Zookeeper Java 客户端 ——Apache Curator

<dependencies>
    <!--Curator 相关依赖-->
    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-framework</artifactId>
        <version>4.0.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-recipes</artifactId>
        <version>4.0.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.zookeeper</groupId>
        <artifactId>zookeeper</artifactId>
        <version>3.4.13</version>
    </dependency>
    <!--单元测试相关依赖-->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>
</dependencies>

public class BasicOperation {

    private CuratorFramework client = null;
    private static final String zkServerPath = "192.168.0.226:2181";
    private static final String nodePath = "/hadoop/yarn";

    @Before
    public void prepare() {
        // 重试策略
        RetryPolicy retryPolicy = new RetryNTimes(3, 5000);
        client = CuratorFrameworkFactory.builder()
        .connectString(zkServerPath)
        .sessionTimeoutMs(10000).retryPolicy(retryPolicy)
        .namespace("workspace").build();  //指定命名空间后，client 的所有路径操作都会以/workspace 开头
        client.start();
    }

    @After
    public void destroy() {
        if (client != null) {
            client.close();
        }
    }
}

/**
 * @param baseSleepTimeMs 重试之间等待的初始时间
 * @param maxRetries 最大重试次数
 * @param maxSleepMs 每次重试间隔的最长睡眠时间（毫秒）
 */
ExponentialBackoffRetry(int baseSleepTimeMs, int maxRetries, int maxSleepMs)    

@Test
public void getStatus() {
    CuratorFrameworkState state = client.getState();
    System.out.println("服务是否已经启动:" + (state == CuratorFrameworkState.STARTED));
}

@Test
public void createNodes() throws Exception {
    byte[] data = "abc".getBytes();
    client.create().creatingParentsIfNeeded()
            .withMode(CreateMode.PERSISTENT)      //节点类型
            .withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
            .forPath(nodePath, data);
}

public enum CreateMode {
    // 永久节点
    PERSISTENT (0, false, false),
    //永久有序节点
    PERSISTENT_SEQUENTIAL (2, false, true),
    // 临时节点
    EPHEMERAL (1, true, false),
    // 临时有序节点
    EPHEMERAL_SEQUENTIAL (3, true, true);
    ....
}

@Test
public void getNode() throws Exception {
    Stat stat = new Stat();
    byte[] data = client.getData().storingStatIn(stat).forPath(nodePath);
    System.out.println("节点数据:" + new String(data));
    System.out.println("节点信息:" + stat.toString());
}

public class Stat implements Record {
    private long czxid;
    private long mzxid;
    private long ctime;
    private long mtime;
    private int version;
    private int cversion;
    private int aversion;
    private long ephemeralOwner;
    private int dataLength;
    private int numChildren;
    private long pzxid;
    ...
}

@Test
public void getChildrenNodes() throws Exception {
    List<String> childNodes = client.getChildren().forPath("/hadoop");
    for (String s : childNodes) {
        System.out.println(s);
    }
}

@Test
public void updateNode() throws Exception {
    byte[] newData = "defg".getBytes();
    client.setData().withVersion(0)     // 传入版本号，如果版本号错误则拒绝更新操作,并抛出 BadVersion 异常
            .forPath(nodePath, newData);
}

@Test
public void deleteNodes() throws Exception {
    client.delete()
            .guaranteed()                // 如果删除失败，那么在会继续执行，直到成功
            .deletingChildrenIfNeeded()  // 如果有子节点，则递归删除
            .withVersion(0)              // 传入版本号，如果版本号错误则拒绝删除操作,并抛出 BadVersion 异常
            .forPath(nodePath);
}

@Test
public void existNode() throws Exception {
    // 如果节点存在则返回其状态信息如果不存在则为 null
    Stat stat = client.checkExists().forPath(nodePath + "aa/bb/cc");
    System.out.println("节点是否存在:" + !(stat == null));
}

@Test
public void DisposableWatch() throws Exception {
    client.getData().usingWatcher(new CuratorWatcher() {
        public void process(WatchedEvent event) {
            System.out.println("节点" + event.getPath() + "发生了事件:" + event.getType());
        }
    }).forPath(nodePath);
    Thread.sleep(1000 * 1000);  //休眠以观察测试效果
}

@Test
public void permanentWatch() throws Exception {
    // 使用 NodeCache 包装节点，对其注册的监听作用于节点，且是永久性的
    NodeCache nodeCache = new NodeCache(client, nodePath);
    // 通常设置为 true, 代表创建 nodeCache 时,就去获取对应节点的值并缓存
    nodeCache.start(true);
    nodeCache.getListenable().addListener(new NodeCacheListener() {
        public void nodeChanged() {
            ChildData currentData = nodeCache.getCurrentData();
            if (currentData != null) {
                System.out.println("节点路径：" + currentData.getPath() +
                        "数据：" + new String(currentData.getData()));
            }
        }
    });
    Thread.sleep(1000 * 1000);  //休眠以观察测试效果
}

@Test
public void permanentChildrenNodesWatch() throws Exception {

    // 第三个参数代表除了节点状态外，是否还缓存节点内容
    PathChildrenCache childrenCache = new PathChildrenCache(client, "/hadoop", true);
    /*
         * StartMode 代表初始化方式:
         *    NORMAL: 异步初始化
         *    BUILD_INITIAL_CACHE: 同步初始化
         *    POST_INITIALIZED_EVENT: 异步并通知,初始化之后会触发 INITIALIZED 事件
         */
    childrenCache.start(StartMode.POST_INITIALIZED_EVENT);

    List<ChildData> childDataList = childrenCache.getCurrentData();
    System.out.println("当前数据节点的子节点列表：");
    childDataList.forEach(x -> System.out.println(x.getPath()));

    childrenCache.getListenable().addListener(new PathChildrenCacheListener() {
        public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) {
            switch (event.getType()) {
                case INITIALIZED:
                System.out.println("childrenCache 初始化完成");
                break;
                case CHILD_ADDED:
                // 需要注意的是: 即使是之前已经存在的子节点，也会触发该监听，因为会把该子节点加入 childrenCache 缓存中
                System.out.println("增加子节点:" + event.getData().getPath());
                break;
                case CHILD_REMOVED:
                System.out.println("删除子节点:" + event.getData().getPath());
                break;
                case CHILD_UPDATED:
                System.out.println("被修改的子节点的路径:" + event.getData().getPath());
                System.out.println("修改后的数据:" + new String(event.getData().getData()));
                break;
            }
        }
    });
    Thread.sleep(1000 * 1000); //休眠以观察测试效果
}