import redis.clients.jedis.Jedis;

public class RedisLockExample {
    public static void main(String[] args) {
        Jedis jedis = new Jedis("localhost", 6379);
        String key = "resource_lock";
        String value = "lock_value";
        int expireTime = 100; // 過(guò)期時(shí)間，單位秒

        if (jedis.setnx(key, value) == 1) {
            jedis.expire(key, expireTime);
            try {
                // 業(yè)務(wù)代碼
                System.out.println("獲取鎖成功，執(zhí)行業(yè)務(wù)邏輯");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                jedis.del(key);
                System.out.println("釋放鎖");
            }
        } else {
            System.out.println("獲取鎖失敗");
        }
        jedis.close();
    }
}

- **缺點(diǎn)**：`SETNX`和`EXPIRE`兩個(gè)命令不是原子操作，如果在執(zhí)行完`SETNX`后，進(jìn)程崩潰或重啟，`EXPIRE`命令未執(zhí)行，鎖將無(wú)法釋放，導(dǎo)致其他客戶(hù)端永遠(yuǎn)無(wú)法獲取鎖。

import redis.clients.jedis.Jedis;

public class RedisLockWithTimeExample {
    public static void main(String[] args) {
        Jedis jedis = new Jedis("localhost", 6379);
        String key = "resource_lock";
        long expireTime = 10000; // 過(guò)期時(shí)間，單位毫秒

        long expires = System.currentTimeMillis() + expireTime;
        String expiresStr = String.valueOf(expires);

        if (jedis.setnx(key, expiresStr) == 1) {
            System.out.println("獲取鎖成功");
        } else {
            String currentValueStr = jedis.get(key);
            if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
                String oldValueStr = jedis.getSet(key, expiresStr);
                if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
                    System.out.println("獲取鎖成功");
                } else {
                    System.out.println("獲取鎖失敗，其他線程已更新鎖");
                }
            } else {
                System.out.println("獲取鎖失敗，鎖未過(guò)期");
            }
        }
        jedis.close();
    }
}

- **缺點(diǎn)**：過(guò)期時(shí)間是客戶(hù)端自己生成的，依賴(lài)系統(tǒng)時(shí)間，要求分布式環(huán)境下每個(gè)客戶(hù)端的時(shí)間必須同步。鎖過(guò)期時(shí)，并發(fā)多個(gè)客戶(hù)端同時(shí)請(qǐng)求，都執(zhí)行`getSet`，最終只有一個(gè)客戶(hù)端加鎖成功，但該客戶(hù)端鎖的過(guò)期時(shí)間可能被別的客戶(hù)端覆蓋。且該鎖沒(méi)有保存持有者的唯一標(biāo)識(shí)，可能被別的客戶(hù)端釋放。

import redis.clients.jedis.Jedis;
import java.util.Collections;

public class RedisLockWithLuaExample {
    public static void main(String[] args) {
        Jedis jedis = new Jedis("localhost", 6379);
        String key = "resource_lock";
        String value = "lock_value";
        int expireTime = 100; // 過(guò)期時(shí)間，單位秒

        String luaScript = "if redis.call('setnx', KEYS[1], ARGV[1]) == 1 then " +
                "redis.call('expire', KEYS[1], ARGV[2]) " +
                "else " +
                "return 0 " +
                "end";

        Object result = jedis.eval(luaScript, Collections.singletonList(key),
                Collections.singletonList(value + "," + expireTime));

        if (result.equals(1L)) {
            System.out.println("獲取鎖成功");
            try {
                // 業(yè)務(wù)代碼
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                jedis.del(key);
                System.out.println("釋放鎖");
            }
        } else {
            System.out.println("獲取鎖失敗");
        }
        jedis.close();
    }
}

import redis.clients.jedis.Jedis;

public class RedisSetLockExample {
    public static void main(String[] args) {
        Jedis jedis = new Jedis("localhost", 6379);
        String key = "resource_lock";
        String value = "lock_value";
        int expireTime = 100; // 過(guò)期時(shí)間，單位秒

        String result = jedis.set(key, value, "NX", "EX", expireTime);

        if ("OK".equals(result)) {
            System.out.println("獲取鎖成功");
            try {
                // 業(yè)務(wù)代碼
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                jedis.del(key);
                System.out.println("釋放鎖");
            }
        } else {
            System.out.println("獲取鎖失敗");
        }
        jedis.close();
    }
}

import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;

public class RedissonLockExample {
    public static void main(String[] args) {
        Config config = new Config();
        config.useSingleServer().setAddress("redis://localhost:6379");
        RedissonClient redissonClient = Redisson.create(config);

        RLock lock = redissonClient.getLock("resource_lock");

        try {
            boolean isLocked = lock.tryLock(10, 30, java.util.concurrent.TimeUnit.SECONDS);
            if (isLocked) {
                System.out.println("獲取鎖成功");
                // 業(yè)務(wù)代碼
            } else {
                System.out.println("獲取鎖失敗");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
            redissonClient.shutdown();
        }
    }
}

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Service;

@Service
public class UserServiceCacheAside {
    @Autowired
    private RedisTemplate<String, Object> redisTemplate;
    @Autowired
    private UserRepository userRepository;
    private static final String CACHE_KEY_PREFIX = "user:";
    private static final long CACHE_EXPIRATION = 30; // 緩存過(guò)期時(shí)間（分鐘）

    public User getUserById(Long userId) {
        String cacheKey = CACHE_KEY_PREFIX + userId;
        // 1. 查詢(xún)緩存
        User user = (User) redisTemplate.opsForValue().get(cacheKey);
        // 2. 緩存命中，直接返回
        if (user != null) {
            return user;
        }
        // 3. 緩存未命中，查詢(xún)數(shù)據(jù)庫(kù)
        user = userRepository.findById(userId).orElse(null);
        // 4. 將數(shù)據(jù)庫(kù)結(jié)果寫(xiě)入緩存（設(shè)置過(guò)期時(shí)間）
        if (user != null) {
            redisTemplate.opsForValue().set(cacheKey, user, CACHE_EXPIRATION, java.util.concurrent.TimeUnit.MINUTES);
        }
        return user;
    }

    public void updateUser(User user) {
        // 1. 先更新數(shù)據(jù)庫(kù)
        userRepository.save(user);
        // 2. 再刪除緩存
        String cacheKey = CACHE_KEY_PREFIX + user.getId();
        redisTemplate.delete(cacheKey);
    }
}