uuidgenerator.java

来自「OpenJMS是一个开源的Java Message Service API 1.」· Java 代码 · 共 899 行 · 第 1/3 页

     * @return An identifier
     */
    public static String create() {
        return String.valueOf(createTimeUUIDChars());
    }


    /**
     * Creates and returns a new prefixed identifier.
     * <p>
     * This method is equivalent to <code>prefix + create()</code>.
     *
     * @param prefix The prefix to use
     * @return A prefixed identifier
     */
    public static String create(String prefix) {
        StringBuffer buffer;

        if (prefix == null) {
            throw new IllegalArgumentException("Argument 'prefix' is null");
        }
        buffer = new StringBuffer(MAXIMUM_LENGTH - MAXIMUM_PREFIX + prefix.length());
        buffer.append(prefix);
        buffer.append(createTimeUUIDChars());
        return buffer.toString();
    }


    /**
     * Creates and returns a new identifier.
     *
     * @return An identifier
     */
    public static byte[] createBinary() {
        return createTimeUUIDBytes();
    }


    /**
     * Converts a prefixed identifier into a byte array. An exception
     * is thrown if the identifier does not match the excepted textual
     * encoding.
     * <p>
     * The format for the identifier is <code>prefix{nn|-}*</code>:
     * a prefix followed by a sequence of bytes, optionally separated
     * by hyphens. Each byte is encoded as a pair of hexadecimal digits.
     *
     * @param prefix The identifier prefix
     * @param identifier The prefixed identifier
     * @return The identifier as an array of bytes
     * @throws InvalidIDException The identifier does not begin with
     * the prefix, or does not consist of a sequence of hexadecimal
     * digit pairs, optionally separated by hyphens
     */
    public static byte[] toBytes(String prefix, String identifier)
        throws InvalidIDException {

        int index;
        char digit;
        byte nibble;
        byte[] bytes;
        byte[] newBytes;

        if (identifier == null) {
            throw new IllegalArgumentException("Argument identifier is null");
        }
        if (prefix == null) {
            throw new IllegalArgumentException("Argument prefix is null");
        }
        if (!identifier.startsWith(prefix)) {
            throw new InvalidIDException(
                "Invalid identifier: expected prefix " + prefix
                + "in identifier " + identifier);
        }

        index = 0;
        bytes = new byte[(identifier.length() - prefix.length()) / 2];
        for (int i = prefix.length(); i < identifier.length(); ++i) {
            digit = identifier.charAt(i);
            if (digit == '-') {
                continue;
            }
            if (digit >= '0' && digit <= '9') {
                nibble = (byte) ((digit - '0') << 4);
            } else if (digit >= 'A' && digit <= 'F') {
                nibble = (byte) ((digit - ('A' - 0x0A)) << 4);
            } else if (digit >= 'a' && digit <= 'f') {
                nibble = (byte) ((digit - ('a' - 0x0A)) << 4);
            } else {
                throw new InvalidIDException(
                    "character " + String.valueOf(digit)
                    + " encountered, expected hexadecimal digit in identifier "
                    + identifier);
            }
            ++i;
            if (i == identifier.length()) {
                throw new InvalidIDException(
                    "Invalid identifier: odd number of hexadecimal digits in "
                    + "identifier " + identifier);
            }
            digit = identifier.charAt(i);
            if (digit >= '0' && digit <= '9') {
                nibble = (byte) (nibble | (digit - '0'));
            } else if (digit >= 'A' && digit <= 'F') {
                nibble = (byte) (nibble | (digit - ('A' - 0x0A)));
            } else if (digit >= 'a' && digit <= 'f') {
                nibble = (byte) (nibble | (digit - ('a' - 0x0A)));
            } else {
                throw new InvalidIDException(
                    "character " + String.valueOf(digit)
                    + " encountered, expected hexadecimal digit in identifier "
                    + identifier);
            }
            bytes[index] = nibble;
            ++index;
        }
        if (index == bytes.length) {
            return bytes;
        }
        newBytes = new byte[index];
        while (index-- > 0) {
            newBytes[index] = bytes[index];
        }
        return newBytes;
    }


    /**
     * Converts an identifier into a byte array. An exception is
     * thrown if the identifier does not match the excepted textual
     * encoding.
     * <p>
     * The format for the identifier is <code>{nn|-}*</code>:
     * a sequence of bytes, optionally separated by hyphens.
     * Each byte is encoded as a pair of hexadecimal digits.
     *
     * @param identifier The identifier
     * @return The identifier as an array of bytes
     * @throws InvalidIDException The identifier does not consist
     * of a sequence of hexadecimal digit pairs, optionally separated
     * by hyphens
     */
    public static byte[] toBytes(String identifier) throws InvalidIDException {
        int index;
        char digit;
        byte nibble;
        byte[] bytes;
        byte[] newBytes;

