一、Curator是NetFlix公司开源的一套Zookeeper客户端框架，其特点如下：
1、连接重连
2、反复注册Watcher
3、NodeExistsException处理
二、常用API
API文档对应地址：http://curator.apache.org/curator-framework/index.html
RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);//Zookeeper每1秒检查一次session状态，如果断掉的话，重新连接，如果连续3次均没连上，则session失效
CuratorFramework client = CuratorFrameworkFactory.newClient(connectingString,sessionTimeout,connectionTimeOut,retryPolicy);
//创建节点
client.create().forPath(path);
//创建节点并设置值
client.create().forPath(path,"init".getBytes());
//创建临时节点
client.create().withMode(CreateMode.EPHEMERAL).forPath(path);
//创建临时节点并递归创建父节点
client.create().creatingParentContainersIfNeeded().withMode(CreateMode.EPHEMERAL).forPath(path);
//删除节点
client.delete().forPath(path);
//删除节点并递归删除其所有子节点
client.delete().deletingChildrenIfNeeded().forPath(path);
//删除节点，强制指定版本进行删除
client.delete().withVersion(version).forPath(path);
//强制保证删除
client.delete().guaranteed().forPath(path);
//获取某个节点数据
client.getData().forPath(path);
//读取一个节点的数据内容，同时按获取到该节点的stat
Stat stat = new Stat();
client.getData().storingStatIn(stat).forPath(path);
//更新一个节点的数据内容
client.setData().withVersion(version).forPath(path);
//异步
client.create().creatingParentsIfNeeded().inBackground(new BackgroundCallback() {
@Override
public void processResult(CuratorFramework curatorFramework, CuratorEvent curatorEvent) throws Exception {
}
}).forPath(path,"init".getBytes());
三、监听器
1、NodeCache:监听节点变化
NodeCache cache = new NodeCache(client,path,false);
cache.start(true); //第一次启动的时候就会从Zookeeper上同步数据
cache.getListenable().addListener(new NodeCacheListener() {
@Override
public void nodeChanged() throws Exception {
System.out.println(cache.getCurrentData().getData());
}
});
2、PathChildrenCache:监控某个节点子节点的变化【无法对父节点以及二级节点数据进行监控】
PathChildrenCache childrenCache = new PathChildrenCache(client,path,true);
childrenCache.start(PathChildrenCache.StartMode.POST_INITIALIZED_EVENT);
childrenCache.getListenable().addListener(new PathChildrenCacheListener() {
@Override
public void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent pathChildrenCacheEvent) throws Exception {
System.out.println("节点变更类型："+pathChildrenCacheEvent.getType()+"对应节点："+pathChildrenCacheEvent.getData().getPath());
}
});
四、LeaderLatch
LeaderLatch⽤于实现Leader的选举
– 触发方法isLeader()，表示成为leader
– 触发notLeader()，表示失去leader权限
– 场景：参考xxx-callback
public void afterPropertiesSet() throws Exception {
if (leaderLatch != null) {
return;
}
leaderLatch = new LeaderLatch(curatorClient,//zk客户端实例
PATH,//选举根节点路径
OSUtils.getServerIp() + "_" + UUID.randomUUID().toString()); //客户端ID，用来标记客户端，即客户端编号，名称
leaderLatch.addListener(new LeaderLatchListener() {
@Override
public void isLeader() { //抢主成功时触发
ContextHolder.setLeader(true);
LOGGER.info("im leader");
}
@Override
public void notLeader() { //抢主失败时触发
ContextHolder.setLeader(false);
LOGGER.info("im not leader");
}
});
leaderLatch.start();
}
五、分布式锁
1、模拟并发
CountDownLatch countDownLatch = new CountDownLatch(1);
for (int i=0;i<10;i++){
new Thread(new Runnable() {
@Override
public void run() {
try {
countDownLatch.await();
}catch (Exception e){
}
System.out.println(System.currentTimeMillis());
}
}).start();
}
countDownLatch.countDown();
2、分布式锁控制
client.start();
String lock_path = "/lock";
final InterProcessMutex lock = new InterProcessMutex(client,lock_path);
CountDownLatch countDownLatch = new CountDownLatch(1);
for (int i=0;i<10;i++){
new Thread(new Runnable() {
@Override
public void run() {
try {
countDownLatch.await();
lock.acquire();
}catch (Exception e){
}
System.out.println(System.currentTimeMillis());
try {
lock.release();
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
}
countDownLatch.countDown();
六、分布式计数器
DistributedAtomicInteger atomicInteger = new DistributedAtomicInteger(client,path,new RetryNTimes(1000,3));
atomicInteger.add(8);
思考：
1、开关同步采用Zookeeper是否可以 ？
2、ABTest？
3、分批任务计算？
4、配置中心