util

import java.security.SecureRandom;

public class RandomNumberUtil {

    private static char[] chars = {‘a‘,‘b‘,‘c‘,‘d‘,‘e‘,‘f‘,‘g‘,‘h‘,‘i‘,‘j‘,‘k‘,‘l‘,‘m‘,‘n‘,‘o‘,‘p‘,‘q‘,
            ‘r‘,‘s‘,‘t‘,‘u‘,‘v‘,‘w‘,‘x‘,‘y‘,‘z‘,‘0‘,‘1‘,‘2‘,‘3‘,‘4‘,‘5‘,‘6‘,‘7‘,‘8‘,‘9‘};
    private static int charLength = chars.length;
    private static RandomNumberUtil instance = new RandomNumberUtil();

    public static RandomNumberUtil getInstance() {
        return instance;
    }

    public static String generateLetterCode(int length) {
        StringBuilder sb = new StringBuilder();
        SecureRandom random;
        try {
            random = SecureRandom.getInstance("SHA1PRNG");
            int index = 0;
            for (int i = 0;i < length;i++) {
                index = Math.abs(random.nextInt()) % charLength;
                char c = chars[index];
                sb.append(c);
            }
        } catch (Exception e) {
        }
        return sb.toString();
    }
    
    
    /**
     * 
     * get random
     * 
     * @return
     */
    private String generateCheckCode(int randomBit) {
        // difine chars table of validate code
//        String chars = "0123456789";
        StringBuilder sb = new StringBuilder();
        char[] rands = new char[randomBit];
        for (int i = 0; i < randomBit; i++) {
            SecureRandom random;
            try {
                random = SecureRandom.getInstance("SHA1PRNG");
//                int rand = (int) (Math.abs(random.nextInt()) * 10);
//                rands[i] = chars.charAt(rand);
                sb.append(Math.abs(random.nextInt()) % 10);
            } catch (Exception e) {
                
            }
        }
        return sb.toString();
    }

    /**
     * get default random
     * 
     * date(yyyyMMddHHmmss) and random(4)
     * 
     * @return
     */
    public String getRandom() {
        return DateUtil.getInstance().getCurrentTime("yyyyMMddHHmmss")
                + generateCheckCode(4);
    }
    /**
     * 
     * @param randomBit
     * @return
     */
    public String getDateRandoms(int randomBit) {
        return DateUtil.getInstance().getCurrentTime("yyyyMMddHHmmss")
                + generateCheckCode(randomBit);
    }

    /**
     * get random by randomBit
     * 
     * @param randomBit
     * @return
     */
    public String getRandom(int randomBit) {
        return generateCheckCode(randomBit);
    }

    /**
     * 
     * get random by date
     * 
     * @param formatStr
     * @return
     */
    public String getRandom(String formatStr) {
        return DateUtil.getInstance().getCurrentTime(formatStr);
    }

    /**
     * 
     * get random by date and randomBit
     * 
     * @param formatStr
     * @param randomBit
     * @return
     */
    public String getRandom(String formatStr, int randomBit) {
        return DateUtil.getInstance().getCurrentTime(formatStr)
                + generateCheckCode(randomBit);
    }


    public static void main(String[] args) {

        
//        String randomLetters = RandomNumberUtil.generateLetterCode(32);
//        System.out.println(randomLetters);
//        System.out.println(randomLetters + "    " + randomLetters.length());
        System.out.println(RandomNumberUtil.generateLetterCode(50));
        System.out.println(RandomNumberUtil.getInstance().getDateRandoms(8));

    }

}