Spring_Spring + Apache Curator 实现分布式应用单节点执行Job

1. Curator的Maven依赖如下，一般直接使用curator-recipes就行了，如果需要自己封装一些底层些的功能的话，例如增加连接管理重试机制等，则可以引入curator-framework包。

<dependency>        <groupId>org.apache.curator</groupId>        <artifactId>curator-recipes</artifactId>        <version>2.7.0</version>    </dependency>

2. spring 新增zookeeper bean 配置

<bean id="selectMasterZookeeper" class="java.lang.String" ><constructor-arg value="10.58.22.191:2181,10.58.22.192:2181,10.58.22.193:2181,10.58.50.149:2181,10.58.50.150:2181" /></bean>

3. 添加主节点选择Util

import java.util.HashMap;import java.util.Map;import javax.annotation.Resource;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.leader.LeaderSelector;import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;import org.apache.curator.retry.ExponentialBackoffRetry;import org.springframework.stereotype.Component;@Componentpublic class SelectMusterUtils {@Resource(name = "selectMasterZookeeper")private String selectMasterZookeeper;Map<String, Boolean> masterMap = new HashMap<String, Boolean>();public void selectMaster (final String leaderPath) {CuratorFramework client = CuratorFrameworkFactory.builder().connectString(selectMasterZookeeper).sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();client.start();@SuppressWarnings("resource")LeaderSelector selector = new LeaderSelector(client, leaderPath,new LeaderSelectorListenerAdapter() {@Overridepublic void takeLeadership(CuratorFramework client) throws Exception {masterMap.put(leaderPath, true);while (true) {Thread.sleep(3000);}}});masterMap.put(leaderPath, false);selector.autoRequeue();selector.start();}public boolean checkMaster (String leaderPath) {Boolean isMaster = masterMap.get(leaderPath);return isMaster == null ? false : isMaster;}}

4.Job类中添加

@PostConstructpublic void selectMaster() {selectMusterUtils.selectMaster(SelectMasterPathEnum.PR_SUPPLIER_PRO_AUTO_MAINTAIN);}

5. Job方法添加spring schedule

@Scheduled(cron="0 0/1 * * * ? ")public void query () {if (selectMusterUtils.checkMaster(SelectMasterPathEnum.PR_SUPPLIER_PRO_AUTO_MAINTAIN)) {//业务逻辑}}

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参考：

1.Curator“菜谱”


既然Maven包叫做curator-recipes，那说明Curator有它独特的“菜谱”：


锁：包括共享锁、共享可重入锁、读写锁等。
选举：Leader选举算法。
Barrier：阻止分布式计算直至某个条件被满足的“栅栏”，可以看做JDK Concurrent包中Barrier的分布式实现。
缓存：前面提到过的三种Cache及监听机制。
持久化结点：连接或Session终止后仍然在Zookeeper中存在的结点。
队列：分布式队列、分布式优先级队列等。
1.1 分布式锁


分布式编程时，比如最容易碰到的情况就是应用程序在线上多机部署，于是当多个应用同时访问某一资源时，就需要某种机制去协调它们。例如，现在一台应用正在rebuild缓存内容，要临时锁住某个区域暂时不让访问；又比如调度程序每次只想一个任务被一台应用执行等等。


下面的程序会启动两个线程t1和t2去争夺锁，拿到锁的线程会占用5秒。运行多次可以观察到，有时是t1先拿到锁而t2等待，有时又会反过来。Curator会用我们提供的lock路径的结点作为全局锁，这个结点的数据类似这种格式：[_c_64e0811f-9475-44ca-aa36-c1db65ae5350-lock-0000000005]，每次获得锁时会生成这种串，释放锁时清空数据。

