非自增编号字段，避免生成重复编号(以pdfNo编号为例)
有个场景，用户查询延误航班信息，然后生产一个编号，默认第一个编号是1000001，其后新增的编号默认自增加1。每次有人来查延误信息，如果延误信息存在，则取查询数据库pdfNo字段，查询最大的编号，然后+1后，再插入一条新的延误记录。这样会造成多人同时查询，并生成延误记录是,pdfNo的编号会重复现象。
经过分析，俺们组长说，有2中多种解决方案，一种是分布式锁方案，一种是insert into select from方案，一种是RedisLock方案。
本人愚笨，说下insert into select from, 和 RedisLock方案
insert into select from：
在入库的时候，查询下最大pdfNo，然后加一入库
方法一： INSERT INTO Websites (name, country) SELECT app_name, country FROM apps WHERE id=1;
二： 表结构如上图 insert into test_aaa (title, pdfno) select "hello", max(pdfno) +1 as pdfmax from test_aaa;
RedisLock方法
VariableKeyLock.java
import java.util.concurrent.locks.Lock;
/**
* 可变key锁
*
* @author zhangyang-b
*/
public interface VariableKeyLock extends Lock {
boolean tryLock(String key);
void lock(String key);
void unlock(String key);
}
RedisLock.java
public class RedisLock implements VariableKeyLock {
public static final String LOCK = "LOCK";
@Autowired
private RedisConnectionFactory factory;
private ThreadLocal<String> localValue = new ThreadLocal<String>();
/**
* 解锁lua脚本
*/
private static final String UNLOCK_LUA =
"if redis.call(\"get\",KEYS[1]) == ARGV[1] then return redis.call(\"del\",KEYS[1]) else return 0 end";
@Override
public void lock() {
if (!tryLock()) {
try {
Thread.sleep(new Random().nextInt(10) + 1);
} catch (InterruptedException e) {
log.error(e.getMessage(), e);
}
lock();
}
}
@Override
public void lock(String key) {
if (!tryLock(key)) {
try {
Thread.sleep(new Random().nextInt(10) + 1);
} catch (InterruptedException e) {
log.error(e.getMessage(), e);
}
lock(key);
}
}
@Override
public boolean tryLock() {
RedisConnection connection = null;
try {
connection = factory.getConnection();
Jedis jedis = (Jedis)connection.getNativeConnection();
String value = UUID.randomUUID().toString();
localValue.set(value);
String ret = jedis.set(LOCK, value, "NX", "PX", 10000);
return ret != null && "OK".equals(ret);
} catch (Exception e) {
log.error(e.getMessage(), e);
} finally {
if (connection != null) {
connection.close();
}
}
return false;
}
@Override
public boolean tryLock(String key) {
RedisConnection connection = null;
try {
connection = factory.getConnection();
Jedis jedis = (Jedis)connection.getNativeConnection();
String value = UUID.randomUUID().toString();
localValue.set(value);
String ret = jedis.set(key, value, "NX", "PX", 10000);
return ret != null && "OK".equals(ret);
} catch (Exception e) {
log.error(e.getMessage(), e);
} finally {
if (connection != null) {
connection.close();
}
}
return false;
}
@Override
public void unlock() {
String script = UNLOCK_LUA;
RedisConnection connection = null;
try {
connection = factory.getConnection();
Object jedis = connection.getNativeConnection();
if (jedis instanceof Jedis) {
((Jedis)jedis).eval(script, Arrays.asList(LOCK), Arrays.asList(localValue.get()));
} else if (jedis instanceof JedisCluster) {
((JedisCluster)jedis).eval(script, Arrays.asList(LOCK), Arrays.asList(localValue.get()));
}
} catch (Exception e) {
log.error(e.getMessage(), e);
} finally {
if (connection != null) {
connection.close();
}
}
}
@Override
public void unlock(String key) {
String script = UNLOCK_LUA;
RedisConnection connection = null;
try {
connection = factory.getConnection();
Object jedis = connection.getNativeConnection();
if (jedis instanceof Jedis) {
((Jedis)jedis).eval(script, Arrays.asList(key), Arrays.asList(localValue.get()));
} else if (jedis instanceof JedisCluster) {
((JedisCluster)jedis).eval(script, Arrays.asList(key), Arrays.asList(localValue.get()));
}
} catch (Exception e) {
log.error(e.getMessage(), e);
} finally {
if (connection != null) {
connection.close();
}
}
}
}
用法：
redisLock.lock(key名);
try{
int maxPdfNo = 0;
try{
maxPdfNo = flightDelayPdfJService.queryMaxPdfNo();
}catch (Exception e){
e.printStackTrace();
}
if(maxPdfNo > 0){
return maxPdfNo + 1;
}else{
return 1000001;
}
}finally {
redisLock.unlock(key名);
}
非自增编号字段，避免生成重复编号(以pdfNo编号为例)RedisLock/ReadLock
原文：https://www.cnblogs.com/achengmu/p/10973931.html