What is RMI

1
RMI

• What is RMI
• What is needed
• Using Sun Tools
• Computer Information Systems Department
• California State Polytechnic University, Pomona

2
What is RMI

• RMI (Remote Method Invocation) is a way to enable
  a Java method to send messages that are not on
  their own machine.
• The advantages over Servlets is that access to a
  remote object is very simple.
• Even the remotes objects accessors are available
• The disadvantage over Servlets is that Servlets
  are very popular as they work directly with web
  pages

3
What is RMI

• There are two parts to an RMI system
• One is the client and the other is the service
• The server can be on any system that has a static
  address and has available the latest JDK which is
  available free from Sun Corporation

4
What is needed

• A common interface for both the client and the
  server (called a service in RMI)
• This interface extends the class Remote in the
  java rmi package
• It specifies all the behavior that must be
  implemented

5
What is needed

• For exampleimport java.rmi.Remote
• import java.rmi.RemoteException
• public interface AdderService extends Remote
• public double add(double a, double b)
  throws RemoteException

6
What is needed

• Then a class is defined that implements that
  interface for the server
• This class must have a main method that
  instantiates it and then binds it to the RMI
  service
• This class name must be appended with the
  syllable Impl
• For example AdderServiceImpl

7
What is needed

• For example in the server classpublic static
  void main (java.lang.String args) throws
  Exception
• // Initialize AdderService service new
  AdderServiceImpl()
• String serverObjectName
  "rmi//localhost/AdderService"
• // Bind to registry
• Naming.rebind (serverObjectName, service)

8
What is needed

• Then a class is generated using a Sun tool that
  implements that interface for the client
• Note we said generated it is not written by a
  programmer
• This new class is called a stub
• For example AdderServiceImpl_Stub

9
What is needed

• This class is instantiated in any place the
  programmer wishes to do so
• All it needs is the host address where the
  service resides

10
What is needed

• For examplepublic double addRemote (double a,
  double b)
• double sum 0.0
• String remoteName "rmi//" server
  "/AdderService"
• AdderService adderService
  (AdderService) Naming.lookup(remoteName)
• sum adderService.add(a, b)
• return sum

11
What is needed

• Note a try catch needs to be added to the method
  described
• Also the object needs to have the server (host)
  name
• The name should have a value like localhost or
  134.71.19.250
• A common technique is to provide the host name as
  a parameter to main

12
Using Sun Tools

• All the tools needed are provided free by Sun
  Corporation
• Note that Eclipse does not have RMI support
• The the applications required are
• rmiregistry turns on the RMI system
• rmic generates the stub from the class
  fileAdderServiceImpl_Stub from
  AdderServiceImpl

13
Summary

• RMI is a practical way to talk to a server
• It is an alternative Servlets
• Debugging aids are not available
• However, you instructor has encountered very few
  problems getting them to work
• The most practical application is interaction to
  a database
• Eclipse does not generate the stub and skeleton
  files

14
Thank You

• RMI is another Alternative to Server Side
  ProgrammingProfessor Robert Stumpf
• email rvstumpf_at_csupomona.edu url
  www.csupomona.edu/rvstumpf