java - 使用 curator treeCache 时，如何确保缓存准备就绪？

Question

使用 curator treeCache 时，如何确保缓存准备就绪？

在 cache.start() 之后，如果我立即调用 getCurrentData，它将返回 null，那么如何确保缓存准备就绪？，有人可以给我举个例子吗？谢谢

client = CuratorFrameworkFactory.builder()
             .connectString(connectionString)
             .retryPolicy(new ExponentialBackoffRetry(zkConnectionTimeoutMs, 3))
             .sessionTimeoutMs(zkSessionTimeoutMs)
             .build();
client.start();

cache = new TreeCache(client, rootPath);
cache.start();
ChildData child = cache.getCurrentData(rootPath); // child is null
Thread.sleep(50);   // must sleep for a while
child = cache.getCurrentData(rootPath); // child is ok

Answer 1

您可以为 Treecache 添加一个监听器并监听 INITIALIZED 事件。

    Semaphore sem = new Semaphore(0);
    client = CuratorFrameworkFactory.builder()
                                 .connectString(connectionString)
                                 .retryPolicy(new ExponentialBackoffRetry(zkConnectionTimeoutMs, 3))
                                 .sessionTimeoutMs(zkSessionTimeoutMs)
                                 .build();
        client.start();

        cache = new TreeCache(client, rootPath);
                    cache.start();

        TreeCacheListener listener = new TreeCacheListener() {

                                    @Override
                                    public void childEvent(CuratorFramework client, TreeCacheEvent event)
                                            throws Exception {
                                        switch (event.getType()) {
                                        case INITIALIZED: {

                                          sem.release();

                                        }

                                    }

                                };
        cache.getListenable().addListener(listener);
       sem.acquire();
child = cache.getCurrentData(rootPath);