        if (identifier == null) {
            throw new IllegalArgumentException("Argument identifier is null");
        }
        index = 0;
        bytes = new byte[identifier.length() / 2];
        for (int i = 0; i < identifier.length(); ++i) {
            digit = identifier.charAt(i);
            if (digit == '-')
                continue;
            if (digit >= '0' && digit <= '9')
                nibble = (byte) ((digit - '0') << 4);
            else if (digit >= 'A' && digit <= 'F')
                nibble = (byte) ((digit - ('A' - 0x0A)) << 4);
            else if (digit >= 'a' && digit <= 'f')
                nibble = (byte) ((digit - ('a' - 0x0A)) << 4);
            else {
                throw new InvalidIDException(
                    "character " + String.valueOf(digit)
                    + " encountered, expected hexadecimal digit in identifier "
                    + identifier);
            }
            ++i;
            if (i == identifier.length()) {
                throw new InvalidIDException(
                    "Invalid identifier: odd number of hexadecimal digits in "
                    + "identifier " + identifier);
            }
            digit = identifier.charAt(i);
            if (digit >= '0' && digit <= '9')
                nibble = (byte) (nibble | (digit - '0'));
            else if (digit >= 'A' && digit <= 'F')
                nibble = (byte) (nibble | (digit - ('A' - 0x0A)));
            else if (digit >= 'a' && digit <= 'f')
                nibble = (byte) (nibble | (digit - ('a' - 0x0A)));
            else {
                throw new InvalidIDException(
                    "character " + String.valueOf(digit)
                    + " encountered, expected hexadecimal digit in identifier "
                    + identifier);
            }
            bytes[index] = nibble;
            ++index;
        }
        if (index == bytes.length)
            return bytes;
        newBytes = new byte[index];
        while (index-- > 0)
            newBytes[index] = bytes[index];
        return newBytes;
    }


    /**
     * Converts a byte array into a prefixed identifier.
     * <p>
     * The format for the identifier is <code>prefix{nn|-}*</code>:
     * a prefix followed by a sequence of bytes, optionally separated
     * by hyphens. Each byte is encoded as a pair of hexadecimal digits.
     *
     * @param prefix The identifier prefix
     * @param byte An array of bytes
     * @return A string representation of the identifier
     */
    public static String fromBytes(String prefix, byte[] bytes) {
        StringBuffer buffer;

        if (prefix == null)
            throw new IllegalArgumentException("Argument prefix is null");
        if (bytes == null || bytes.length == 0)
            throw new IllegalArgumentException("Argument bytes is null or an empty array");
        buffer = new StringBuffer(prefix);
        for (int i = 0; i < bytes.length; ++i) {
            buffer.append(HEX_DIGITS[(bytes[i] & 0xF0) >> 4]);
            buffer.append(HEX_DIGITS[(bytes[i] & 0x0F)]);
        }
        return buffer.toString();
    }


    /**
     * Converts a byte array into an identifier.
     * <p>
     * The format for the identifier is <code>{nn|-}*</code>: a sequence
     * of bytes, optionally separated by hyphens. Each byte is encoded as
     * a pair of hexadecimal digits.
     *
     * @param bytes An array of bytes
     * @return A string representation of the identifier
     */
    public static String fromBytes(byte[] bytes) {
        StringBuffer buffer;

        if (bytes == null || bytes.length == 0)
            throw new IllegalArgumentException("Argument bytes is null or an empty array");
        buffer = new StringBuffer();
        for (int i = 0; i < bytes.length; ++i) {
            buffer.append(HEX_DIGITS[(bytes[i] & 0xF0) >> 4]);
            buffer.append(HEX_DIGITS[(bytes[i] & 0x0F)]);
        }
        return buffer.toString();
    }


    /**
     * Truncates an identifier so that it does not extend beyond
     * {@link #MAXIMUM_LENGTH} characters in length.
     *
     * @param identifier An identifier
     * @return An identifier trimmed to {@link #MAXIMUM_LENGTH} characters
     */
    public static String trim(String identifier) {
        if (identifier == null)
            throw new IllegalArgumentException("Argument identifier is null");
        if (identifier.length() > MAXIMUM_LENGTH)
            return identifier.substring(0, MAXIMUM_LENGTH);
        return identifier;
    }


    /**
     * Returns a time-based UUID as a character array. The UUID
     * identifier is always 36 characters long.
     *
     * @return A time-based UUID
     */
    public static char[] createTimeUUIDChars() {
        long clock;
        char[] chars;
        long nextClock;

        // Acquire lock to assure synchornized generation
        synchronized (UUID.class) {
            clock = Clock.clock();
            while (true) {
                if (clock > _lastClock) {
                    // Since we are using the clock interval for the UUID space,
                    // we must make sure the next clock provides sufficient
                    // room so UUIDs do not roll over.
                    nextClock = _lastClock + (_uuidsThisTick / 100);
                    if (clock <= nextClock)
                        clock = Clock.synchronize();
                    if (clock > nextClock) {
                        // Clock reading changed since last UUID generated,
                        // reset count of UUIDs generated with this clock.
                        _uuidsThisTick = 0;
                        _lastClock = clock;
                        // Adjust UUIDs per tick in case the clock sleep ticks
                        // have changed.
                        _uuidsPerTick = Clock.getUnsynchTicks() * 100;
                        break;
                    }