RMI Example – Numerical Integration, a more realistic RMI example that sends an evaluatable object (function) from a client to a server for numerical integration.

Integral.java  Performs actual numerical integration of the function (evaluatable object).

/** A class to calculate summations and numeric integrals. The
 *  integral is calculated according to the midpoint rule.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class Integral {
  /** Returns the sum of f(x) from x=start to x=stop, where the
   *  function f is defined by the evaluate method of the
   *  Evaluatable object.
   */

  public static double sum(double start, double stop,
                           double stepSize,
                           Evaluatable evalObj) {
    double sum = 0.0, current = start;
    while (current <= stop) {
      sum += evalObj.evaluate(current);
      current += stepSize;
    }
    return(sum);
  }

  /** Returns an approximation of the integral of f(x) from
   *  start to stop, using the midpoint rule. The function f is
   *  defined by the evaluate method of the Evaluatable object.
   */

  public static double integrate(double start, double stop,
                                 int numSteps,
                                 Evaluatable evalObj) {
    double stepSize = (stop - start) / (double)numSteps;
    start = start + stepSize / 2.0;
    return(stepSize * sum(start, stop, stepSize, evalObj));
  }
}



Evaluatable.java  An interface for evaluating functions. Requires the Evaluatable  object to implement the evaluate method. 

/** An interface for evaluating functions y = f(x) at a specific
 *  value. Both x and y are double-precision floating-point
 *  numbers.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public interface Evaluatable {
  public double evaluate(double value);
}


RemoteIntegral.java  Establishes the methods in the remote object available to the client. 

import java.rmi.*;

/** Interface for remote numeric integration object.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public interface RemoteIntegral extends Remote {

  public double sum(double start, double stop, double stepSize,
                    Evaluatable evalObj)
    throws RemoteException;

  public double integrate(double start, double stop,
                          int numSteps, Evaluatable evalObj)
    throws RemoteException;
}


RemoteIntegralClient.java  The client that sends an Evaluatable object to the remote server for integration. 

import java.rmi.*;
import java.net.*;
import java.io.*;

/** This class calculates a variety of numerical integration
 *  values, printing the results of successively more accurate
 *  approximations. The actual computation is performed on a
 *  remote machine whose hostname is specified as a command-
 *  line argument.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemoteIntegralClient {
  public static void main(String[] args) {
    try {
      String host = (args.length > 0) ? args[0] : "localhost";
      RemoteIntegral remoteIntegral =
        (RemoteIntegral)Naming.lookup("rmi://" + host +
                                      "/RemoteIntegral");
      for(int steps=10; steps<=10000; steps*=10) {
        System.out.println
          ("Approximated with " + steps + " steps:" +
           "\n  Integral from 0 to pi of sin(x)=" +
           remoteIntegral.integrate(0.0, Math.PI,
                                    steps, new Sin()) +
           "\n  Integral from pi/2 to pi of cos(x)=" +
           remoteIntegral.integrate(Math.PI/2.0, Math.PI,
                                    steps, new Cos()) +
           "\n  Integral from 0 to 5 of x^2=" +
           remoteIntegral.integrate(0.0, 5.0, steps,
                                    new Quadratic()));
      }
      System.out.println
        ("`Correct' answer using Math library:" +
         "\n  Integral from 0 to pi of sin(x)=" +
         (-Math.cos(Math.PI) - -Math.cos(0.0)) +
         "\n  Integral from pi/2 to pi of cos(x)=" +
         (Math.sin(Math.PI) - Math.sin(Math.PI/2.0)) +
         "\n  Integral from 0 to 5 of x^2=" +
         (Math.pow(5.0, 3.0) / 3.0));
    } catch(RemoteException re) {
      System.out.println("RemoteException: " + re);
    } catch(NotBoundException nbe) {
      System.out.println("NotBoundException: " + nbe);
    } catch(MalformedURLException mfe) {
      System.out.println("MalformedURLException: " + mfe);
    }
  }
}


Sin.java  Evaluatable version of sin(x).
import java.io.Serializable;

/** An evaluatable version of sin(x).
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

class Sin implements Evaluatable, Serializable {
  public double evaluate(double val) {
    return(Math.sin(val));
  }

  public String toString() {
    return("Sin");
  }
}

Cos.java  Evaluatable version of cos(x). 

import java.io.Serializable;

/** An evaluatable version of cos(x).
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

class Cos implements Evaluatable, Serializable {
  public double evaluate(double val) {
    return(Math.cos(val));
  }

  public String toString() {
    return("Cosine");
  }
}


Quadratic.java  Evaluatable version of x2. 


import java.io.Serializable;

