1. 方法要求
在这个工具类中我们完成四个方法:
- 方法①:将任意Java对象序列化为json并存储在string类型的key中,并且可以设置TTL过期时间
- 方法②:将任意Java对象序列化为json并存储在string类型的key中,并且可以设置逻辑过期时间,用于处理缓存击穿问题
- 方法③:根据指定的key查询缓存,并反序列化为指定类型,利用缓存空值的方式解决缓存穿透问题
- 方法④:根据指定的key查询缓存,并反序列化为指定类型,需要利用逻辑过期解决缓存击穿问题
我们新建一个类,先把大致框架写出来,方法的参数可以边写边完善,但是我的方法参数已经完善好了:
@Component public class CacheClient { private final StringRedisTemplate stringRedisTemplate; public CacheClient(StringRedisTemplate stringRedisTemplate) { this.stringRedisTemplate = stringRedisTemplate; } //方法一 public void set(String key, Object value, Long time, TimeUnit unit) { } //方法二 public void setWithLogicExpire(String key, Object value, Long time, TimeUnit unit) { } //方法三 public <R, ID> R queryWithPassThrough(String keyPrefix, ID id, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { } //方法四 public <R, ID> R queryWithLogicalExpire(String prefix, ID id, String lockPre, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { } //线程池 private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10); //获取锁 private boolean tryLock(String key) { Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", LOCK_SHOP_TTL, TimeUnit.SECONDS); return BooleanUtil.isTrue(flag); } //释放锁 private void unLock(String key) { stringRedisTemplate.delete(key); } }
接下来我们可以不断完善这些方法。
1.1 方法一
public void set(String key, Object value, Long time, TimeUnit unit) { stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(value), time, unit); }
1.2 方法二
public void setWithLogicExpire(String key, Object value, Long time, TimeUnit unit) { RedisData redisData = new RedisData(); redisData.setData(value); redisData.setExpireTime(LocalDateTime.now().plusSeconds(unit.toSeconds(time))); stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(redisData)); }
1.3 方法三
public <R, ID> R queryWithPassThrough(String keyPrefix, ID id, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { String key = keyPrefix + id; //1.从redis中查询商铺缓存 String json = stringRedisTemplate.opsForValue().get(key); //2.判断是否存在 if (StrUtil.isNotBlank(json)) { //2.1.存在 return JSONUtil.toBean(json, type); } //2.2.不存在 //判断是否为空值 if (json != null) { //不为null,则必为空 return null; } //3.查询数据库 R r = dbFallback.apply(id); if (r == null) { //3.1.不存在,缓存空值 stringRedisTemplate.opsForValue().set(key, "", CACHE_NULL_TTL, TimeUnit.MINUTES); } else { //3.2.存在,缓存数据 this.set(key, r, time, unit); } return r; }
方法三用到了函数式编程,这里非常巧妙,顺便再贴一下调用方法是怎样调用的:
Shop shop = cacheClient.queryWithPassThrough(CACHE_SHOP_KEY,id,Shop.class,CACHE_SHOP_TTL,TimeUnit.MINUTES,this::getById);
1.4 方法四
public <R, ID> R queryWithLogicalExpire(String prefix, ID id, String lockPre, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { //1.从redis查询商铺缓存 String key = prefix + id; String json = stringRedisTemplate.opsForValue().get(key); //2.判断是否存在 if (StrUtil.isBlank(json)) { //未命中,直接返回空 return null; } //3.命中,判断是否过期 RedisData redisData = JSONUtil.toBean(json, RedisData.class); R r = JSONUtil.toBean((JSONObject) redisData.getData(), type); if (redisData.getExpireTime().isAfter(LocalDateTime.now())) { //3.1未过期,直接返回店铺信息 return r; } //3.2.已过期,缓存重建 //3.3.获取锁 String lockKey = lockPre + id; boolean flag = tryLock(lockKey); if (flag) { //3.4.获取成功 //4再次检查redis缓存是否过期,做double check json = stringRedisTemplate.opsForValue().get(key); //4.1.判断是否存在 if (StrUtil.isBlank(json)) { //未命中,直接返回空 return null; } //4.2.命中,判断是否过期 redisData = JSONUtil.toBean(json, RedisData.class); r = JSONUtil.toBean((JSONObject) redisData.getData(), type); if (redisData.getExpireTime().isAfter(LocalDateTime.now())) { //4.3.未过期,直接返回店铺信息 return r; } //4.4过期,返回旧数据 CACHE_REBUILD_EXECUTOR.submit(() -> { //5.重建缓存 try { R r1 = dbFallback.apply(id); this.setWithLogicExpire(key, r1, time, unit); } catch (Exception e) { throw new RuntimeException(e); } finally { //释放锁 unLock(lockKey); } }); } //7.获取失败,返回旧数据 return r; }
