依賴

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.apache.logging.log4j</groupId>
        <
 
artifactId>log4j-core</artifactId>
        <version>2.8.2</version>
    </dependency>
    <dependency>
        <groupId>org.apache.zookeeper</groupId>
        <artifactId>zookeeper</artifactId>
        <version>3.4.10</version>
    </dependency
 
>
</dependencies>

一些api的demo：

public class TestZookeeper {

    // 2181 : 訪問 zookeeper叢集的埠號
    private String connectString = "172.20.10.14:2181,172.20.10.4:2181,172.20.10.5:2181";
    private int sessionTimeout = 2000;
    private ZooKeeper zkClient;

    @Before
    public void init() throws IOException {
         zkClient 
 
= new ZooKeeper(connectString, 2000, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }

    //建立節點
    @Test
    public void create() throws Exception {

        // 引數1：要建立的節點的路徑；
        // 引數2：節點資料 ；
        // 引數3：節點許可權 ；
        // 引數4：節點的型別
        String nodeCreated = zkClient.create("/atguigu", "jinlian".getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        System.out.println(nodeCreated);
    }


    //建立子節點並監控資料的變化
    @Test
    public void getDataAndWatch() throws Exception {
        List<String> children = zkClient.getChildren("/", false);

        for (String s:children){
            System.out.println(s);
        }

    }

    // 判斷znode是否存在
    @Test
    public void exist() throws Exception {

        Stat stat = zkClient.exists("/sanguo", false);

        System.out.println(stat == null ? "not exist" : "exist");
    }
}

【案例】伺服器動態節點上下線

需求：

某分散式系統中，主節點可以有多臺，可以動態上下線，任意一臺客戶端都能實時

感受到主伺服器節點的上下線

過程：

程式碼實現

伺服器端：將自己的資訊註冊到zookeeper

public class DistributeServer {

    // 2181 : 訪問 zookeeper叢集的埠號
    private String connectString = "172.20.10.14:2181,172.20.10.4:2181,172.20.10.5:2181";
    private int sessionTimeout = 2000;
    private ZooKeeper zkClient;

    // 獲取與zookeeper叢集的連線
    private void getConnect() throws IOException {
        zkClient = new ZooKeeper(connectString, 2000, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }


    private void regist(String hostName) throws Exception {
        String path = zkClient.create("/servers/server", hostName.getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println(hostName + " is on line!");

    }

    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE); //保證此程序不結束
    }

    public static void main(String[] args) throws Exception {

        //1.連線伺服器叢集
        DistributeServer server = new DistributeServer();
        server.getConnect();
        //2.註冊節點
        server.regist(args[0]);

        //3 業務邏輯
        server.business();
    }
}

客戶端：監聽zookeeper某個節點下，子節點的變化資訊

public class DistrubuteClient {

    // 2181 : 訪問 zookeeper叢集的埠號
    private String connectString = "172.20.10.14:2181,172.20.10.4:2181,172.20.10.5:2181";
    private int sessionTimeout = 2000;
    private ZooKeeper zkClient;

    // 獲取與zookeeper叢集的連線
    private void getConnect() throws IOException {
        zkClient = new ZooKeeper(connectString, 2000, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                try {
                    getChildren();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    private void getChildren() throws Exception {
        List<String> children = zkClient.getChildren("/servers", true);
        //儲存伺服器節點主機名稱的集合
        ArrayList<String> list = new ArrayList<>();
        for(String child:children){
            byte[] data = zkClient.getData("/servers/" + child, false, null);
            list.add(new String(data ));
        }
        //將所有主機名稱線上列印
        System.out.println(list);
    }

    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE); //保證此程序不結束
    }

    public static void main(String[] args) throws Exception {
        DistrubuteClient client =new DistrubuteClient();
        // 獲取連線
        client.getConnect();
        //2.註冊監聽
        client.getChildren();

        client.business();
    }
}

這樣客戶端就能動態的監視服務端主機的變化情況