零、创建 SpringBoot 项目

https://start.aliyun.com

Lombok
SpringWeb

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>2.2.2.RELEASE</version>
            </plugin>
        </plugins>
    </build>

一、Java 客户端（MAVEN 依赖）

(1) ZooKeeper 自带的客户端

<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.6.0</version>
</dependency>

(2) Apache 的开源客户端 Curator

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-framework</artifactId>
    <version>4.3.0</version>
</dependency>
<dependency>
    <groupId>org.apache.curator</groupId>
    <artifactId>curator-client</artifactId>
    <version>4.3.0</version>
</dependency>

(3) Apache 开源的 zkclient（旧）

<dependency>
    <groupId>com.101tec</groupId>
    <artifactId>zkclient</artifactId>
    <version>0.11</version>
</dependency>

二、Java 客户端 API

(1) 创建 Java 与 ZooKeeper 的连接会话

创建 ZooKeeper 对象，放入 IoC 容器即可。

① Java 代码

@Configuration
public class ZooKeeperClient {
    // 要连接的 ZooKeeper 所在的服务器地址和端口号, 多个服务器地址用【逗号】分隔
    private static final String CONNECT_STRING = "192.168.80.128:2888:3888,192.168.80.128:2888:3888,192.168.80.128:2889:3889";
    // 会话超时时间 (单位: 毫秒)
    private static final int SESSION_TIMEOUT = 30000; // 30s

    @Bean
    public ZooKeeper zooKeeper() throws Exception {
        return new ZooKeeper(CONNECT_STRING, SESSION_TIMEOUT, new Watcher() {
            public void process(WatchedEvent event) {
                System.out.println("event = " + event);
                if (event.getState() == Event.KeeperState.SyncConnected) {
                    System.out.println("Java 连接 ZooKeeper 成功!");
                }
            }
        });
    }

}

② 若无法连接成功

若无法连接成功，尝试关闭防火墙。

③ Linux 防火墙相关命令

a. 启动防火墙

systemctl start firewalld  

b. 关闭防火墙

systemctl stop firewalld

c. 关闭防火墙

systemctl stop firewalld

d. 重启防火墙

firewall-cmd --reload

e. 查看防火墙状态

systemctl status firewalld

(2) 创建节点

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;

    /**
     * 创建节点
     *
     * @param path     路径
     * @param data     数据
     * @param nodeType 节点类型
     *                 (常用取值: PERSISTENT、PERSISTENT_SEQUENTIAL、EPHEMERAL、EPHEMERAL_SEQUENTIAL)
     * @return 新创建的节点的路径
     */
    @PostMapping("/create")
    public String create(String path, String data, String nodeType) throws Exception {
        return zooKeeper.create(path,
                data.getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.valueOf(nodeType));
    }

}

(3) 获取节点中的数据

① 同步获取

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;

    /**
     * 同步获取指定节点下的数据
     */
    @GetMapping("/get")
    public String get(String path) throws Exception {
        return path + " 节点下的数据: " +
                new String(zooKeeper.getData(path, false,
                        getStatVersionInfo(path)));
    }

    /**
     * 查询指定路径的节点的状态(版本)信息 (版本不存在返回 null)
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    }

}

② 异步回调

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;

    /**
     * 异步获取指定节点下的数据
     */
    @GetMapping("/getAsync")
    public String getAsync(String path) throws Exception {
        String statString = getStatVersionInfo(path).toString();

        zooKeeper.getData(path, false, new AsyncCallback.DataCallback() {
            public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) {
                System.out.println("数据：" + new String(data));
                System.out.println("context：" + ctx);
            }
        }, path + "_" + statString);

        return "获取 " + path + " 路径(节点)下的数据";
    }

    /**
     * 查询指定路径的节点的状态(版本)信息 (版本不存在返回 null)
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    }

}

③ 获取子节点列表

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;

    /**
     * 获取指定路径下的子节点列表
     */
    @GetMapping("/listChildNodes")
    public List<String> listChildNodes(String path) throws Exception {
        return zooKeeper.getChildren(path, false);
    }
    
}

(4) 删除节点

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;
     
    /**
     * 删除节点
     */
    @PostMapping("/delete")
    public String delete(String path) throws Exception {
        Stat statVersionInfo = getStatVersionInfo(path);
        if (statVersionInfo == null) return "节点不存在";

        zooKeeper.delete(path, statVersionInfo.getVersion());
        return getStatVersionInfo(path) == null ? "删除成功" : "删除失败";
    } 

    /**
     * 查询指定路径的节点的状态(版本)信息
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    }

}

(5) 更新数据

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper; 