2. 完整工具类代码
@Component @Slf4j public class CacheClient { private final StringRedisTemplate stringRedisTemplate; public CacheClient(StringRedisTemplate stringRedisTemplate) { this.stringRedisTemplate = stringRedisTemplate; } public void set(String key, Object value, Long time, TimeUnit unit) { stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(value), time, unit); } public void setWithLogicExpire(String key, Object value, Long time, TimeUnit unit) { RedisData redisData = new RedisData(); redisData.setData(value); redisData.setExpireTime(LocalDateTime.now().plusSeconds(unit.toSeconds(time))); stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(redisData)); } public <R, ID> R queryWithPassThrough(String keyPrefix, ID id, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { String key = keyPrefix + id; //1.从redis中查询商铺缓存 String json = stringRedisTemplate.opsForValue().get(key); //2.判断是否存在 if (StrUtil.isNotBlank(json)) { //2.1.存在 return JSONUtil.toBean(json, type); } //2.2.不存在 //判断是否为空值 if (json != null) { //不为null,则必为空 return null; } //3.查询数据库 R r = dbFallback.apply(id); if (r == null) { //3.1.不存在,缓存空值 stringRedisTemplate.opsForValue().set(key, "", CACHE_NULL_TTL, TimeUnit.MINUTES); } else { //3.2.存在,缓存数据 this.set(key, r, time, unit); } return r; } public <R, ID> R queryWithLogicalExpire(String prefix, ID id, String lockPre, Class<R> type, Long time, TimeUnit unit, Function<ID, R> dbFallback) { //1.从redis查询商铺缓存 String key = prefix + id; String json = stringRedisTemplate.opsForValue().get(key); //2.判断是否存在 if (StrUtil.isBlank(json)) { //未命中,直接返回空 return null; } //3.命中,判断是否过期 RedisData redisData = JSONUtil.toBean(json, RedisData.class); R r = JSONUtil.toBean((JSONObject) redisData.getData(), type); if (redisData.getExpireTime().isAfter(LocalDateTime.now())) { //3.1未过期,直接返回店铺信息 return r; } //3.2.已过期,缓存重建 //3.3.获取锁 String lockKey = lockPre + id; boolean flag = tryLock(lockKey); if (flag) { //3.4.获取成功 //4再次检查redis缓存是否过期,做double check json = stringRedisTemplate.opsForValue().get(key); //4.1.判断是否存在 if (StrUtil.isBlank(json)) { //未命中,直接返回空 return null; } //4.2.命中,判断是否过期 redisData = JSONUtil.toBean(json, RedisData.class); r = JSONUtil.toBean((JSONObject) redisData.getData(), type); if (redisData.getExpireTime().isAfter(LocalDateTime.now())) { //4.3.未过期,直接返回店铺信息 return r; } //4.4过期,返回旧数据 CACHE_REBUILD_EXECUTOR.submit(() -> { //5.重建缓存 try { R r1 = dbFallback.apply(id); this.setWithLogicExpire(key, r1, time, unit); } catch (Exception e) { throw new RuntimeException(e); } finally { //释放锁 unLock(lockKey); } }); } //7.获取失败,返回旧数据 return r; } private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10); //获取锁 private boolean tryLock(String key) { Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", LOCK_SHOP_TTL, TimeUnit.SECONDS); return BooleanUtil.isTrue(flag); } //释放锁 private void unLock(String key) { stringRedisTemplate.delete(key); } }