Java%20RMI%20(more)

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Java RMI (more)

• CS-328
• Internet Programming

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Remote Interface

• This really the interface for the servers methods
• Must be public
• must extend Remote
• each method in the interface must throw
  RemoteException in addition to any application
  specific exceptions

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Example
package rmi.hello public interface Hello extends
java.rmi.Remote String sayHello() throws
java.rmi.RemoteException
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Remote Object Implememtation

• Must specify the remote interfaces being
  implemented
• optionally extend a remote server
• extending UnicastRemoteObject indicates a single,
  non-replicated remote object
• define the default constructor
• must throw RemoteException
• provide an implementation for each remote method
  defined in the interface
• create and install a security manager either
  RMISecurityManager or one you have defined
• create one or more instances of remote object
• register at least one object with the RMI
  Registry

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Example
package rmi.hello import java.rmi. import
java.rmi.server.UnicastRemoteObject public class
HelloImpl extends UnicastRemoteObject implements
Hello private String name public
HelloImpl(String s) throws java.rmi.RemoteExceptio
n super() name s public
String sayHello() throws RemoteException
return Hello World public static void
main (String args)
System.setSecurityManager(new RMISecurityManager()
) try HelloImpl obj
new HelloImpl(HELLOSERVER)
Naming.rebind(HELLOSERVER,obj)
System.out.println( HelloImpl created and bound
to registry as HELLOSERVER) catch
(Exception e) System.out.println
(Exception e.toString)
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UnicastRemoteObject

• A form of a remote server
• the server cannot be started remotely, must
  already exist and the reference exists only as
  long as the process
• Uses TCP/IP ( the RMI specification is written
  for network protocol independence)
• An object stream is used to parameters and methos
  invocations between client and server
• Other types of servers will be made available as
  they are developed
• JDK 1.3 also provides Multicast

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Local Client

• look-up the remote object and get a reference to
  its local stub
• invoke one or more remote methods
• just like invoking a method on a local object

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Example
package rmi.hello import java.rmi. import
java.awt. public class HelloApplet extends
java.applet.Applet String message
public void init() try
Hello obj (Hello)Naming.lookup(//
getCodeBase().getHost()
/HELLOSERVER) message
obj.sayHello() catch (Exception e)
System.out.println(Exception
e.toString()) public void
paint(Graphics g) g.drawString(message, 25,
50)
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HTML
lthtmlgt ltheadgt lttitlegtHello Worldlt/titlegt lt/headgt lt
bodygt ltpgtThe message from the Hello Server
is ltapplet codebase../..
codermi.hello.HelloApplet
width500 height120gt lt/appletgt lt/htmlgt