【java】性能翻倍的超短19位UUID生成工具类

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package p2p.utils;
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
public class UuidUtil {
final static char[] digits = { '0', '1', '2', '3', '4', '5', '6', '7', '8',
'9', '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', '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' };
final static Map<Character, Integer> digitMap = new HashMap<Character, Integer>();
static {
for (int i = 0; i < digits.length; i++) {
digitMap.put(digits[i], (int) i);
}
}
/**
* 支持的最大进制数
*/
public static final int MAX_RADIX = digits.length;
/**
* 支持的最小进制数
*/
public static final int MIN_RADIX = 2;
/**
* 将长整型数值转换为指定的进制数（最大支持62进制，字母数字已经用尽）
*
* @param i
* @param radix
* @return
*/
public static String toString(long i, int radix) {
if (radix < MIN_RADIX || radix > MAX_RADIX)
radix = 10;
if (radix == 10)
return Long.toString(i);
final int size = 65;
int charPos = 64;
char[] buf = new char[size];
boolean negative = (i < 0);
if (!negative) {
i = -i;
}
while (i <= -radix) {
buf[charPos--] = digits[(int) (-(i % radix))];
i = i / radix;
}
buf[charPos] = digits[(int) (-i)];
if (negative) {
buf[--charPos] = '-';
}
return new String(buf, charPos, (size - charPos));
}
static NumberFormatException forInputString(String s) {
return new NumberFormatException("For input string: \"" + s + "\"");
}
/**
* 将字符串转换为长整型数字
*
* @param s
* 数字字符串
* @param radix
* 进制数
* @return
*/
public static long toNumber(String s, int radix) {
if (s == null) {
throw new NumberFormatException("null");
}
if (radix < MIN_RADIX) {
throw new NumberFormatException("radix " + radix
+ " less than Numbers.MIN_RADIX");
}
if (radix > MAX_RADIX) {
throw new NumberFormatException("radix " + radix
+ " greater than Numbers.MAX_RADIX");
}
long result = 0;
boolean negative = false;
int i = 0, len = s.length();
long limit = -Long.MAX_VALUE;
long multmin;
Integer digit;
if (len > 0) {
char firstChar = s.charAt(0);
if (firstChar < '0') {
if (firstChar == '-') {
negative = true;
limit = Long.MIN_VALUE;
} else if (firstChar != '+')
throw forInputString(s);
if (len == 1) {
throw forInputString(s);
}
i++;
}
multmin = limit / radix;
while (i < len) {
digit = digitMap.get(s.charAt(i++));
if (digit == null) {
throw forInputString(s);
}
if (digit < 0) {
throw forInputString(s);
}
if (result < multmin) {
throw forInputString(s);
}
result *= radix;
if (result < limit + digit) {
throw forInputString(s);
}
result -= digit;
}
} else {
throw forInputString(s);
}
return negative ? result : -result;
}
/**
* 编写uuid生成工具方法
* @param val
* @param digits
* @return
*/
public static String digits(long val, int digits) {
long hi = 1L << (digits * 4);
return toString(hi | (val & (hi - 1)), MAX_RADIX)
.substring(1);
}
/**
* 以62进制（字母加数字）生成19位UUID，最短的UUID
*
* @return
*/
public static String uuid() {
UUID uuid = UUID.randomUUID();
StringBuilder sb = new StringBuilder();
sb.append(digits(uuid.getMostSignificantBits() >> 32, 8));
sb.append(digits(uuid.getMostSignificantBits() >> 16, 4));
sb.append(digits(uuid.getMostSignificantBits(), 4));
sb.append(digits(uuid.getLeastSignificantBits() >> 48, 4));
sb.append(digits(uuid.getLeastSignificantBits(), 12));
return sb.toString();
}
}

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