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 private static Random strGen = new Random();;
 private static Random numGen = new Random();;
 private static char[] numbersAndLetters = ("0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();;
 private static char[] numbers = ("0123456789").toCharArray();;
 /** * 产生随机字符串 * */
 public static final String randomString(int length) {
  if (length < 1) {
   return null;
  }
  char[] randBuffer = new char[length];
  for (int i = 0; i < randBuffer.length; i++) {
   randBuffer[i] = numbersAndLetters[strGen.nextInt(61)];
  }
  return new String(randBuffer);
 }
 
 /** * 产生随机数值字符串 * */
 public static final String randomNumStr(int length) {
  if (length < 1) {
   return null;
  }
  char[] randBuffer = new char[length];
  for (int i = 0; i < randBuffer.length; i++) {
   randBuffer[i] = numbers[numGen.nextInt(9)];
  }
  return new String(randBuffer);
 }