Example: RMI Program

1. Example: RMI Program How to write it

2. Program an ATM Machine • Allow the client to withdraw, deposit, transfer money to or from their account • Also allow to obtain the current balance • Some other stuff • ATM machine is the client • Bank with Account is the server

3. Write the code • Write the Remote Interface, call it Account • Write the implementation: AccountImpl • Write the server: RegAccount • Write the client: AccountImpl • Stubs and skeletons will be generated

4. Account.java

5. Remarks • Note that Account extends Remote • Every remote method in the interface throws a RemoteException • This interface is present on the server and on the client

6. AccountImpl.java

7. AccountImpl.java (ctd)

8. Remarks • Since this class is remote it must implement the UnicastRemote interface • The concrete methods from the remote interface all must throw a RemoteException • The rest is just POJ (Plain old Java)

9. Define the Server • Make an instance whose methods will be called by the client • Register this object with the registry • Note that it contains the main{} that defines the server • No remote exceptions here

10. RegAccount.java

11. Write the Client:AccountClient.java • Need a Security Manager (later) • Get a stub from the server by Naming.lookup() • Make the remote calls--here getName() and getBalance() • The URL parameter to the lookup routine returns the remote object it references • main(){} here is the client.

12. AccountClient.java

13. Running the Example ATM • Compile the java files: javac Account*.java • Create stub from AccountImpl: rmic AccountImpl • Start the registry: rmiregistry • Start the server: java RegAccount • Start the client: java AccountClient

14. What is Missing • A Security Manager • A Security Policy • A Codebase • Compile and Execution commands that incorporate these • An appropriate deployment strategy

15. Security Manager • If your application only runs locally (sandbox) then there is no need for security • But RMI is designed to run on networks and the Internet • Hence the need for security • The Security Manager is a Java class that checks whether certain operations are permitted • Is available under java.lang.SecurityManager

16. Security Manager (ctd) • Checks permissions according to a security policy • Infractions of permissions cause a SecurityException • Set up by issuing: System.setSecurityManager (new RMISecurityManager()); • Enclose critical code in try block

17. Permissions • Set by a security policy as written by the programmer • For purposes of testing a blanket granting of permissions can be issued: permission java.security.AllPermission; • Then after deploying be a bit more restrictive: grant{ permission java.net.SocketPermission “*:1024-65535”, “connect, accept, resolve”; permission java.net.SocketPermission “*:80”, “connect”; };

18. Codebase • When starting the server indicate the download directory by means of a codebase property: For example java -D ... - Djava.rmi.server.codebase=http://localhost/download/ xxxServ This represents the URL location from which the stubs can be downloaded Note the final slash “/” on the URL

19. Running the Client • Need to include security with -D • Start the Client: • java -Dsecurity.policy=sec.policy xxxClient • sec.policy needs a path • Do this for both server and client