Guava庫學習：學習Guava Cache（七）RemovalListener（2）

    原文地址：Guava庫學習：學習Guava Cache（七）RemovalListener（2）_RemovalListeners   

    接着上一篇Guava庫學習：學習Guava Cache（七）RemovalListener（1）_RemovalNotification，咱們繼續Guava Cache RemovalListener的學習，學習Guava Cache（七）RemovalListener（2）_RemovalListeners。

    RemovalListeners

    RemovalListeners可以幫助咱們異步的處理，緩存條目移除後的通知，爲了讓咱們的Listener能夠在條目被移除時異步的處理通知，咱們能夠像下面這樣調用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，咱們經過構造好的RemovalListener和executorService實例，並被它們做爲參數傳入 RemovalListeners.asynchronous的方法中。這個方法返回了一個RemovalListener實例，將異步的處理移除條目後的通知，這個步驟會發生在咱們將這個RemovalListener註冊到CacheBuilder實例後。