番石榴 11:缓存在 5 分钟刷新后不起作用

Question

我们在每 30 秒运行一次的 HeartBeat 线程中有以下方法，我们引入了 Guava 缓存，刷新 5 分钟，如下所示ClientsDAO.getClients()这样我们就不会每 30 秒访问一次数据库。

private List<String> getClients() {
        final Supplier<List<String>> supplier = () ->  ClientsDAO.getClients();
        if(Server.CACHE_REFRESH_DURATION <=0)
            return supplier.get();
        else{
        LOG.debug("Fetching Clients from cache, duration = "+Server.CACHE_REFRESH_DURATION+". timeunit = "+Server.CACHE_REFRESH_TIMEUNIT);  
        return Suppliers.memoizeWithExpiration(supplier, Server.CACHE_REFRESH_DURATION, Server.CACHE_REFRESH_TIMEUNIT).get();
        }       
    }

正如您在下面的日志中看到的那样，每次线程HeartBeat运行它访问数据库而不是从缓存中获取它时。 有人可以帮我修复它吗？

[Jun 10 10:16:05] pool-16-thread-1 | DEBUG | com.server.Heartbeat | Fetching Clients from cache, duration = 5. timeunit = MINUTES
[Jun 10 10:16:05] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Getting DB connection
[Jun 10 10:16:05] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Queried for Clients
[Jun 10 10:16:35] pool-16-thread-1 | DEBUG | com.server.Heartbeat | Fetching Clients from cache, duration = 5. timeunit = MINUTES
[Jun 10 10:16:35] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Getting DB connection
[Jun 10 10:16:35] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Queried for Clients
[Jun 10 10:17:05] pool-16-thread-1 | DEBUG | com.server.Heartbeat | Fetching Clients from cache, duration = 5. timeunit = MINUTES
[Jun 10 10:17:05] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Getting DB connection
[Jun 10 10:17:05] pool-16-thread-1 | DEBUG | com.server.ClientsDAO | Queried for Clients

Answer 1

你从不重用Suppliers.memoizeWithExpiration所以它总是一个新的调用

您在每次调用时都会创建一个新的记忆供应商，因此

您基本上每次都会进行一个新调用，因为新的记忆供应商是空的，因此会传播调用以填充自身。你应该只创建一次记忆供应商，并像这样反复调用它：

private final Supplier<List<Client>> getClientsSupplier = Suppliers.memoizeWithExpiration(ClientsDao::getClients, Server.CACHE_REFRESH_DURATION, Server.CACHE_REFRESH_TIMEUNIT);
public List<Client> getClients() {
  return getClientsSupplier.get();
}