Java 生成随机数

public class RandomUtil {
 
	    public static final String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";  
	    public static final String LETTERCHAR = "abcdefghijkllmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";  
	    public static final String NUMBERCHAR = "0123456789";  
	  
	    /** 
	     * 返回一个定长的随机字符串(只包含大小写字母、数字) 
	     *  
	     * @param length 
	     *            随机字符串长度 
	     * @return 随机字符串 
	     */  
	    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();  
	    }  
	  
	    /** 
	     * 返回一个定长的随机纯字母字符串(只包含大小写字母) 
	     *  
	     * @param length 
	     *            随机字符串长度 
	     * @return 随机字符串 
	     */  
	    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();  
	    }  
	  
	    /** 
	     * 返回一个定长的随机纯大写字母字符串(只包含大小写字母) 
	     *  
	     * @param length 
	     *            随机字符串长度 
	     * @return 随机字符串 
	     */  
	    public static String generateLowerString(int length) {  
	        return generateMixString(length).toLowerCase();  
	    }  
	  
	    /** 
	     * 返回一个定长的随机纯小写字母字符串(只包含大小写字母) 
	     *  
	     * @param length 
	     *            随机字符串长度 
	     * @return 随机字符串 
	     */  
	    public static String generateUpperString(int length) {  
	        return generateMixString(length).toUpperCase();  
	    }  
	  
	    /** 
	     * 生成一个定长的纯0字符串 
	     *  
	     * @param length 
	     *            字符串长度 
	     * @return 纯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();  
	    }  
	  
	    /** 
	     * 根据数字生成一个定长的字符串，长度不够前面补0 
	     *  
	     * @param num 
	     *            数字 
	     * @param fixdlenth 
	     *            字符串长度 
	     * @return 定长的字符串 
	     */  
	    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("将数字" + num + "转化为长度为" + fixdlenth  
	                    + "的字符串发生异常！");  
	        }  
	        sb.append(strNum);  
	        return sb.toString();  
	    }  
	  
	    /** 
	     * 每次生成的len位数都不相同 
	     *  
	     * @param param 
	     * @return 定长的数字 
	     */  
	    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;  
	    }  
}