Guava库学习：学习Guava Cache（七）RemovalListener（2）

    原文地址：Guava库学习：学习Guava Cache（七）RemovalListener（2）_RemovalListeners   

    接着上一篇Guava库学习：学习Guava Cache（七）RemovalListener（1）_RemovalNotification，咱们继续Guava Cache RemovalListener的学习，学习Guava Cache（七）RemovalListener（2）_RemovalListeners。

    RemovalListeners

    RemovalListeners可以帮助咱们异步的处理，缓存条目移除后的通知，为了让咱们的Listener能够在条目被移除时异步的处理通知，咱们能够像下面这样调用RemovalListeners. asynchronous方法：

    private ExecutorService executor;
    private ListeningExecutorService executorService;

    @Before
    public void setUp() {
        executor = Executors.newCachedThreadPool();
        executorService = MoreExecutors.listeningDecorator(executor);
    }

    @Test
    public void testRemovalListener() {
        RemovalListener<String, TradeAccount> myRemovalListener = new
                RemovalListener<String, TradeAccount>() {
                    @Override
                    public void onRemoval(RemovalNotification<String,
                            TradeAccount> notification) {
                        //Do something here
                    }
                };
        RemovalListener<String, TradeAccount> removalListener =
                RemovalListeners.asynchronous(myRemovalListener, executorService);
    }

    上面，咱们经过构造好的RemovalListener和executorService实例，并被它们做为参数传入 RemovalListeners.asynchronous的方法中。这个方法返回了一个RemovalListener实例，将异步的处理移除条目后的通知，这个步骤会发生在咱们将这个RemovalListener注册到CacheBuilder实例后。