ZooKeeper客户端Curator（监听篇）
maven依赖
<dependency>
<groupId>org.apache.curator</groupId>
<artifactId>curator-recipes</artifactId>
<version>2.8.0</version>
</dependency>
Path Cache
Path Cache用来监控一个ZNode的子节点. 当一个子节点增加， 更新，删除时， Path Cache会改变它的状态， 会包含最新的子节点， 子节点的数据和状态。（此处需要注意，他只会监听一级子节点，不会循环监听子节点下面的child）
实际使用时会涉及到四个类：
PathChildrenCache
PathChildrenCacheEvent
PathChildrenCacheListener
ChildData
创建Path Cache
通过下面的构造函数创建Path Cache:
public PathChildrenCache(CuratorFramework client, String path, boolean cacheData, boolean dataIsCompressed, final ExecutorService executorService)
想使用cache，必须调用它的start方法，不用之后调用close方法。
start有两个， 其中一个可以传入StartMode，用来为初始的cache设置暖场方式(warm)：
个人建议使用此构造方法，ExecutorService使用自己构建的线程池，保证线程可控
添加监控节点状态
添加监控节点状态的改变的Listener时，建议使用此方法，手动传入我们构建的线程池，保证线程可控。
childrenCache.getListenable().(T listener, Executor executor)；
为什么要自己传入线程池呢？看下图和源码
public PathChildrenCache(CuratorFramework client, String path, boolean cacheData)
{
this(client, path, cacheData, false, new CloseableExecutorService(Executors.newSingleThreadExecutor(defaultThreadFactory), true));
}
public void addListener(T listener)
{
addListener(listener, MoreExecutors.sameThreadExecutor());
}
因为在zk丢失链接的时候，默认不传线程池的方法，在每次重连时都会会新new 出来一个线程池，线程一直处于活跃状态，如果zk服务端长时间未能恢复，会导致客户端现成打满
设置/更新、移除
设置/更新、移除其实是使用client (CuratorFramework)来操作, 不通过PathChildrenCache操作：
client.setData().forPath(path, bytes); client.create().creatingParentsIfNeeded().forPath(path, bytes); client.delete().forPath(path);
而查询缓存使用下面的方法：
for (ChildData data : cache.getCurrentData()) {
System.out.println(data.getPath() + " = " + new String(data.getData()));
}
最后附上一段完整的代码
import java.util.concurrent.CountDownLatch; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.ThreadPoolExecutor; import java.util.concurrent.TimeUnit; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.PathChildrenCache; import org.apache.curator.retry.ExponentialBackoffRetry; /** * ZKClient * * @author jiangzhixiong * @email [email protected] * @date 2015年10月12日 下午5:18:21 */ public class ChildPathZkClient { // ip和端口url private String url; // 需要监听的base path private String basePath; private static CuratorFramework client = null; private final static ThreadPoolExecutor executor = new ThreadPoolExecutor(20, 100, 5l, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(100), new ThreadPoolExecutor.CallerRunsPolicy()); public void init() throws Throwable { if (basePath == null) { basePath = "o2o/zk/cache"; } client = CuratorFrameworkFactory.builder().namespace(basePath).connectString(url).sessionTimeoutMs(5000).connectionTimeoutMs(3000).retryPolicy(new ExponentialBackoffRetry(1000, 0)).build(); client.start(); /** * 监听子节点的变化情况 */ watchChild("/"); } protected static void watchChild(String path) throws Exception { PathChildrenCache childrenCache = new PathChildrenCache(client, path, true, false, executor); ZkPathListener listener = new ZkPathListener(); listener.setPathChildrenCache(childrenCache); childrenCache.getListenable().addListener(listener, executor); childrenCache.start(); } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public String getBasePath() { return basePath; } public void setBasePath(String basePath) { this.basePath = basePath; } public static void main(String[] args) throws Throwable { CountDownLatch latch = new CountDownLatch(1); client = CuratorFrameworkFactory.builder().namespace("o2o/zk/cache").connectString("192.168.200.98:2181").sessionTimeoutMs(5000).connectionTimeoutMs(3000) .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); /** * 监听子节点的变化情况 */ watchChild("/"); latch.await(); } }
