zookeepr监听器和api应用(高级)

原创
2017/03/08 23:21
阅读数 137

##Zookeeper的监听器工作机制

监听器是一个接口,我们的代码中可以实现Wather这个接口,实现其中的process方法,方法中即我们自己的业务逻辑
监听器的注册是在获取数据的操作中实现:
getData(path,watch?)监听的事件是:节点数据变化事件
getChildren(path,watch?)监听的事件是:节点下的子节点增减变化事件

#zookeeper应用案例(分布式应用HA||分布式锁) ##1 实现分布式应用的(主节点HA)及客户端动态更新主节点状态 某分布式系统中,主节点可以有多台,可以动态上下线
任意一台客户端都能实时感知到主节点服务器的上下线

###A、客户端实现 public class AppClient { private String groupNode = "sgroup"; private ZooKeeper zk; private Stat stat = new Stat(); private volatile List<String> serverList;

	/**
	 * 连接zookeeper
	 */
	public void connectZookeeper() throws Exception {
		zk 
= new ZooKeeper("localhost:4180,localhost:4181,localhost:4182", 5000, new Watcher() {
			public void process(WatchedEvent event) {
				// 如果发生了"/sgroup"节点下的子节点变化事件, 更新server列表, 并重新注册监听
				if (event.getType() == EventType.NodeChildrenChanged 
					&& ("/" + groupNode).equals(event.getPath())) {
					try {
						updateServerList();
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			}
		});

		updateServerList();
	}

	/**
	 * 更新server列表
	 */
	private void updateServerList() throws Exception {
		List<String> newServerList = new ArrayList<String>();

		// 获取并监听groupNode的子节点变化
		// watch参数为true, 表示监听子节点变化事件. 
		// 每次都需要重新注册监听, 因为一次注册, 只能监听一次事件, 如果还想继续保持监听, 必须重新注册
		List<String> subList = zk.getChildren("/" + groupNode, true);
		for (String subNode : subList) {
			// 获取每个子节点下关联的server地址
			byte[] data = zk.getData("/" + groupNode + "/" + subNode, false, stat);
			newServerList.add(new String(data, "utf-8"));
		}

		// 替换server列表
		serverList = newServerList;

		System.out.println("server list updated: " + serverList);
	}

	/**
	 * client的工作逻辑写在这个方法中
	 * 此处不做任何处理, 只让client sleep
	 */
	public void handle() throws InterruptedException {
		Thread.sleep(Long.MAX_VALUE);
	}

	public static void main(String[] args) throws Exception {
		AppClient ac = new AppClient();
		ac.connectZookeeper();

		ac.handle();
	}
}

###B、服务器端实现 public class AppServer { private String groupNode = "sgroup"; private String subNode = "sub";

	/**
	 * 连接zookeeper
	 * [@param](https://my.oschina.net/u/2303379) address server的地址
	 */
	public void connectZookeeper(String address) throws Exception {
		ZooKeeper zk = new ZooKeeper(
"localhost:4180,localhost:4181,localhost:4182", 
5000, new Watcher() {
			public void process(WatchedEvent event) {
				// 不做处理
			}
		});
		// 在"/sgroup"下创建子节点
		// 子节点的类型设置为EPHEMERAL_SEQUENTIAL, 表明这是一个临时节点, 且在子节点的名称后面加上一串数字后缀
		// 将server的地址数据关联到新创建的子节点上
		String createdPath = zk.create("/" + groupNode + "/" + subNode, address.getBytes("utf-8"), 
			Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
		System.out.println("create: " + createdPath);
	}
	
	/**
	 * server的工作逻辑写在这个方法中
	 * 此处不做任何处理, 只让server sleep
	 */
	public void handle() throws InterruptedException {
		Thread.sleep(Long.MAX_VALUE);
	}
	
	public static void main(String[] args) throws Exception {
		// 在参数中指定server的地址
		if (args.length == 0) {
			System.err.println("The first argument must be server address");
			System.exit(1);
		}
		
		AppServer as = new AppServer();
		as.connectZookeeper(args[0]);
		as.handle();
	}
}

##2分布式共享锁的简单实现 ###客户端A public class DistributedClient { // 超时时间 private static final int SESSION_TIMEOUT = 5000; // zookeeper server列表 private String hosts = "localhost:4180,localhost:4181,localhost:4182"; private String groupNode = "locks"; private String subNode = "sub";

    private ZooKeeper zk;
    // 当前client创建的子节点
    private String thisPath;
    // 当前client等待的子节点
    private String waitPath;

    private CountDownLatch latch = new CountDownLatch(1);

    /**
     * 连接zookeeper
     */
    public void connectZookeeper() throws Exception {
        zk = new ZooKeeper(hosts, SESSION_TIMEOUT, new Watcher() {
            public void process(WatchedEvent event) {
                try {
                    // 连接建立时, 打开latch, 唤醒wait在该latch上的线程
                    if (event.getState() == KeeperState.SyncConnected) {
                        latch.countDown();
                    }

