我想创建跨机器唯一的 9 位数字 ID。我目前正在为此使用数据库序列，但我想知道是否可以在没有数据库序列的情况下完成。这些序列将用于 X12 EDI 交易，因此它们不必永远唯一。甚至可能只在 24 小时内独一无二。
我唯一的想法：
我最大的问题是如果硬盘驱动器出现故障该怎么办。我不知道它从哪里停下来。
我所有其他的想法基本上都是重新创建一个集中的数据库序列。
有什么想法吗？
【问题讨论】：
标签： x12
以下
{XX}{dd}{HHmm}{N}
其中 {XX} 是机器编号 {dd} 是当前时间（24 小时）月份中的某天 {HHmm}，而 {N} 是序列号。
高清崩溃需要一分钟以上，因此再次从 0 开始不是问题。
您也可以将 {dd} 替换为 {ss} 几秒钟，具体取决于要求。唯一性周期与每分钟请求数。
【讨论】：
如果 HD 失败，您可以设置新的和未使用的 2 位服务器标识符，并确保该号码是唯一的（至少 24 小时）
【讨论】：
如何生成 GUID（确保唯一性），然后使用某种哈希函数将 GUID 转换为 9 位数字？
就在我的头顶上......
【讨论】：
使用变体：
md5(uniqid(rand(), true));
只是一个想法。
【讨论】：
在我最近的项目中我也遇到了这个需求，在没有任何数据库的情况下生成 N 位长序列号。
这其实是一个很好的面试题，因为有性能和软件崩溃恢复方面的考虑。 Further Reading如果有兴趣。
以下代码具有以下特点：
为每个序列加上前缀。
类似 Oracle 序列的序列缓存。
最重要的是，有恢复逻辑可以从软件崩溃中恢复序列。
附上完整的实现：
import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.lang.StringUtils;
/**
* This is a customized Sequence Generator which simulates Oracle DB Sequence Generator. However the master sequence
* is stored locally in the file as there is no access to Oracle database. The output format is "prefix" + number.
* <p>
* <u><b>Sample output:</u></b><br>
* 1. FixLengthIDSequence(null,null,15,0,99,0) will generate 15, 16, ... 99, 00<br>
* 2. FixLengthIDSequence(null,"K",1,1,99,0) will generate K01, K02, ... K99, K01<br>
* 3. FixLengthIDSequence(null,"SG",100,2,9999,100) will generate SG0100, SG0101, ... SG8057, (in case server crashes, the new init value will start from last cache value+1) SG8101, ... SG9999, SG0002<br>
*/
public final class FixLengthIDSequence {
private static String FNAME;
private static String PREFIX;
private static AtomicLong SEQ_ID;
private static long MINVALUE;
private static long MAXVALUE;
private static long CACHEVALUE;
// some internal working values.
private int iMaxLength; // max numeric length excluding prefix, for left padding zeros.
private long lNextSnapshot; // to keep track of when to update sequence value to file.
private static boolean bInit = false; // to enable ShutdownHook routine after program has properly initialized
static {
// Inspiration from http://stackoverflow.com/questions/22416826/sequence-generator-in-java-for-unique-id#35697336.
Runtime.getRuntime().addShutdownHook(new Thread(() -> {
if (bInit) { // Without this, saveToLocal may hit NullPointerException.
saveToLocal(SEQ_ID.longValue());
}
}));
}
/**
* This POJO style constructor should be initialized via Spring Singleton. Otherwise, rewrite this constructor into Singleton design pattern.
*
* @param sFilename This is the absolute file path to store the sequence number. To reset the sequence, this file needs to be removed manually.
* @param prefix The hard-coded identifier.
* @param initvalue
* @param minvalue
* @param maxvalue
* @param cache
* @throws Exception
*/
public FixLengthIDSequence(String sFilename, String prefix, long initvalue, long minvalue, long maxvalue, int cache) throws Exception {
bInit = false;
FNAME = (sFilename==null)?"C:\\Temp\\sequence.txt":sFilename;
PREFIX = (prefix==null)?"":prefix;
SEQ_ID = new AtomicLong(initvalue);
MINVALUE = minvalue;
MAXVALUE = maxvalue; iMaxLength = Long.toString(MAXVALUE).length();
CACHEVALUE = (cache <= 0)?1:cache; lNextSnapshot = roundUpNumberByMultipleValue(initvalue, cache); // Internal cache is always 1, equals no cache.
// If sequence file exists and valid, restore the saved sequence.
java.io.File f = new java.io.File(FNAME);
if (f.exists()) {
String[] saSavedSequence = loadToString().split(",");
if (saSavedSequence.length != 6) {
throw new Exception("Local Sequence file is not valid");
}
PREFIX = saSavedSequence[0];
//SEQ_ID = new AtomicLong(Long.parseLong(saSavedSequence[1])); // savedInitValue
MINVALUE = Long.parseLong(saSavedSequence[2]);
MAXVALUE = Long.parseLong(saSavedSequence[3]); iMaxLength = Long.toString(MAXVALUE).length();
CACHEVALUE = Long.parseLong(saSavedSequence[4]);
lNextSnapshot = Long.parseLong(saSavedSequence[5]);
// For sequence number recovery
// The rule to determine to continue using SEQ_ID or lNextSnapshot as subsequent sequence number:
// If savedInitValue = savedSnapshot, it was saved by ShutdownHook -> use SEQ_ID.