import java.util.Map; import org.apache.commons.lang3.StringUtils; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.recipes.cache.PathChildrenCache; import org.apache.curator.framework.recipes.cache.PathChildrenCacheEvent; import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener; import org.apache.logging.log4j.Level; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.apache.logging.log4j.core.LoggerContext; import org.apache.logging.log4j.core.config.Configuration; import org.apache.logging.log4j.core.config.LoggerConfig; import com.jd.o2o.web.product.constants.zk.ZkSwitchEnum; import com.jd.o2o.web.product.constants.zk.ZkValueEnum; import com.jd.o2o.zk.cache.serializer.ZooKeeperSerializer; import com.jd.o2o.zk.cache.serializer.impl.JdkSerializationZooKeeperSerializer; /** * ZK监听器 * * @author jiangzhixiong * @email [email protected] * @date 2015年10月12日 下午5:18:38 */ public class ZkPathListener implements PathChildrenCacheListener { private final Logger logger = LogManager.getLogger(ZkPathListener .class); private final ZooKeeperSerializer<?> defaultSerializer = new JdkSerializationZooKeeperSerializer(); private PathChildrenCache pathChildrenCache; @Override public void childEvent(CuratorFramework paramCuratorFramework, PathChildrenCacheEvent event) throws Exception { switch (event.getType()) { case CHILD_ADDED: // TODO System.out.println(defaultSerializer.deserialize(event.getData().getData())); break; case CHILD_UPDATED: // TODO System.out.println(defaultSerializer.deserialize(event.getData().getData())); break; case CHILD_REMOVED: // TODO System.out.println(defaultSerializer.deserialize(event.getData().getData())); break; default: break; } } }
Node Cache
Node Cache用来监控一个ZNode. 当节点的数据修改或者删除时，Node Cache能更新它的状态包含最新的改变。
涉及到下面的三个类：
NodeCache
NodeCacheListener
ChildData
构建NodeCache
public NodeCache(CuratorFramework client, String path)
想使用cache，依然要调用它的start方法，不用之后调用close方法。
添加监控节点状态
添加监控节点状态的改变的Listener时，建议使用此方法，手动传入我们构建的线程池，保证线程可控。
NodeCache.getListenable().(T listener, Executor executor)；
同样附一段完整的代码
import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.NodeCache; import org.apache.curator.framework.recipes.cache.NodeCacheListener; import org.apache.curator.retry.ExponentialBackoffRetry; /** * ZK链接 * * @author jiangzhixiong * @email [email protected] * @date 2015年10月12日 下午5:18:21 */ public class ZkNodeClient { // ip和端口url private String url; // 需要监听的base path private String basePath; private static NodeCache nodeCache; private static CuratorFramework client = null; private final static ExecutorService EXECUTOR_SERVICE = Executors.newSingleThreadExecutor(); public void init() throws Throwable { if (basePath == null) { basePath = "o2o/zk/cache"; } client = CuratorFrameworkFactory.builder().namespace(basePath).connectString(url).sessionTimeoutMs(5000).connectionTimeoutMs(3000).retryPolicy(new ExponentialBackoffRetry(1000, 0)).build(); client.start(); nodeCache = new NodeCache(client, "/"); /** * 监听子节点的变化情况 */ watchChild(); } protected static void watchChild() throws Exception { nodeCache.getListenable().addListener(new NodeCacheListener() { @Override public void nodeChanged() throws Exception { System.out.println(nodeCache.getCurrentData().getPath() + ":" + nodeCache.getCurrentData().getData()); } }, EXECUTOR_SERVICE); nodeCache.start(); } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public String getBasePath() { return basePath; } public void setBasePath(String basePath) { this.basePath = basePath; } public static void main(String[] args) throws Throwable { CountDownLatch latch = new CountDownLatch(1); client = CuratorFrameworkFactory.builder().namespace("o2o/zk/cache").connectString("192.168.200.98:2181").sessionTimeoutMs(5000).connectionTimeoutMs(3000) .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build(); client.start(); /** * 监听子节点的变化情况 */ watchChild("/"); latch.await(); } }
Tree Node
这种类型的即可以监控节点的状态，还监控节点的子节点的状态， 类似上面两种cache的组合。 这也就是Tree的概念。 它监控整个树中节点的状态。（只要是所监听的路径下的所有叶子节点都会监听）
涉及到下面四个类。
TreeCache
TreeCacheListener
TreeCacheEvent
ChildData