/** An evaluatable version of x^2.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

class Quadratic implements Evaluatable, Serializable {
  public double evaluate(double val) {
    return(val * val);
  }

  public String toString() {
    return("Quadratic");
  }
}

RemoteIntegralImpl.java  The remote object which provides a concrete implementation of the RemoteIntegral interface. 

import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

/** The actual implementation of the RemoteIntegral interface.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemoteIntegralImpl extends UnicastRemoteObject
                                implements RemoteIntegral {

  /** Constructor must throw RemoteException. */

  public RemoteIntegralImpl() throws RemoteException {}

  /** Returns the sum of f(x) from x=start to x=stop, where the
   *  function f is defined by the evaluate method of the
   *  Evaluatable object.
   */

  public double sum(double start, double stop, double stepSize,
                    Evaluatable evalObj) {
    return(Integral.sum(start, stop, stepSize, evalObj));
  }

  /** Returns an approximation of the integral of f(x) from
   *  start to stop, using the midpoint rule. The function f is
   *  defined by the evaluate method of the Evaluatable object.
   * @see #sum
   */

  public double integrate(double start, double stop, int numSteps,
                          Evaluatable evalObj) {
    return(Integral.integrate(start, stop, numSteps, evalObj));
  }
}



RemoteIntegralServer.java  Creates an instance of RemoteIntegralImpl on the remote server and binds the object in the registry for lookup by the client. 

import java.rmi.*;
import java.net.*;

/** Creates a RemoteIntegralImpl object and registers it under
 *  the name 'RemoteIntegral' so that remote clients can connect
 *  to it for numeric integration results. The idea is to place
 *  this server on a workstation with very fast floating-point
 *  capabilities, while slower interfaces can run on smaller
 *  computers but still use the integration routines.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemoteIntegralServer {
  public static void main(String[] args) {
    try {
      RemoteIntegralImpl integral =  new RemoteIntegralImpl();
      Naming.rebind("rmi:///RemoteIntegral", integral);
    } catch(RemoteException re) {
      System.out.println("RemoteException: " + re);
    } catch(MalformedURLException mfe) {
      System.out.println("MalformedURLException: " + mfe);
    }
  }
}


RemoteIntegralClient2.java  An enterprise version of the client that imposes a security manager to support the Java 2 RMI 1.2 stub protocol. 

import java.rmi.*;
import java.net.*;
import java.io.*;

/** This class is a Java 2 version of RemoteIntegralClient
 *  that imposes a SecurityManager to allow the client to
 *  connect to a remote machine for loading stub files and
 *  performing numerical integration through a remote
 *  object.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemoteIntegralClient2 {
  public static void main(String[] args) {
    try {
      System.setSecurityManager(new RMISecurityManager());
      String host =
        (args.length > 0) ? args[0] : "localhost";
      RemoteIntegral remoteIntegral =
        (RemoteIntegral)Naming.lookup("rmi://" + host +
                                      "/RemoteIntegral");
      for(int steps=10; steps<=10000; steps*=10) {
        System.out.println
          ("Approximated with " + steps + " steps:" +
           "\n  Integral from 0 to pi of sin(x)=" +
           remoteIntegral.integrate(0.0, Math.PI,
                                    steps, new Sin()) +
           "\n  Integral from pi/2 to pi of cos(x)=" +
           remoteIntegral.integrate(Math.PI/2.0, Math.PI,
                                    steps, new Cos()) +
           "\n  Integral from 0 to 5 of x^2=" +
           remoteIntegral.integrate(0.0, 5.0, steps,
                                    new Quadratic()));
      }
      System.out.println
        ("`Correct' answer using Math library:" +
         "\n  Integral from 0 to pi of sin(x)=" +
         (-Math.cos(Math.PI) - -Math.cos(0.0)) +
         "\n  Integral from pi/2 to pi of cos(x)=" +
         (Math.sin(Math.PI) - Math.sin(Math.PI/2.0)) +
         "\n  Integral from 0 to 5 of x^2=" +
         (Math.pow(5.0, 3.0) / 3.0));
    } catch(RemoteException re) {
      System.out.println("RemoteException: " + re);
    } catch(NotBoundException nbe) {
      System.out.println("NotBoundException: " + nbe);
    } catch(MalformedURLException mfe) {
      System.out.println("MalformedURLException: " + mfe);
    }
  }
}

rmiclient.policy  Policy file for the client. Grants permissions for the client to connect to the RMI server and Web server. 

//  Taken from Core Web Programming from
//  Prentice Hall and Sun Microsystems Press,
//  .
//  © 2001 Marty Hall and Larry Brown;
//  may be freely used or adapted.

grant {
  // rmihost - RMI registry and the server
  // webhost - HTTP server for stub classes
  permission java.net.SocketPermission 
    "rmihost:1024-65535", "connect";
  permission java.net.SocketPermission 
    "webhost:80", "connect";
};