simpleidgenerator.java

来自「100多M的J2EE培训内容」· Java 代码 · 共 41 行

package com.borland.training.meetings.entities;

import java.security.SecureRandom;

// This class implements a simple primary key generator.
// A generated primary key is a concatenation of the current time in milliseconds
// and a random number.

public class SimpleIdGenerator implements IdGenerator {

  private static SimpleIdGenerator instance = null;
  private SecureRandom secureRandom;

  private SimpleIdGenerator() {
    try {
      secureRandom = SecureRandom.getInstance("SHA1PRNG");
    }
    catch (java.security.NoSuchAlgorithmException e) {
      System.err.println("PRNG algorithm not available");
    }
  }

  public static SimpleIdGenerator getInstance() {
    if(instance == null) {
      instance = new SimpleIdGenerator();
    }
    return instance;
  }

  public long generateId() {
    int random = secureRandom.nextInt();
    long timeNow = System.currentTimeMillis();
    int timeLow = (int) timeNow & 0xFFFFFFFF;
    if(timeLow < 0) timeLow = timeLow * -1;
    long highId = random;
    highId = highId << 32;
    long lowId = timeLow;
    long id = lowId | highId;
    return id;
  }
}