {counter++;return counter;} public int dec(int i) throws RemoteException {counter--;return counter;}

14 import java.rmi.remoteexception; import java.rmi.server.unicastremoteobject; import java.rmi.registry.locateregistry; import java.rmi.registry.registry; public class Server { public static void main(string args[]) throws RemoteException { //Create a remote object.. Counter c = new Counter_impl() ; Counter stub = (Counter)UnicastRemoteObject.exportObject(c, 0); Export object = It can receive requests } //bind "counter" to the stub Registry registry = LocateRegistry.getRegistry(); registry.rebind("counter", stub); System.out.println("Counter bound"); }

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16 Client import java.rmi.remoteexception; import java.rmi.registry.locateregistry; import java.rmi.registry.registry; public class Client { public static void main(string args[]) { try{ Registry registry = LocateRegistry.getRegistry(args[0]); Counter c = (Counter) registry.lookup("counter"); int i = c.inc(10); System.out.println(i); } catch (Exception e){e.printstacktrace();} } }

17 Running the example On the same machine via classpath Run rmiregisrty: rmiregistry (make sure CLASSPATH is unset) Run the server: java -classpath. Server Run the client: java -classpath. Client localhost

18 Class downloading JAVA-RMI allows to download the definition of an object's class if the class is not defined in the receiver's Java virtual machine. Classes definitions are typically made network accessible through a web server

19 Class downloading are controlled by a Security manager Without a security manager installed, RMI will not download classes, other than from the local class path. This restriction ensures that the operations performed by downloaded code are subject to a security policy. Class downloading

20 Installing Security Manager if (System.getSecurityManager() == null) { System.setSecurityManager(new SecurityManager()); } codebase = Where classes are network accessible java -Djava.rmi.server.codebase=" " -Djava.security.policy= java.policy grant { permission java.security.allpermission; }; policy file

21 Account example LAB2

22 Shared whiteboard LAB3