构造TreeCache
而关键的TreeCache的构造函数为
public TreeCache(CuratorFramework client, String path)
添加监控节点状态
添加监控节点状态的改变的Listener时，建议使用此方法，手动传入我们构建的线程池，保证线程可控。
TreeCache.getListenable().(T listener, Executor executor)；
想使用cache，依然要调用它的start方法，不用之后调用close方法。
getCurrentChildren()返回cache的状态，类型为Map。 而getCurrentData()返回监控的path的数据。
最后同样附一段完整代码
import java.util.concurrent.CountDownLatch; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.CuratorFrameworkFactory; import org.apache.curator.framework.recipes.cache.TreeCache; import org.apache.curator.retry.ExponentialBackoffRetry; /** * ZK链接 * * @author jiangzhixiong * @email [email protected] * @date 2015年10月12日 下午5:18:21 */ public class TreeClient { // ip和端口url private String url; // 需要监听的base path private String basePath; private static CuratorFramework client = null; private static TreeCache cache = null; private static ZkTreeListener listener = new ZkTreeListener(); private static ExecutorService executorService = Executors.newSingleThreadExecutor(); public void init() throws Throwable { if (basePath == null) { basePath = "o2o/zk/cache"; } // 修改重连次数，使用最初的线程进行重连监听，不重新新建线程 ExponentialBackoffRetry(1000, 0) client = CuratorFrameworkFactory.builder().namespace(basePath).connectString(url).sessionTimeoutMs(5000).connectionTimeoutMs(3000).retryPolicy(new ExponentialBackoffRetry(1000, 10)).build(); client.start(); /** * 监听子节点的变化情况 */ watchChild("/product"); watchChild("/switch"); } protected static void watchChild(String path) throws Exception { // 改用TreeCacheListener，免除循环监听子节点的问题 cache = new TreeCache(client, path); cache.getListenable().addListener(listener, executorService); cache.start(); } public String getUrl() { return url; } public void setUrl(String url) { this.url = url; } public String getBasePath() { return basePath; } public void setBasePath(String basePath) { this.basePath = basePath; } public static void main(String[] args) throws Throwable { CountDownLatch latch = new CountDownLatch(1); client = CuratorFrameworkFactory.builder().namespace("o2o/zk/cache").connectString("192.168.200.98:2181").sessionTimeoutMs(5000).connectionTimeoutMs(3000) .retryPolicy(new ExponentialBackoffRetry(1000, 0)).build(); client.start(); /** * 监听子节点的变化情况 */ watchChild("/product"); watchChild("/switch"); latch.await(); } }
import java.util.Map; import org.apache.commons.lang3.StringUtils; import org.apache.curator.framework.CuratorFramework; import org.apache.curator.framework.recipes.cache.PathChildrenCacheListener; import org.apache.curator.framework.recipes.cache.TreeCacheEvent; import org.apache.curator.framework.recipes.cache.TreeCacheListener; import org.apache.logging.log4j.Level; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; import org.apache.logging.log4j.core.LoggerContext; import org.apache.logging.log4j.core.config.Configuration; import org.apache.logging.log4j.core.config.LoggerConfig; import com.jd.o2o.web.product.constants.zk.ZkSwitchEnum; import com.jd.o2o.web.product.constants.zk.ZkValueEnum; import com.jd.o2o.zk.cache.serializer.ZooKeeperSerializer; import com.jd.o2o.zk.cache.serializer.impl.JdkSerializationZooKeeperSerializer; /** * TreeCache ZK监听器 * * @author jiangzhixiong * @email [email protected] * @date 2015年10月12日 下午5:18:38 */ public class ZkTreeListener implements TreeCacheListener { private final Logger logger = LogManager.getLogger(TreeCacheListener .class); private final ZooKeeperSerializer<?> defaultSerializer = new JdkSerializationZooKeeperSerializer(); @Override public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception { System.out.println(event.getData().getPath()); switch (event.getType()) { case NODE_ADDED: if (event.getData().getData() == null) { break; } //TODO break; case NODE_UPDATED: if (event.getData().getData() == null) { break; } //TODO break; default: break; } } }