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💌EVAL帮助文档

EVAL-Redis命令参考

​

传参数的格式

​其中 "return {KEYS[1],KEYS[2],ARGV[1],ARGV[2]}" 是被求值的 Lua 脚本，数字 2 指定了键名参数的数量， key1 和 key2 是键名参数，分别使用 KEYS[1] 和 KEYS[2] 访问，而最后的 argv1 和 argv2 则是附加参数，可以通过 ARGV[1] 和 ARGV[2] 访问它们

• redis.call()

​

• eval执行scan

源生scan命令

//例如模糊迭代初始游标为0 前缀为'user.'的Key 期望获取5条的命令
scan 0 match user.* count 5

使用eval执行脚本

eval "return redis.call('scan',ARGV[1],'match',KEYS[1],'count',ARGV[2])" 1 user.* 0 5

💌SpringBoot调用LUA脚本 

​

@SpringBootTest
public class AppTests_Lua {

    @Resource(name = "redisTemplate")
    private ValueOperations<String, User> valueOperations;

    @Autowired
    private StringRedisTemplate stringRedisTemplate;

    @Test
    void test1() {
        for (int i =1 ;i<11;i++){
            User user = User.builder().name(i+"号张").age(18).build();
            valueOperations.set("user."+i,user);
        }
    }
    @Test
    void test2(){
        String lua = "return redis.call('scan',ARGV[1],'match',KEYS[1],'count',ARGV[2])";
        RedisScript<List> redisScript = RedisScript.of(lua,List.class);
        List<String> keys = new ArrayList<>();
        keys.add("user.*");
        List execute = stringRedisTemplate.execute(redisScript, keys, "0", "5");
    }
}

​

完整的迭代过程

    @Test
    void test2() {
        String lua = "return redis.call('scan',ARGV[1],'match',KEYS[1],'count',ARGV[2])";
        RedisScript<List> redisScript = RedisScript.of(lua, List.class);
        List<String> keys = new ArrayList<>();
        keys.add("user.*");
        String cursor = "0";
        do {
            List results = stringRedisTemplate.execute(redisScript, keys, cursor, "5");
            cursor = (String) results.get(0);
            List<String> results_keys = (List<String>) results.get(1);
            System.out.println(cursor);
            System.out.println(results_keys);
        } while (!"0".equals(cursor));
    }

 简单的get两种方式(KEYS提前预编译好了,与ARGV的区别只是效率不同)

    @Test
    void test3() {
        String lua = "return redis.call('mget',KEYS[1],KEYS[2])";
        RedisScript<List> redisScript = RedisScript.of(lua, List.class);
        List<String> keys = new ArrayList<>();
        keys.add("user.1");
        keys.add("user.10");
        List results = stringRedisTemplate.execute(redisScript, keys);
    }

    @Test
    void test3() {
        String lua = "return redis.call('mget',ARGV[1],ARGV[2])";
        RedisScript<List> redisScript = RedisScript.of(lua, List.class);
        List<String> keys = new ArrayList<>();
        List results = stringRedisTemplate.execute(redisScript, keys,"user.1","user.10");
    }

💌解决库存负数问题

@SpringBootTest
class AppTests_DecrBy {

    @Resource(name = "redisTemplate")
    private ValueOperations<String, Integer> valueOperations;

    @Autowired
    private StringRedisTemplate stringRedisTemplate;

    //定义一个产品
    private final static String productKey = "product01";

    @Test
    void test1() throws InterruptedException {
        //设置初始化库存5个
        valueOperations.set(productKey, 5);
        //获取线程池
        ExecutorService executorService = Executors.newCachedThreadPool();
        //模拟开启10个线程
        for (int i = 1; i <= 10; i++) {
            //模拟扣减i个库存量(qty)
            int finalI = i;
            //开启线程执行
            executorService.execute(() -> {
                doing(finalI);
            });
        }
        //防止主线程停止,导致模拟线程不执行
        Thread.sleep(60 * 1000);
    }
    //lua脚本语言
    private static String lua ;
    static {
        StringBuilder sb = new StringBuilder();
        sb.append(" local key = KEYS[1]  ");
        sb.append(" local qty = ARGV[1]  ");
        sb.append(" local redis_qty = redis.call('get',key) ");
        sb.append(" if  tonumber(redis_qty) >= tonumber(qty) ");
        sb.append(" then  ");
        sb.append("   redis.call('decrby',key,qty) ");
        sb.append("   return -1 ");
        sb.append(" else ");
        sb.append("   return tonumber(redis_qty) ");
        sb.append(" end  ");
        lua = sb.toString();
    }

    private void doing(Integer qty){
        RedisScript<Long> redisScript = RedisScript.of(lua,Long.class);
        List<String> keys = new ArrayList<>();
        keys.add(productKey);
        Long ret = stringRedisTemplate.execute(redisScript, keys,qty.toString());
        if(ret.intValue()==-1){
            System.out.println(StrUtil.format("{},扣减成功,扣减数量:{}",Thread.currentThread().getName(),qty));
        }else{
            System.out.println(StrUtil.format("{},库存不足,需求量:{},库存量:{}",Thread.currentThread().getName(),qty,ret));
        }
    }
}

​

​

核心代码逻辑

    //lua脚本语言
    //local定义变量的修饰符
    //tonumber将字符串转换为数字类型
    //redis.call('get',key)获取当前库存量
    //redis.call('decrby',key,qty)扣减所需的库存量
    //求量小于库存量时扣减成功返回-1,需求量大于库存量时返回所剩库存量
    //最后将lua语言转成字符串
    private static String lua ;
    static {
        StringBuilder sb = new StringBuilder();
        sb.append(" local key = KEYS[1]  ");
        sb.append(" local qty = ARGV[1]  ");
        sb.append(" local redis_qty = redis.call('get',key) ");
        sb.append(" if  tonumber(redis_qty) >= tonumber(qty) ");
        sb.append(" then  ");
        sb.append("   redis.call('decrby',key,qty) ");
        sb.append("   return -1 ");
        sb.append(" else ");
        sb.append("   return tonumber(redis_qty) ");
        sb.append(" end  ");
        lua = sb.toString();
    }