// Else if saveInitValue < savedSnapshot, it was saved by periodic Snapshot -> use lNextSnapshot+1.
if (saSavedSequence[1].equals(saSavedSequence[5])) {
long previousSEQ = Long.parseLong(saSavedSequence[1]);
SEQ_ID = new AtomicLong(previousSEQ);
lNextSnapshot = roundUpNumberByMultipleValue(previousSEQ,CACHEVALUE);
} else {
SEQ_ID = new AtomicLong(lNextSnapshot+1); // SEQ_ID starts fresh from lNextSnapshot+!.
lNextSnapshot = roundUpNumberByMultipleValue(SEQ_ID.longValue(),CACHEVALUE);
}
}
// Catch invalid values.
if (minvalue < 0) {
throw new Exception("MINVALUE cannot be less than 0");
}
if (maxvalue < 0) {
throw new Exception("MAXVALUE cannot be less than 0");
}
if (minvalue >= maxvalue) {
throw new Exception("MINVALUE cannot be greater than MAXVALUE");
}
if (cache >= maxvalue) {
throw new Exception("CACHE value cannot be greater than MAXVALUE");
}
// Save the next Snapshot.
saveToLocal(lNextSnapshot);
bInit = true;
}
/**
* Equivalent to Oracle Sequence nextval.
* @return String because Next Value is usually left padded with zeros, e.g. "00001".
*/
public String nextVal() {
if (SEQ_ID.longValue() > MAXVALUE) {
SEQ_ID.set(MINVALUE);
lNextSnapshot = roundUpNumberByMultipleValue(MINVALUE,CACHEVALUE);
}
if (SEQ_ID.longValue() > lNextSnapshot) {
lNextSnapshot = roundUpNumberByMultipleValue(lNextSnapshot,CACHEVALUE);
saveToLocal(lNextSnapshot);
}
return PREFIX.concat(StringUtils.leftPad(Long.toString(SEQ_ID.getAndIncrement()),iMaxLength,"0"));
}
/**
* Store sequence value into the local file. This routine is called either by Snapshot or ShutdownHook routines.<br>
* If called by Snapshot, currentCount == Snapshot.<br>
* If called by ShutdownHook, currentCount == current SEQ_ID.
* @param currentCount - This value is inserted by either Snapshot or ShutdownHook routines.
*/
private static void saveToLocal (long currentCount) {
try (java.io.Writer w = new java.io.BufferedWriter(new java.io.OutputStreamWriter(new java.io.FileOutputStream(FNAME), "utf-8"))) {
w.write(PREFIX + "," + SEQ_ID.longValue() + "," + MINVALUE + "," + MAXVALUE + "," + CACHEVALUE + "," + currentCount);
w.flush();
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Load the sequence file content into String.
* @return
*/
private String loadToString() {
try {
return new String(java.nio.file.Files.readAllBytes(java.nio.file.Paths.get(FNAME)));
} catch (Exception e) {
e.printStackTrace();
}
return "";
}
/**
* Utility method to round up num to next multiple value. This method is used to calculate the next cache value.
* <p>
* (Reference: http://stackoverflow.com/questions/18407634/rounding-up-to-the-nearest-hundred)
* <p>
* <u><b>Sample output:</b></u>
* <pre>
* System.out.println(roundUpNumberByMultipleValue(9,10)); = 10
* System.out.println(roundUpNumberByMultipleValue(10,10)); = 20
* System.out.println(roundUpNumberByMultipleValue(19,10)); = 20
* System.out.println(roundUpNumberByMultipleValue(100,10)); = 110
* System.out.println(roundUpNumberByMultipleValue(109,10)); = 110
* System.out.println(roundUpNumberByMultipleValue(110,10)); = 120
* System.out.println(roundUpNumberByMultipleValue(119,10)); = 120
* </pre>
*
* @param num Value must be greater and equals to positive integer 1.
* @param multiple Value must be greater and equals to positive integer 1.
* @return
*/
private long roundUpNumberByMultipleValue(long num, long multiple) {
if (num<=0) num=1;
if (multiple<=0) multiple=1;
if (num % multiple != 0) {
long division = (long) ((num / multiple) + 1);
return division * multiple;
} else {
return num + multiple;
}
}
/**
* Main method for testing purpose.
* @param args
*/
public static void main(String[] args) throws Exception {
//FixLengthIDSequence(Filename, prefix, initvalue, minvalue, maxvalue, cache)
FixLengthIDSequence seq = new FixLengthIDSequence(null,"H",50,1,999,10);
for (int i=0; i<12; i++) {
System.out.println(seq.nextVal());
Thread.sleep(1000);
//if (i==8) { System.exit(0); }
}
}
}
要测试代码，让序列正常运行。您可以按 Ctrl+C 来模拟服务器崩溃。下一个序列号将从 NextSnapshot+1 继续。
【讨论】：
冷你使用其他一些独特数据来源的前 9 位数字，例如：
考虑了两秒钟，这些都不是唯一的，但您可以将它们用作哈希函数的种子值，如另一个答案中所建议的那样。
【讨论】：