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;  
    }  

    public static void main(String[] args) {  
        System.out.println("返回一个定长的随机字符串(只包含大小写字母、数字):" + generateString(10));  
        System.out  
                .println("返回一个定长的随机纯字母字符串(只包含大小写字母):" + generateMixString(10));  
        System.out.println("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):"  
                + generateLowerString(10));  
        System.out.println("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):"  
                + generateUpperString(10));  
        System.out.println("生成一个定长的纯0字符串:" + generateZeroString(10));  
        System.out.println("根据数字生成一个定长的字符串，长度不够前面补0:"  
                + toFixdLengthString(123, 10));  
        int[] in = { 1, 2, 3, 4, 5, 6, 7 };  
        System.out.println("每次生成的len位数都不相同:" + getNotSimple(in, 3));  
    }  
}