得到任意長度的隨機字符串

創建一個實體類，需要的時候直接調取即可

package com.fh.util;

import java.util.Random;

public class RandomUtil {
	
	 public static final String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
	 public static final String LETTERCHAR = "abcdefghijkllmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
	 public static final String NUMBERCHAR = "0123456789";

	 /**
	  * 返回一個定長的隨機字符串(只包含大小寫字母、數字)
	  *
	  * @param length
	  *            隨機字符串長度
	  * @return 隨機字符串
	  */
	 public static String generateString(int length) {
	  StringBuffer sb = new StringBuffer();
	  Random random = new Random();
	  for (int i = 0; i < length; i++) {
	   sb.append(ALLCHAR.charAt(random.nextInt(ALLCHAR.length())));
	  }
	  return sb.toString();
	 }
	 /**
	  * 返回一個定長的數字串
	  *
	  * @param length
	  *            隨機字符串長度
	  * @return 隨機字符串
	  */
	 public static String generateNumber(int length) {
	  StringBuffer sb = new StringBuffer();
	  Random random = new Random();
	  for (int i = 0; i < length; i++) {
	   sb.append(NUMBERCHAR.charAt(random.nextInt(NUMBERCHAR.length())));
	  }
	  return sb.toString();
	 }

	 /**
	  * 返回一個定長的隨機純字母字符串(只包含大小寫字母)
	  *
	  * @param length
	  *            隨機字符串長度
	  * @return 隨機字符串
	  */
	 public static String generateMixString(int length) {
	  StringBuffer sb = new StringBuffer();
	  Random random = new Random();
	  for (int i = 0; i < length; i++) {
	   sb.append(ALLCHAR.charAt(random.nextInt(LETTERCHAR.length())));
	  }
	  return sb.toString();
	 }

	 /**
	  * 返回一個定長的隨機純大寫字母字符串(只包含大小寫字母)
	  *
	  * @param length
	  *            隨機字符串長度
	  * @return 隨機字符串
	  */
	 public static String generateLowerString(int length) {
	  return generateMixString(length).toLowerCase();
	 }

	 /**
	  * 返回一個定長的隨機純小寫字母字符串(只包含大小寫字母)
	  *
	  * @param length
	  *            隨機字符串長度
	  * @return 隨機字符串
	  */
	 public static String generateUpperString(int length) {
	  return generateMixString(length).toUpperCase();
	 }

	 /**
	  * 生成一個定長的純0字符串
	  *
	  * @param length
	  *            字符串長度
	  * @return 純0字符串
	  */
	 public static String generateZeroString(int length) {
	  StringBuffer sb = new StringBuffer();
	  for (int i = 0; i < length; i++) {
	   sb.append('0');
	  }
	  return sb.toString();
	 }

	 /**
	  * 根據數字生成一個定長的字符串，長度不夠前面補0
	  *
	  * @param num
	  *            數字
	  * @param fixdlenth
	  *            字符串長度
	  * @return 定長的字符串
	  */
	 public static String toFixdLengthString(long num, int fixdlenth) {
	  StringBuffer sb = new StringBuffer();
	  String strNum = String.valueOf(num);
	  if (fixdlenth - strNum.length() >= 0) {
	   sb.append(generateZeroString(fixdlenth - strNum.length()));
	  } else {
	   throw new RuntimeException("將數字" + num + "轉化爲長度爲" + fixdlenth
	     + "的字符串發生異常！");
	  }
	  sb.append(strNum);
	  return sb.toString();
	 }

	 /**
	  * 每次生成的len位數都不相同
	  *
	  * @param param
	  * @return 定長的數字
	  */
	 public static int getNotSimple(int[] param, int len) {
	  Random rand = new Random();
	  for (int i = param.length; i > 1; i--) {
	   int index = rand.nextInt(i);
	   int tmp = param[index];
	   param[index] = param[i - 1];
	   param[i - 1] = tmp;
	  }
	  int result = 0;
	  for (int i = 0; i < len; i++) {
	   result = result * 10 + param[i];
	  }
	  return result;
	 }

	 public static void main(String[] args) {
	  System.out.println("返回一個定長的隨機字符串(只包含大小寫字母、數字):" + generateString(10));
	  System.out
	    .println("返回一個定長的隨機純字母字符串(只包含大小寫字母):" + generateMixString(10));
	  System.out.println("返回一個定長的隨機純大寫字母字符串(只包含大小寫字母):"
	    + generateLowerString(10));
	  System.out.println("返回一個定長的隨機純小寫字母字符串(只包含大小寫字母):"
	    + generateUpperString(10));
	  System.out.println("生成一個定長的純0字符串:" + generateZeroString(10));
	  System.out.println("根據數字生成一個定長的字符串，長度不夠前面補0:"
	    + toFixdLengthString(123, 10));
	  int[] in = { 1, 2, 3, 4, 5, 6, 7 };
	  System.out.println("每次生成的len位數都不相同:" + getNotSimple(in, 3));
	 }
}