RedisTemplate实现分布式锁

使用RedisTemplate的execute的回调方法，里面使用Setnx方法

Setnx就是，如果没有这个key，那么就set一个key-value, 但是如果这个key已经存在，那么将不会再次设置，get出来的value还是最开始set进去的那个value.

接下来我们用代码的形式展现:

package com.shuige.components.cache.redis;
  
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.ValueOperations;
import org.springframework.stereotype.Component;
  
import java.util.Objects;
import java.util.concurrent.TimeUnit;
  
/**
 * Description: 通用Redis帮助类
 * User: zhouzhou
 * Date: 2018-09-05
 * Time: 15:39
 */
@Component
public class CommonRedisHelper {
 
    //锁名称
    public static final String LOCK_PREFIX = "redis_lock";
    //加锁失效时间，毫秒
    public static final int LOCK_EXPIRE = 300; // ms
  
    @Autowired
    RedisTemplate redisTemplate;
  
    
    /**
     *  最终加强分布式锁
     *
     * @param key key值
     * @return 是否获取到
     */
    public boolean lock(String key){
        String lock = LOCK_PREFIX + key;
        // 利用lambda表达式
        return (Boolean) redisTemplate.execute((RedisCallback) connection -> {
  
            long expireAt = System.currentTimeMillis() + LOCK_EXPIRE + 1;
            Boolean acquire = connection.setNX(lock.getBytes(), String.valueOf(expireAt).getBytes());
  
  
            if (acquire) {
                return true;
            } else {
  
                byte[] value = connection.get(lock.getBytes());
  
                if (Objects.nonNull(value) && value.length > 0) {
  
                    long expireTime = Long.parseLong(new String(value));
                     // 如果锁已经过期
                    if (expireTime < System.currentTimeMillis()) {
                        // 重新加锁，防止死锁
                        byte[] oldValue = connection.getSet(lock.getBytes(), String.valueOf(System.currentTimeMillis() + LOCK_EXPIRE + 1).getBytes());
                        return Long.parseLong(new String(oldValue)) < System.currentTimeMillis();
                    }
                }
            }
            return false;
        });
    }
  
    /**
     * 删除锁
     *
     * @param key
     */
    public void delete(String key) {
        redisTemplate.delete(key);
    }
  
}

如何使用呢,导入工具类后:

CommonRedisHelper redisHelper = new CommonRedisHelper();

1	`boolean` `lock = redisHelper.lock(key);`

if (lock) {
            // 执行逻辑操作
            redisHelper.delete(key);
        } else {
            // 设置失败次数计数器, 当到达5次时, 返回失败
            int failCount = 1;
            while(failCount <= 5){
                // 等待100ms重试
                try {
                    Thread.sleep(100l);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (redisHelper.lock(key)){
                   // 执行逻辑操作
                    redisHelper.delete(key);
                }else{
                    failCount ++;
                }
            }
            throw new RuntimeException("现在创建的人太多了, 请稍等再试");
        }