    /**
     * 同步获取指定节点下的数据
     */
    @GetMapping("/get")
    public String get(String path) throws Exception {
        return path + " 节点下的数据: " +
                new String(zooKeeper.getData(path, false,
                        getStatVersionInfo(path)));
    }  

    /**
     * 更新节点数据
     */
    @PostMapping("/updateNodeData")
    public Map<String, String> updateNodeData(String path, String data) throws Exception {
        Map<String, String> resMap = new HashMap<>();

        Stat oldStat = getStatVersionInfo(path);
        if (oldStat == null) {
            resMap.put("msg", "节点不存在");
            return resMap;
        }

        // 查询节点数据
        String curNodeData = get(path);

        Stat stat = zooKeeper.setData(path, data.getBytes(), oldStat.getVersion());

        if (oldStat.getVersion() != stat.getVersion()) {
            resMap.put("msg", "更新节点数据成功");
            resMap.put("oldData", curNodeData);
            resMap.put("newData", data);
        } else {
            resMap.put("msg", "更新节点数据失败");
        }
        return resMap;

    } 

    /**
     * 查询指定路径的节点的状态(版本)信息
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    }

}

(6) 事件处理

ZooKeeper 中的 get 命令可查看节点中存储的数据，并绑定【节点数据改变事件】（是一次性事件）
ZooKeeper 中的 list 命令可查看子节点列表，并绑定【节点改变事件】（是一次性事件）

① 绑定一次性事件

a. 获取节点数据绑定的节点改变事件

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper; 
    
    /**
     * 查询指定路径的节点的状态(版本)信息
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    }

    /**
     * 获取节点数据绑定的一次性节点数据改变事件【NodeDataChanged】
     */
    @GetMapping("/addWatchByGet")
    public String addWatchByGet(String path) throws Exception {
        Stat statVersion = getStatVersionInfo(path);
        if (statVersion == null) return "节点不存在";

        zooKeeper.getData(path, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println("【addWatchByGet】触发节点类型：" + event.getType());
            }
        }, statVersion);
        return "获取节点数据绑定的一次性节点数据改变事件";
    }

}

b. 获取子节点列表绑定的子节点改变事件

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper; 
    
    /**
     * 查询指定路径的节点的状态(版本)信息
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    } 

    /**
     * 获取子节点列表绑定的一次性子节点改变事件【NodeChildrenChanged】
     */
    @GetMapping("/addWatchByGetChildren")
    public String addWatchByGetChildren(String path) throws Exception {
        Stat statVersion = getStatVersionInfo(path);
        if (statVersion == null) return "节点不存在";

        zooKeeper.getChildren(path, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                System.out.println("【addWatchByGetChildren】触发节点类型：" + event.getType());
            }
        });

        return "获取子节点列表绑定的一次性子节点改变事件";
    }

}

② 绑定永久事件

监听当前节点的数据改变和当前节点（路径）的子节点的创建和删除，子节点数据发生改变不会触发事件监听。

@RestController
@RequestMapping("/zookeepers")
public class ZookeeperController {

    @Autowired
    private ZooKeeper zooKeeper;
    
    /**
     * 查询指定路径的节点的状态(版本)信息
     */
    public Stat getStatVersionInfo(String path) throws Exception {
        return zooKeeper.exists(path, false);
    } 
    
    /**
     * 给指定路径（节点）绑定永久事件 (1. 子节点改变事件; 2. 节点数据改变事件)
     */
    @PostMapping("/addWatch")
    public String addWatch(String path) throws Exception {
        Stat statVersion = getStatVersionInfo(path);
        if (statVersion == null) return "节点不存在";

        zooKeeper.addWatch(path, new Watcher() {
            @Override
            public void process(WatchedEvent event) {
                Event.EventType eventType = event.getType();
                if (eventType == Event.EventType.NodeChildrenChanged) {
                    System.out.println("触发了子节点改变事件");
                    // 重新获取子节点列表的代码
                } else if (eventType == Event.EventType.NodeDataChanged) {
                    System.out.println("触发了 NodeDataChanged");
                    // 重新获取节点数据的代码
                }
            }
        }, AddWatchMode.PERSISTENT);

        return "绑定永久事件";
    }

}

③ 递归绑定事件

• 给当前节点及其子节点都绑定节点改变事件和节点数据改变事件
• 与绑定永久事件的代码的不同点是 addWatch 的最后一个参数不一样，绑定永久事件的最后一个参数是 AddWatchMode.PERSISTENT，递归绑定永久事件的最后一个参数是 AddWatchMode.PERSISTENT_RECURSIVE