一致性哈希 java代码实例

以下是一致性哈希的 Java 代码实现，以字符串的哈希值作为节点的标识：

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;

public class ConsistentHash {

    private final MessageDigest md5;
    private final int numberOfReplicas;
    private final SortedMap<Long, String> circle = new TreeMap<>();

    public ConsistentHash(int numberOfReplicas) {
        try {
            this.md5 = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException("MD5 algorithm not available");
        }
        this.numberOfReplicas = numberOfReplicas;
    }

    public void addNode(String node) {
        for (int i = 0; i < numberOfReplicas; i++) {
            String replicaKey = getReplicaKey(node, i);
            long hash = hashKey(replicaKey);
            circle.put(hash, node);
        }
    }

    public void removeNode(String node) {
        for (int i = 0; i < numberOfReplicas; i++) {
            String replicaKey = getReplicaKey(node, i);
            long hash = hashKey(replicaKey);
            circle.remove(hash);
        }
    }

    public String getNode(String key) {
        if (circle.isEmpty()) {
            return null;
        }
        long hash = hashKey(key);
        if (!circle.containsKey(hash)) {
            SortedMap<Long, String> tailMap = circle.tailMap(hash);
            hash = tailMap.isEmpty() ? circle.firstKey() : tailMap.firstKey();
        }
        return circle.get(hash);
    }

    private String getReplicaKey(String node, int i) {
        return node + ":" + i;
    }

    private long hashKey(String key) {
        md5.reset();
        md5.update(key.getBytes());
        byte[] digest = md5.digest();
        long h = 0;
        for (int i = 0; i < 4; i++) {
            h <<= 8;
            h |= ((int) digest[i]) & 0xFF;
        }
        return h;
    }
}

以下是一个简单的测试：

ConsistentHash consHash = new ConsistentHash(100);

consHash.addNode("node1");
consHash.addNode("node2");
consHash.addNode("node3");

System.out.println(consHash.getNode("key1"));  // 输出 node1
System.out.println(consHash.getNode("key2"));  // 输出 node2

consHash.removeNode("node2");

System.out.println(consHash.getNode("key1"));  // 输出 node1
System.out.println(consHash.getNode("key2"));  // 输出 node3

以上代码实现了一致性哈希的基本功能，包括添加节点、删除节点、根据键值获取节点等。