Mastering Redis Distributed Locks with Jedis: A Step-by-Step Guide

This article explains how to implement a Redis distributed lock using Jedis in Java, suitable for interview scenarios, and demonstrates a simulated high‑concurrency order‑grabbing case.

Jedis NX Lock Creation

It describes the lock strategy, expiration handling, and provides the Maven dependency needed.

<dependency>
    <groupId>redis.clients</groupId>
    <artifactId>jedis</artifactId>
</dependency>

The setnx method uses the NX and PX options to ensure only one client acquires the lock and to set an automatic expiration.

public boolean setnx(String key, String val) {
    Jedis jedis = null;
    try {
        jedis = jedisPool.getResource();
        if (jedis == null) {
            return false;
        }
        return jedis.set(key, val, "NX", "PX", 1000 * 60)
                .equalsIgnoreCase("ok");
    } catch (Exception ex) {
    } finally {
        if (jedis != null) {
            jedis.close();
        }
    }
    return false;
}

Lock Deletion

To safely release a lock, the same value must be provided; a Lua script performs an atomic check‑and‑delete.

public int delnx(String key, String val) {
    Jedis jedis = null;
    try {
        jedis = jedisPool.getResource();
        if (jedis == null) {
            return 0;
        }
        StringBuilder sbScript = new StringBuilder();
        sbScript.append("if redis.call('get','").append(key).append("')'"
                .append("=='").append(val).append("' then ")
                .append("return redis.call('del','").append(key).append("') ")
                .append("else return 0 end");
        return Integer.valueOf(jedis.eval(sbScript.toString()).toString());
    } catch (Exception ex) {
    } finally {
        if (jedis != null) {
            jedis.close();
        }
    }
    return 0;
}

Simulating 100k Concurrent Orders

The example initializes a small stock, creates 100,000 virtual users, and uses parallel streams to mimic a flash‑sale scenario where each user repeatedly tries to acquire the lock within a timeout.

// total stock
private long nKuCuen = 0;
private String shangpingKey = "computer_key";
private int timeout = 30 * 1000;

@GetMapping("/qiangdan")
public List<String> qiangdan() {
    List<String> shopUsers = new ArrayList<>();
    List<String> users = new ArrayList<>();
    IntStream.range(0, 100000).parallel().forEach(b -> {
        users.add("神牛-" + b);
    });
    nKuCuen = 10;
    users.parallelStream().forEach(b -> {
        String shopUser = qiang(b);
        if (!StringUtils.isEmpty(shopUser)) {
            shopUsers.add(shopUser);
        }
    });
    return shopUsers;
}

private String qiang(String b) {
    long startTime = System.currentTimeMillis();
    while ((startTime + timeout) >= System.currentTimeMillis()) {
        if (nKuCuen <= 0) break;
        if (jedisCom.setnx(shangpingKey, b)) {
            try {
                if (nKuCuen <= 0) break;
                TimeUnit.SECONDS.sleep(1);
                nKuCuen -= 1;
                return b + "抢单成功，所剩库存：" + nKuCuen;
            } finally {
                jedisCom.delnx(shangpingKey, b);
            }
        }
    }
    return "";
}

Images below show a successful lock acquisition, the execution log, and the final list of users who obtained the order.