Zookeeper + Guava loading cache 实现分布式缓存

1. 概述

项目中，创建的活动内容存入redis，然后需要用到活动内容的地方，从redis去取，然后参与计算。

活动数据的一个特点是更新不频繁、数据量不大。因为项目部署一般是多机器、多实例，除了redis，有没有其他实现呢？

Guava的 loading cache是本地缓存，数据量不是很大时 可以适用(如果有大量的key-value数据缓存本地，本机也吃不消啊)，

然后多机器多实例怎么同步呢？想到了zookeeper....

2. 代码

2.1 模拟多实例

package TestZK;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
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.curator.retry.ExponentialBackoffRetry;

/**
 * @Author: rocky
 * @Date: Created in 2018/5/20.
 */
public class InstanceOne {
    private static final String ADDRESS = "xxx:2181";
    private static final String PATH = "/strategy";
    private static CuratorFramework client;
    static {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
        client = CuratorFrameworkFactory.builder()
                .connectString(ADDRESS)
                .sessionTimeoutMs(5000)
                .connectionTimeoutMs(5000)
                .retryPolicy(retryPolicy)
//                .namespace(BASE)
                .build();
        client.start();
    }

    public static void main(String[] args) throws Exception {
        startCache();
        Thread.sleep(Integer.MAX_VALUE);
    }

    private static void startCache() throws Exception {
        PathChildrenCache childrenCache = new PathChildrenCache(client, PATH, true);
        childrenCache.start();
        childrenCache.getListenable().addListener(new PathChildrenCacheListener() {
            public void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent event) throws Exception {
                System.out.println("catch that: the path of changed node "+ event.getData().getPath()
                        + ", the data of changed node is " + new String(event.getData().getData()));
                //load data to loading cache(guava)
                doSomething();
            }
        });
    }
    //load data to loading cache
    private static void doSomething() {
//        LoadingCache<String, Map<Integer, DriverIntegral>> driverIntegralCache = CacheBuilder.newBuilder().maximumSize(500)
//                .expireAfterWrite(5, TimeUnit.MINUTES).build(new CacheLoader<String, Map<Integer, DriverIntegral>>() {
//                    @Override
//                    public Map<Integer, DriverIntegral> load(String key) throws Exception {
//                        Map<Integer, DriverIntegral> integerDriverIntegralMap = ..;
//                        logger.info("guava load ::driverIntegralMap"+integerDriverIntegralMap!=null?integerDriverIntegralMap.toString():"");
//                        return integerDriverIntegralMap;
//                    }
//                });
//
//        Map<Integer, DriverIntegral> driverIntegralMap = driverIntegralCache.get(INTEGRAL);
    }
}

package TestZK;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
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.curator.retry.ExponentialBackoffRetry;

/**
 * @Author: rocky
 * @Date: Created in 2018/5/20.
 */
public class InstanceTwo {
    private static final String ADDRESS = "xxx:2181";
    private static final String PATH = "/strategy";
    private static CuratorFramework client;
    static {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
        client = CuratorFrameworkFactory.builder()
                .connectString(ADDRESS)
                .sessionTimeoutMs(5000)
                .connectionTimeoutMs(5000)
                .retryPolicy(retryPolicy)
//                .namespace(BASE)
                .build();
        client.start();
    }

    public static void main(String[] args) throws Exception {
        startCache();
        Thread.sleep(Integer.MAX_VALUE);
    }

    private static void startCache() throws Exception {
        PathChildrenCache childrenCache = new PathChildrenCache(client, PATH, true);
        childrenCache.start();
        childrenCache.getListenable().addListener(new PathChildrenCacheListener() {
            public void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent event) throws Exception {
                System.out.println("catch that: the path of changed node "+ event.getData().getPath()
                        + ", the data of changed node is " + new String(event.getData().getData()));
            }
        });
    }
}

package TestZK;

        import org.apache.curator.RetryPolicy;
        import org.apache.curator.framework.CuratorFramework;
        import org.apache.curator.framework.CuratorFrameworkFactory;
        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.curator.retry.ExponentialBackoffRetry;

/**
 * @Author: rocky
 * @Date: Created in 2018/5/20.
 */
public class InstanceThree {
    private static final String ADDRESS = "xxx:2181";
    private static final String PATH = "/strategy";
    private static CuratorFramework client;
    static {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
        client = CuratorFrameworkFactory.builder()
                .connectString(ADDRESS)
                .sessionTimeoutMs(5000)
                .connectionTimeoutMs(5000)
                .retryPolicy(retryPolicy)
//                .namespace(BASE)
                .build();
        client.start();
    }

    public static void main(String[] args) throws Exception {
        startCache();
        Thread.sleep(Integer.MAX_VALUE);
    }

    private static void startCache() throws Exception {
        PathChildrenCache childrenCache = new PathChildrenCache(client, PATH, true);
        childrenCache.start();
        childrenCache.getListenable().addListener(new PathChildrenCacheListener() {
            public void childEvent(CuratorFramework curatorFramework, PathChildrenCacheEvent event) throws Exception {
                System.out.println("catch that: the path of changed node is "+ event.getData().getPath()
                        + ", the data of changed node is " +  new String(event.getData().getData()));
            }
        });
    }
}

监听zk孩子节点，有变化时(创建、更新、删除)，重新从DB加载活动数据，缓存到loading cache，用到活动数据的地方，从cache中取。

2.2 模拟客户端

package TestZK;

import org.apache.curator.RetryPolicy;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.retry.ExponentialBackoffRetry;

/**
 * @Author: rocky
 * @Date: Created in 2018/5/20.
 */
public class NodeChangeTest {
    private static final String ADDRESS = "xxx:2181";
    private static final String PATH = "/strategy";
    private static CuratorFramework client;
    static {
        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);
        client = CuratorFrameworkFactory.builder()
                .connectString(ADDRESS)
                .sessionTimeoutMs(5000)
                .connectionTimeoutMs(5000)
                .retryPolicy(retryPolicy)
//                .namespace(BASE)
                .build();
        client.start();
    }

    public static void main(String[] args) throws Exception {
        String path_node_1 = PATH + "/node_1";
        //create
        client.create().creatingParentsIfNeeded().forPath(path_node_1);
        Thread.sleep(2000);
        //change
        client.setData().forPath(path_node_1, "yahahaha".getBytes());
        Thread.sleep(2000);
        //delete
        client.delete().forPath(path_node_1);
        Thread.sleep(Integer.MAX_VALUE);
    }
}

客户端实际上可能是某个后台，在后台创建、修改、或删除某活动，然后对应操作zookeeper节点，其他监听到节点变化的地方，做相应操作(如查询DB并缓存数据)

控制台

3. 说明

Zookeeper原生的API只能实现一次监听，这里用到的Curator的封装jar包，免去了手动重复注册。另外Curator的NodeCache和TreeCache分别监听本节点及分支所有节点，

该实例演示的PathChildrenCache只能监控一级子节点(即儿子节点、孙子节点也不能监控)，根据需要选择相应NodeCache.

很low的实现，请多指教^_^

Zookeeper Curator API 使用 www.cnblogs.com/rocky-fang/p/9037509.html

Zookeeper JAVA API的使用 http://www.cnblogs.com/rocky-fang/p/9030438.html