Java开发利器之Guava Cache的使用教程

private Cache<String, User> cache = CacheBuilder.newBuilder()
            .expireAfterWrite(3, TimeUnit.SECONDS)//写入多久没更新自动过期，先删除，后load
            .removalListener(new RemovalListener<Object, Object>() {
                @Override
                public void onRemoval(RemovalNotification<Object, Object> notification) {
                    LOGGER.info("{} remove {}",LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")),notification.getKey());
                }
            })
            .initialCapacity(20) //初始化容量
            .concurrencyLevel(10) // 并发
            .maximumSize(100) //最多缓存数量
            .recordStats() // 开启统计
            .build();

@Override
    public User getUser(String id){
//        缓存不存在时，通过LocalCache锁机制，防止对数据库的高频访问
       User user;
       try {
           user = cache.get(id,()-> {
               LOGGER.info("缓存不存在,从loader加载数据");
               return userDao.get(id);
           });
       } catch (ExecutionException e) {
           throw new RuntimeException(e);
       }
        return user;
    }

    @Override
    public User saveOrUpdateUser(User user){
        userDao.saveOrUpdate(user);
        cache.put(user.getId(),user);
        return user;
    }

    @Override
    public void removeUser(String id){
        userDao.remove(id);
        cache.invalidate(id);
    }

private LoadingCache<String, User> cache = CacheBuilder.newBuilder()
            // 省略
            .build(new CacheLoader<String, User>() {
                @Override
                public User load(String key) throws Exception {
                    LOGGER.info("{} load {}",LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")),key);
                    return userDao.get(key);
                }

                @Override
                public ListenableFuture<User> reload(String key, User oldUser) throws Exception {
                    LOGGER.info("{} reload {}", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")),key);
                    ListenableFutureTask<User> listenableFutureTask = ListenableFutureTask.create(() -> userDao.get(key));
                    CompletableFuture.runAsync(listenableFutureTask);
                    return listenableFutureTask;
                }
            });

    @SneakyThrows
    @Override
    public User getUser(String id){
        // 缓存不存在或返回为null会抛出异常
        try {
            return cache.getUnchecked(id);
        } catch (Exception e) {
            return null;
        }
    }

    @Override
    public User saveOrUpdateUser(User user){
        cache.invalidate(user.getId());
        return userDao.saveOrUpdate(user);
    }

    @Override
    public void removeUser(String id){
        cache.invalidate(id);
        userDao.remove(id);
    }