基於redis的分佈式自增序列

RedisAtomicInteger，RedisAtomicLong 是spring-data-redis.jar提供的方法，springboot加入redis模塊自動引入

1. 這兩個類與AtomicInteger的區別是，一個是分佈式自增，一個是jvm內自增
2. int和long增到最大時會變成負數，處理方法是，檢測到負數時設置爲0，見下面代碼
3. 性能，不加此調用，併發量360；加了此調用，併發量330，看出對性能影響很小

package com.example.demo.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.support.atomic.RedisAtomicInteger;
import org.springframework.data.redis.support.atomic.RedisAtomicLong;
import org.springframework.stereotype.Service;

import javax.annotation.PostConstruct;

@Service
public class KeyGenertService {
    @Autowired
    RedisTemplate<String, String> redisTemplate;

    private RedisAtomicInteger counter_int_tx;
    private RedisAtomicLong counter_long_tx2;

    @PostConstruct
    public void init() {
        counter_int_tx = new RedisAtomicInteger("int_tx", redisTemplate.getConnectionFactory());
        counter_long_tx2 = new RedisAtomicLong("long_tx2", redisTemplate.getConnectionFactory());
    }
    
    public int generate_int_tx() {
        int i = counter_int_tx.incrementAndGet();
        if (i < 0) {
            synchronized (this) {
                i = counter_int_tx.incrementAndGet();
                if (i < 0) {
                    counter_int_tx.set(0);
                    i = 0;
                }
            }
        }
        return i;
    }

    public long generate_long_tx2() {
        long i = counter_long_tx2.incrementAndGet();
        if (i < 0) {
            synchronized (this) {
                i = counter_long_tx2.incrementAndGet();
                if (i < 0) {
                    counter_long_tx2.set(0);
                    i = 0;
                }
            }
        }
        return i;
    }
}