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Java RMI: Project 5 - Building a Peer-to-Peer Messaging System, Study Guides, Projects, Research of Programming Languages

University of Maryland Programming Languages

Instructions for project 5 in the cmsc 433 - programming language technologies and paradigms course, focusing on java remote method invocation (rmi). Students are required to create a peer-to-peer messaging system that can connect to a well-known host, send and receive messages, and handle failed clients. The document also covers the basics of an rmi application, including interfaces, implementation, and registration.

Typology: Study Guides, Projects, Research

Pre 2010

Uploaded on 07/30/2009

koofers-user-y3l 🇺🇸

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CMSC 433 – Programming Language

Technologies and Paradigms

Spring 2003

Partial preview of the text

Download Java RMI: Project 5 - Building a Peer-to-Peer Messaging System and more Study Guides, Projects, Research Programming Languages in PDF only on Docsity!

CMSC 433 – Programming Language

Technologies and Paradigms

Spring 2003

More on Java RMI

April 22, 2003

Project 5

Your code needs to be able to
- Connect to well known host and ask to peer
- Send PeerWithMe messages to get more peers
- Accept peerWithMe calls (respect maxPeers)
- Send messages
  - Discard duplicates
  - Forward text messages (not back to source)
- Respond to PeerWithMe messages
- Handle failed client

What You Don’t Need to Do

Don’t worry about handling slow clients
- You’ll need to do this for project 6

A Typical RMI Application

Client and Server run on different machines
Remote Object(s) registered by Server
Remote Object(s) looked up by Client
Code transferred point of use
- Using code base, usually via HTTP
RMI carries out operations on Remote

Objects

Example Compute Server Application

Example from Java RMI tutorial
- http://java.sun.com/docs/books/tutorial/rmi/
Goal
- Execute object methods on a remote machine
- Often because local resources aren’t sufficient

Compute Interface

public interface Compute extends Remote { RemoteException;^ Object^ executeTask(Task^ t)^ throws }

Compute extends Remote
- Any class implementing Compute can be used remotely
  - Its remote methods can be called from any JVM
  - Its implementation resides on the JVM in which it was created
executeTask() is a remote method
- It may throw RemoteException

Task Interface

public interface Task extends Serializable { Object execute(); }

Task implementations implement Serializable, rather than Remote - Why?
execute() method returns an Object
- Client must downcast result
- This method not required to throw RemoteException

Implementing Compute Engine

Our implementation of compute interface

will be called ComputeEngine

In general, the implementer of a remote

interface should at least

Declare the remote interfaces being implemented
Define the constructor for the remote object
Implement each remote method in the remote interfaces

Further Requirements for Servers

Server creates and installs remote objects
- Often done in method of remote object
  - but can be done anywhere
Setup procedure should
1. Create and install a security manager
  - if you’ll be downloading code
2. Create one or more instances of remote object
3. Register remote object(s) with the RMI registry

Declare the Remote Interfaces

ComputeEngine class declared as
- public class ComputeEngine extends UnicastRemoteObject implements Compute
Declaration states that
- class implements Compute remote interface
- extends the class java.rmi.server.UnicastRemoteObject - Magic

Define the Constructor

public ComputeEngine() throws RemoteException { super(); // (not necessary) }

Must throw RemoteException
- Because the UnicastRemoteObject constructor does
- RemoteException can occur during construction if attempt to export object fails - For example, if communication resources are unavailable or the appropriate stub class is not found

RMI Registry

Simple remote object name service
- Allows remote clients to get reference to remote object by name
Can start the registry
- From the command line as separate process, or
- From within your server program

Add Remote Object to Registry

java.rmi.Naming provides API to registry
- Binding (or reigstering), unbinding, look-ups
ComputeEngine adds remote object to registry String name = "//host/Compute"; Naming.rebind(name, engine);

More on Registering Objects

Naming.rebind(String, Object)
- First parameter is URL-formatted java.lang.String representing location and name of remote object
- Default port number is 1099
For security reasons, can bind, unbind, or

rebind only with registry on local host

Once server has registered the remote

object, setup procedure exits

Creating a Client Program

Two separate classes make up the client in

our example

ComputePi
Pi
ComputePi obtains reference to Compute

object, creates Task object, and then request

that the task be executed

Pi implements the Task interface,

calculating Pi to some degree of precision

ComputePi

if (System.getSecurityManager() == null) { System.setSecurityManager(new RMISecurityManager()); } String name = “//” + args[0] + “/Compute”; Compute comp = (Compute) Naming.lookup(name); Pi task = new Pi(Integer.parseInt(args[1])); BigDecimal pi = (BigDecimal) comp.executeTask(task);

ComputePi

Begins by installing a security manager
Uses Naming.lookup() to look up remote

object by name in the remote host's registry

Creates new Pi object
Invokes executeTask() on Compute remote

object, which

returns a java.math.BigDecimal, so the

program downcast casts result and stores it

Program prints out the result

Pi

Calculates Pi

Compiling

Application has 4 directory trees
Server
- Application directory
  - server code written and compiled here
- Web accessible location
  - client downloads server code from here
Client
- Application directory
  - client code written and compiled here
- Web accessible location
  - server downloads client code from here

Tips for Building RMI Apps

If code for your objects will be downloaded, keep client and server code in separate directory trees - Maybe even separate machines - Otherwise hard to test, because of classpath
Use file: URLs for local testing without web
Simple HTTP server for RMI classes available
- ftp://ftp.javasoft.com/pub/jdk1.1/rmi/class- server.zip

Remote Interfaces

Everyone needs the remote interfaces
- Put in developer-accessible locations
- Put in web-accessible locations
- Everyone shares these files
  - don’t change them
Might be handy to have interfaces in jar file

Building the Server

cd ServerDevDir
javac engine/ComputeEngine.java
rmic -v1.2 -d. engine.ComputeEngine
- Notice takes a class as an argument
- (Classpath omitted from above two lines)
mkdir ServerWebDir/engine
cp engine/ComputeEngine_Stub.class ServerWebDir/engine
Stubs now web-accessible

Building the Client

cd ClientDevDir
javac client/ComputePi.java
javac -d ClientWebDir client/Pi.java
- Recall that Pi is Serializable
- So full source code (not just stub) must be availble
Serializable class now web-accessible

Java RMI: Project 5 - Building a Peer-to-Peer Messaging System, Study Guides, Projects, Research of Programming Languages

Related documents

Partial preview of the text

Download Java RMI: Project 5 - Building a Peer-to-Peer Messaging System and more Study Guides, Projects, Research Programming Languages in PDF only on Docsity!

CMSC 433 – Programming Language

Technologies and Paradigms

Spring 2003

More on Java RMI

April 22, 2003

Project 5

What You Don’t Need to Do

A Typical RMI Application

Objects

Example Compute Server Application

Compute Interface

Task Interface

Implementing Compute Engine

will be called ComputeEngine

interface should at least

Further Requirements for Servers

Declare the Remote Interfaces

Define the Constructor

RMI Registry

Add Remote Object to Registry

More on Registering Objects

rebind only with registry on local host

object, setup procedure exits

Creating a Client Program

our example

object, creates Task object, and then request

that the task be executed

calculating Pi to some degree of precision

ComputePi

ComputePi

object by name in the remote host's registry

object, which

program downcast casts result and stores it

Pi

Compiling

Tips for Building RMI Apps

Remote Interfaces

Building the Server

Building the Client