分庫分表時通常有必要自定義生成uuid，大企業通常有本身的uuid生成服務，其餘它的實現很簡單。咱們以訂單號爲例，組成能夠是"業務標識號+年月日+當日自增數字格式化"，如0001201608140000020。固然，若是咱們用"業務標識號+用戶惟一標識+當前時間"也是能夠達到uuid的目的的，但用戶惟一標識是敏感信息且可能不太方便處理爲數字，因此弄一套uuid生成服務是頗有必要的。本文就來研究下怎麼實現自增數字，且性能能知足企業中的多方業務調用。起初，我想的是DB+Redis，後來想一想用Redis不只會相對下降穩定性，更是一種捨近求遠的作法，因此，我最終的作法是DB+本地緩存(內存)。不說了，直接上代碼。java
public class UuidModel implements Serializable {
private static final long serialVersionUID = 972714740313784893L;
private String name;
private long start;
private long end;
// above is DB column
private long oldStart;
private long oldEnd;
private long now;
package com.itlong.bjxizhan.uuid;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.List;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
/**
* Created by shenhongxi on 2016/8/12.
*/
public class UuidContext {
private static final Logger log = LoggerFactory.getLogger(UuidContext.class);
// 緩存DB中的截止數
public static ConcurrentMap<String, Long> endCache = new ConcurrentHashMap<String,Long>();
// 緩存當前增長到的數值
public static ConcurrentMap<String, Long> nowCache = new ConcurrentHashMap<String,Long>();
// 緩存共享對象
public static ConcurrentMap<String, UuidModel> uuidCache = new ConcurrentHashMap<String, UuidModel>();
// 緩存配置
public static ConcurrentMap<String, Config> configCache = new ConcurrentHashMap<String, Config>();
static UuidDao uuidDao;
/**
* 根據名稱更新號段 直至成功
* @param um
* @return
*/
public static UuidModel updateUuid(UuidModel um, int length){
boolean updated = false;
do{
UuidModel _um = uuidDao.findByName(um.getName());
int cacheSize = 1000;
Config config = getConfig(um.getName());
if (config != null) {
cacheSize = config.getCacheSize();
}
// 判斷是否須要重置 條件爲：1.配置的重置數<新段的截止數 則須要重置
// 2.新段的截止數大於須要獲取的位數 則須要重置
long resetNum = config.getResetNum();
// 取得新段的截止數
long newEnd = _um.getEnd() + cacheSize;
um.setOldEnd(_um.getEnd());
um.setOldStart(_um.getStart());
if ((resetNum < newEnd) || (String.valueOf(newEnd).length() > length)) {
// 須要重置爲0開始段
um.setStart(0);
um.setEnd(cacheSize);
} else {
// 取新段
um.setStart(_um.getEnd());
um.setEnd(_um.getEnd() + cacheSize);
}
// 最終的更新成功保證了多實例部署時，各實例持有的號段不一樣
updated = uuidDao.update(um);
} while (!updated);
return um;
}
/**
* 載入內存
* @param um
*/
public static void loadMemory(UuidModel um){
endCache.put(um.getName(), um.getEnd());
nowCache.put(um.getName(), um.getStart());
uuidCache.put(um.getName(), um);
}
public static Config getConfig(String name) {
Config config = configCache.get(name);
if (config == null) {
config = configCache.get("default");
}
return config;
}
}
package com.itlong.bjxizhan.uuid;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
* Created by shenhongxi on 2016/8/12.
*/
public class UuidServiceImpl implements UuidService {
private static final Logger log = LoggerFactory.getLogger(UuidServiceImpl.class);
private UuidDao uuidDao;
@Override
public String nextUuid(String name) {
// 日期 + format(nextUuid(name, cacheSize, length))
}
private synchronized long nextUuid(String name, int cacheSize, int length) {
UuidModel um = UuidContext.uuidCache.get(name);
Long nowUuid = null;
try {
if (um != null) {
synchronized (um) {
nowUuid = UuidContext.nowCache.get(name);
Config cm = UuidContext.getConfig(name);
// 判斷是否到達預警值
if (UuidContext.nowCache.get(name).intValue() == cm.getWarnNum()) {
log.warn("警告:" + name + "號段已達到預警值.");
}
log.info("dbNum:" + UuidContext.endCache.get(name)
+ ",nowNum:" + UuidContext.nowCache.get(name));
// 判斷內存中號段是否用完
if (UuidContext.nowCache.get(name).compareTo(UuidContext.endCache.get(name)) >= 0) {
// 更新號段
UuidContext.updateUuid(um, length);
nowUuid = um.getStart() + 1;
UuidContext.endCache.put(name, um.getEnd());
UuidContext.nowCache.put(name, nowUuid);
} else {
nowUuid += 1;
// 是否須要重置 判斷自增號位數是否大於length參數
if (String.valueOf(nowUuid).length() > length) {
// 更新號段，須要重置
nowUuid = 1l;
UuidContext.updateUuid(um, 0);
UuidContext.endCache.put(name, um.getEnd());
UuidContext.nowCache.put(name, nowUuid);
UuidContext.uuidCache.put(name, um);
} else {
// 直接修改緩存的值就能夠了
UuidContext.nowCache.put(name, nowUuid);
}
}
}
} else {
synchronized (this) {
um = UuidContext.uuidCache.get(name);
if (um != null) {
return nextUuid(name, cacheSize, length);
}
nowUuid = 1l;
// 若是緩存不存在，那麼就新增到數據庫
UuidModel um2 = new UuidModel();
um2.setName(name);
um2.setStart(0);
um2.setEnd(cacheSize);
uuidDao.insert(um2);
// 還要同時在緩存的map中加入
UuidContext.endCache.put(name, um2.getEnd());
UuidContext.nowCache.put(name, nowUuid);
UuidContext.uuidCache.put(name, um2);
}
}
} catch (Exception e) {
log.error("生成uuid error", e);
if (e.getMessage() != null && (e.getMessage().indexOf("UNIQUE KEY") >= 0 ||
e.getMessage().indexOf("PRIMARY KEY") >= 0)) {
UuidModel _um = new UuidModel();
_um.setName(name);
// 更新號段
UuidContext.updateUuid(_um, length);
// 載入緩存
UuidContext.loadMemory(_um);
// 繼續獲取
return nextUuid(name, cacheSize, length);
}
throw new RuntimeException("生成uuid error");
}
return nowUuid;
}
}
值得一提的是，DB+本地緩存的思路一樣能夠用於搶購時的庫存計算。數據庫