import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.locks.InterProcessMutex;import org.apache.curator.retry.RetryNTimes;import java.util.concurrent.TimeUnit;/** * Curator framework's distributed lock test. */public class CuratorDistrLockTest {    /** Zookeeper info */    private static final String ZK_ADDRESS = "192.168.1.100:2181";    private static final String ZK_LOCK_PATH = "/zktest";    public static void main(String[] args) throws InterruptedException {        // 1.Connect to zk        CuratorFramework client = CuratorFrameworkFactory.newClient(                ZK_ADDRESS,                new RetryNTimes(10, 5000)        );        client.start();        System.out.println("zk client start successfully!");        Thread t1 = new Thread(() -> {            doWithLock(client);        }, "t1");        Thread t2 = new Thread(() -> {            doWithLock(client);        }, "t2");        t1.start();        t2.start();    }    private static void doWithLock(CuratorFramework client) {        InterProcessMutex lock = new InterProcessMutex(client, ZK_LOCK_PATH);        try {            if (lock.acquire(10 * 1000, TimeUnit.SECONDS)) {                System.out.println(Thread.currentThread().getName() + " hold lock");                Thread.sleep(5000L);                System.out.println(Thread.currentThread().getName() + " release lock");            }        } catch (Exception e) {            e.printStackTrace();        } finally {            try {                lock.release();            } catch (Exception e) {                e.printStackTrace();            }        }    }}

1.2 Leader选举


当集群里的某个服务down机时，我们可能要从slave结点里选出一个作为新的master，这时就需要一套能在分布式环境中自动协调的Leader选举方法。Curator提供了LeaderSelector监听器实现Leader选举功能。同一时刻，只有一个Listener会进入takeLeadership()方法，说明它是当前的Leader。注意：当Listener从takeLeadership()退出时就说明它放弃了“Leader身份”，这时Curator会利用Zookeeper再从剩余的Listener中选出一个新的Leader。autoRequeue()方法使放弃Leadership的Listener有机会重新获得Leadership，如果不设置的话放弃了的Listener是不会再变成Leader的。

import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.leader.LeaderSelector;import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;import org.apache.curator.framework.state.ConnectionState;import org.apache.curator.retry.RetryNTimes;import org.apache.curator.utils.EnsurePath;/** * Curator framework's leader election test. * Output: *  LeaderSelector-2 take leadership! *  LeaderSelector-2 relinquish leadership! *  LeaderSelector-1 take leadership! *  LeaderSelector-1 relinquish leadership! *  LeaderSelector-0 take leadership! *  LeaderSelector-0 relinquish leadership!  *      ... */public class CuratorLeaderTest {    /** Zookeeper info */    private static final String ZK_ADDRESS = "192.168.1.100:2181";    private static final String ZK_PATH = "/zktest";    public static void main(String[] args) throws InterruptedException {        LeaderSelectorListener listener = new LeaderSelectorListener() {            @Override            public void takeLeadership(CuratorFramework client) throws Exception {                System.out.println(Thread.currentThread().getName() + " take leadership!");                // takeLeadership() method should only return when leadership is being relinquished.                Thread.sleep(5000L);                System.out.println(Thread.currentThread().getName() + " relinquish leadership!");            }            @Override            public void stateChanged(CuratorFramework client, ConnectionState state) {            }        };        new Thread(() -> {            registerListener(listener);        }).start();        new Thread(() -> {            registerListener(listener);        }).start();        new Thread(() -> {            registerListener(listener);        }).start();        Thread.sleep(Integer.MAX_VALUE);    }    private static void registerListener(LeaderSelectorListener listener) {        // 1.Connect to zk        CuratorFramework client = CuratorFrameworkFactory.newClient(                ZK_ADDRESS,                new RetryNTimes(10, 5000)        );        client.start();        // 2.Ensure path        try {            new EnsurePath(ZK_PATH).ensure(client.getZookeeperClient());        } catch (Exception e) {            e.printStackTrace();        }        // 3.Register listener        LeaderSelector selector = new LeaderSelector(client, ZK_PATH, listener);        selector.autoRequeue();        selector.start();    }}