一致性hash算法java实现

来源：互联网发布：淘宝设置全屏代码编辑：程序博客网时间：2024/04/25 12:57

思路：利用JDK中TreeMap的排序功能进行hash环的映射

实现代码如下：

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packagecom.sccoder.algorithm;
 
importjava.util.SortedMap;
importjava.util.TreeMap;
 
importorg.apache.commons.codec.digest.DigestUtils;
 
/**
 *
 * @author 亦凡 一致性hash算法的实现
 */
publicclassConsistencyHash<T> {
 
    /**
     * 存储服务器信息，key为服务器的hash值，TreeMap根据key进行了排序，便于查找映射节点
     */
    privateTreeMap<Long, T> serverNodes = null;
 
    publicConsistencyHash() {
        serverNodes = newTreeMap<>();
    }
 
    publicConsistencyHash(T[] servers) {
        serverNodes = newTreeMap<>();
        for(T server : servers) {
            addServer(server);
        }
    }
 
    /**
     * 映射服务器到hash环上
     */
    publicvoidaddServer(T server) {
        serverNodes.put(hash(server), server);
    }
 
    /**
     * 从hash环上移除服务器
     */
    publicvoidremoveServer(T server) {
        serverNodes.remove(hash(server));
    }
 
    /**
     * 根据key的hash值在hash环上的映射查找key映射的服务器
     *
     * @param keyHash
     * @return
     */
    publicT getServerNode(Long keyHash) {
        if(serverNodes == null) {
            returnnull;
        }
        SortedMap<Long, T> tailMap = serverNodes.tailMap(keyHash);
        if(tailMap.isEmpty()) {
            keyHash = serverNodes.firstKey();
        }else{
            keyHash = tailMap.firstKey();
        }
        returnserverNodes.get(keyHash);
    }
 
    /**
     * 打印server节点映射顺序
     */
    publicvoidprintServerMapOrder() {
        System.out.println(serverNodes);
    }
 
    /**
     * 计算hash
     *
     * @param obj
     * @return
     */
    publicstaticlong hash(Object obj) {
        byte[] data = DigestUtils.md5(obj.toString().getBytes());
        returndata[0] | ((long) data[1] << 8) | ((long) data[2] << 16)
                | ((long) data[3] << 24) | ((long) data[4] << 32)
                | ((long) data[5] << 40) | ((long) data[6] << 48)
                | ((long) data[7] << 56);
    }
 
    /**
     * byte数组转化为long数组
     *
     * @param byteArray
     * @return
     */
    publicstaticlong byteToLong(byte[] byteArray) {
        returnLong.parseLong(newString(byteArray));
    }
 
}

下面用数据做一下测试:

加入5条服务器信息，并将5条数据映射到服务器上，查看映射情况。

然后移除server3，查看数据映射情况变化。

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packagecom.sccoder.algorithm;
 
/**
 *
 * @author 亦凡
 *
 */
publicclassTest {
 
    publicstaticvoid main(String[] args) {
 
        String[] servers = newString[] { "Server 1:192.168.1.1",
                "Server 2:192.168.1.2","Server 3:192.168.1.3",
                "Server 4:192.168.1.4","Server 5:192.168.1.5" };
 
        ConsistencyHash<String> consHash = newConsistencyHash<>(servers);
        System.out.println("服务器映射信息：");
        consHash.printServerMapOrder();
        System.out.println("数据映射信息：");
        showDataMap(consHash);
        // 移除server2
        consHash.removeServer(servers[2]);
        System.out.println("移除server 3后数据映射信息：");
        showDataMap(consHash);
 
    }
 
    publicstaticvoid showDataMap(ConsistencyHash<String> consHash) {
        for(inti = 0; i < 5; i++) {
            System.out.println("Data"+ i + " mapped at "
                    + consHash.getServerNode(ConsistencyHash.hash("Data"+ i)));
        }
 
    }
 
}

打印结果如下：

服务器映射信息：
{-1886886=Server 4:192.168.1.4, -27899=Server 2:192.168.1.2, -81=Server 5:192.168.1.5, -46=Server 1:192.168.1.1, -19=Server 3:192.168.1.3}
数据映射信息：
Data0 mapped at Server 5:192.168.1.5
Data1 mapped at Server 5:192.168.1.5
Data2 mapped at Server 3:192.168.1.3
Data3 mapped at Server 4:192.168.1.4
Data4 mapped at Server 4:192.168.1.4
移除server 3后数据映射信息：
Data0 mapped at Server 5:192.168.1.5
Data1 mapped at Server 5:192.168.1.5
Data2 mapped at Server 4:192.168.1.4
Data3 mapped at Server 4:192.168.1.4
Data4 mapped at Server 4:192.168.1.4

server3在hash环上的顺序在server4前面，所以移除server3后，映射到server3上面的数据就会映射到server4上面。在服务器崩溃之后，只会影响这一台服务器上面数据的可用性。其他服务器是不会受影响的。

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