                    // 发生了waitPath的删除事件
                    if (event.getType() == EventType.NodeDeleted && event.getPath().equals(waitPath)) {
                        doSomething();
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        // 等待连接建立
        latch.await();

        // 创建子节点
        thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL_SEQUENTIAL);

        // wait一小会, 让结果更清晰一些
        Thread.sleep(10);

        // 注意, 没有必要监听"/locks"的子节点的变化情况
        List<String> childrenNodes = zk.getChildren("/" + groupNode, false);

        // 列表中只有一个子节点, 那肯定就是thisPath, 说明client获得锁
        if (childrenNodes.size() == 1) {
            doSomething();
        } else {
            String thisNode = thisPath.substring(("/" + groupNode + "/").length());
            // 排序
            Collections.sort(childrenNodes);
            int index = childrenNodes.indexOf(thisNode);
            if (index == -1) {
                // never happened
            } else if (index == 0) {
                // inddx == 0, 说明thisNode在列表中最小, 当前client获得锁
                doSomething();
            } else {
                // 获得排名比thisPath前1位的节点
                this.waitPath = "/" + groupNode + "/" + childrenNodes.get(index - 1);
                // 在waitPath上注册监听器, 当waitPath被删除时, zookeeper会回调监听器的process方法
                zk.getData(waitPath, true, new Stat());
            }
        }
    }

    private void doSomething() throws Exception {
        try {
            System.out.println("gain lock: " + thisPath);
            Thread.sleep(2000);
            // do something
        } finally {
            System.out.println("finished: " + thisPath);
            // 将thisPath删除, 监听thisPath的client将获得通知
            // 相当于释放锁
            zk.delete(this.thisPath, -1);
        }
    }

    public static void main(String[] args) throws Exception {
        for (int i = 0; i < 10; i++) {
            new Thread() {
                public void run() {
                    try {
                        DistributedClient dl = new DistributedClient();
                        dl.connectZookeeper();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }.start();
        }

        Thread.sleep(Long.MAX_VALUE);
    }
}

##分布式多进程模式实现:

public class DistributedClientMy {
	

	// 超时时间
	private static final int SESSION_TIMEOUT = 5000;
	// zookeeper server列表
	private String hosts = "spark01:2181,spark02:2181,spark03:2181";
	private String groupNode = "locks";
	private String subNode = "sub";
	private boolean haveLock = false;

	private ZooKeeper zk;
	// 当前client创建的子节点
	private volatile String thisPath;

	/**
	 * 连接zookeeper
	 */
	public void connectZookeeper() throws Exception {
		zk = new ZooKeeper("spark01:2181", SESSION_TIMEOUT, new Watcher() {
			public void process(WatchedEvent event) {
				try {

					// 子节点发生变化
					if (event.getType() == EventType.NodeChildrenChanged && event.getPath().equals("/" + groupNode)) {
						// thisPath是否是列表中的最小节点
						List<String> childrenNodes = zk.getChildren("/" + groupNode, true);
						String thisNode = thisPath.substring(("/" + groupNode + "/").length());
						// 排序
						Collections.sort(childrenNodes);
						if (childrenNodes.indexOf(thisNode) == 0) {
							doSomething();
							thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
									CreateMode.EPHEMERAL_SEQUENTIAL);
						}
					}
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});

		// 创建子节点
		thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
				CreateMode.EPHEMERAL_SEQUENTIAL);

		// wait一小会, 让结果更清晰一些
		Thread.sleep(new Random().nextInt(1000));

		// 监听子节点的变化
		List<String> childrenNodes = zk.getChildren("/" + groupNode, true);

		// 列表中只有一个子节点, 那肯定就是thisPath, 说明client获得锁
		if (childrenNodes.size() == 1) {
			doSomething();
			thisPath = zk.create("/" + groupNode + "/" + subNode, null, Ids.OPEN_ACL_UNSAFE,
					CreateMode.EPHEMERAL_SEQUENTIAL);
		}
	}

	/**
	 * 共享资源的访问逻辑写在这个方法中
	 */
	private void doSomething() throws Exception {
		try {
			System.out.println("gain lock: " + thisPath);
			Thread.sleep(2000);
			// do something
		} finally {
			System.out.println("finished: " + thisPath);
			// 将thisPath删除, 监听thisPath的client将获得通知
			// 相当于释放锁
			zk.delete(this.thisPath, -1);
		}
	}

	public static void main(String[] args) throws Exception {
		DistributedClientMy dl = new DistributedClientMy();
		dl.connectZookeeper();
		Thread.sleep(Long.MAX_VALUE);
	}

	
}

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