Prentice Hall and Sun Microsystems. Personal use only; do not redistribute.

160

Chapter 7 Generating the Server Response: HTTP Response Headers

Listing 7.3  PrimeList.java 

package coreservlets;

import java.util.*;

import java.math.BigInteger;

/** Creates a Vector of large prime numbers, usually in

 *  a low priority background thread. Provides a few small

 *  thread safe access methods.

*/

public class PrimeList implements Runnable {

  private Vector primesFound;

  private int numPrimes, numDigits;

  /** Finds numPrimes prime numbers, each of which are

   *  numDigits long or longer. You can set it to only

   *  return when done, or have it return immediately,

   *  and you can later poll it to see how far it

   *  has gotten.

   */

  public PrimeList(int numPrimes, int numDigits,

                   boolean runInBackground) {

    // Using Vector instead of ArrayList

    // to support JDK 1.1 servlet engines

    primesFound = new Vector(numPrimes);

    this.numPrimes = numPrimes;

    this.numDigits = numDigits;

    if (runInBackground) {

      Thread t = new Thread(this);

      // Use low priority so you don't slow down server.

      t.setPriority(Thread.MIN_PRIORITY);

      t.start();

    } else {

      run();

    }

  }

  public void run() {

    BigInteger start = Primes.random(numDigits);

    for(int i=0; i