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some utility class for java develop
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package com.star.id;

import com.star.string.HexUtil;

import java.util.Arrays;
import java.util.UUID;

/**
 * 用来替代jdk的uuid
 *
 * @author rolfl
 */
public final class NessUUID {

    /**
     * 不知道派啥用处,是不是uuid中的连接符
     */
    private static final int DASH = -1;
    /**
     * 不知道派什么用处,就看到用来填充lookup
     */
    private static final int ERROR = -2;

    /**
     * lookup is an array indexed by the **char**, and it has valid values set
     * with the decimal value of the hex char.
     */
    private static final long[] LOOKUP = buildLookup();

    /**
     * recode is 2-byte arrays representing the hex representation of every byte
     * value (all 256)
     */
    private static final char[][] RECODE = buildByteBlocks();

    private NessUUID() {
    }

    private static long[] buildLookup() {
        long[] lookup = new long[128];
        Arrays.fill(lookup, ERROR);
        lookup['0'] = 0;
        lookup['1'] = 1;
        lookup['2'] = 2;
        lookup['3'] = 3;
        lookup['4'] = 4;
        lookup['5'] = 5;
        lookup['6'] = 6;
        lookup['7'] = 7;
        lookup['8'] = 8;
        lookup['9'] = 9;
        lookup['a'] = 10;
        lookup['b'] = 11;
        lookup['c'] = 12;
        lookup['d'] = 13;
        lookup['e'] = 14;
        lookup['f'] = 15;
        lookup['A'] = 10;
        lookup['B'] = 11;
        lookup['C'] = 12;
        lookup['D'] = 13;
        lookup['E'] = 14;
        lookup['F'] = 15;
        lookup['-'] = DASH;
        return lookup;
    }

    private static char[][] buildByteBlocks() {
        final char[][] ret = new char[256][];
        for (int i = 0; i < ret.length; i++) {
            ret[i] = HexUtil.encodeToString(new byte[]{(byte) i}).toCharArray();
        }
        return ret;
    }

    /**
     * 取代jdk中uuid的对应方法
     *
     * @param str uuid字符串
     * @return uuid
     */
    public static UUID fromString(final String str) {
        final int len = str.length();
        if (len != 36) {
            throw new IllegalArgumentException("Invalid UUID string (expected to be 36 characters long)");
        }
        final long[] vals = new long[2];
        int shift = 60;
        int index = 0;
        for (int i = 0; i < len; i++) {
            final int c = str.charAt(i);
            if (c >= LOOKUP.length || LOOKUP[c] == ERROR) {
                throw new IllegalArgumentException("Invalid UUID string (unexpected '" + str.charAt(i)
                        + "' at position " + i + " -> " + str + " )");
            }

            if (LOOKUP[c] == DASH) {
                if ((i - 8) % 5 != 0) {
                    throw new IllegalArgumentException(
                            "Invalid UUID string (unexpected '-' at position " + i + " -> " + str + " )");
                }
                continue;
            }
            vals[index] |= LOOKUP[c] << shift;
            shift -= 4;
            if (shift < 0) {
                shift = 60;
                index++;
            }
        }
        return new UUID(vals[0], vals[1]);
    }

    /**
     * 取代jdk中uuid的对应方法
     *
     * @param uuid uuid
     * @return 字符串
     */
    public static String toString(final UUID uuid) {
        long msb = uuid.getMostSignificantBits();
        long lsb = uuid.getLeastSignificantBits();
        char[] uuidChars = new char[36];
        int cursor = uuidChars.length;
        while (cursor > 24) {
            cursor -= 2;
            System.arraycopy(RECODE[(int) (lsb & 0xff)], 0, uuidChars, cursor, 2);
            lsb >>>= 8;
        }
        uuidChars[--cursor] = '-';
        while (cursor > 19) {
            cursor -= 2;
            System.arraycopy(RECODE[(int) (lsb & 0xff)], 0, uuidChars, cursor, 2);
            lsb >>>= 8;
        }
        uuidChars[--cursor] = '-';
        while (cursor > 14) {
            cursor -= 2;
            System.arraycopy(RECODE[(int) (msb & 0xff)], 0, uuidChars, cursor, 2);
            msb >>>= 8;
        }
        uuidChars[--cursor] = '-';
        while (cursor > 9) {
            cursor -= 2;
            System.arraycopy(RECODE[(int) (msb & 0xff)], 0, uuidChars, cursor, 2);
            msb >>>= 8;
        }
        uuidChars[--cursor] = '-';
        while (cursor > 0) {
            cursor -= 2;
            System.arraycopy(RECODE[(int) (msb & 0xff)], 0, uuidChars, cursor, 2);
            msb >>>= 8;
        }
        return new String(uuidChars);
    }

    /**
     * 方便使用
     *
     * @return uuid字符串
     */
    public static String getId() {
        return toString(UUID.randomUUID());
    }
}