Week5 作业一

import com.google.common.collect.Maps;
import com.google.common.hash.Hashing;
import org.javers.common.collections.Lists;
import java.io.Serializable;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;
public class ConsistentHashMap implements Serializable {
    private final int virtualNodes;
    private final List<String> servers;
    private SortedMap<Integer, String> consistentCircle;
    private Map<String, Integer> counter;
    public ConsistentHashMap(List<String> servers) {
        this.servers = new CopyOnWriteArrayList<>(servers);
        this.virtualNodes = 65535 / servers.size();
        counter = Maps.newHashMap();
        init();
    }
    public static void main(String[] args) {
        ConsistentHashMap consistentHashMap = new ConsistentHashMap(
                Lists.asList("127.0.0.1:8080", "127.0.0.1:8081", "127.0.0.1:8082", "127.0.0.1:8083", "127.0.0.1:8084", "127.0.0.1:8085", "127.0.0.1:8086", "127.0.0.1:8087", "127.0.0.1:8088", "127.0.0.1:8089"));
        for (int i = 0; i < 1000000; i++) {
            consistentHashMap.getServer(UUID.randomUUID().toString());
        }
        System.out.println(consistentHashMap.standard());
    }
    private int getHash(String str) {
        return Hashing.murmur3_32().hashBytes(str.getBytes()).asInt();
    }
    private void init() {
        consistentCircle = new TreeMap<>();
        for (int i = 0; i < servers.size(); i++) {
            for (int j = 0; j < virtualNodes; j++) {
                String virtualServer = j + "#" + servers.get(i);
                consistentCircle.put(getHash(virtualServer), virtualServer);
            }
        }
    }
    public String getServer(String key) {
        int hash = getHash(key);
        SortedMap<Integer, String> map = consistentCircle.tailMap(hash);
        if (map.isEmpty()) {
            map = consistentCircle;
        }
        Integer firstKey = map.firstKey();
        String server = map.get(firstKey);
        server = server.substring(server.indexOf("#") + 1);
        counter.put(server, counter.getOrDefault(server, 0) + 1);
        return server;
    }
    public String standard() {
        double avg = counter.values().stream().mapToInt(a -> a).average().orElse(0);
        double avgStd = counter.values().stream().map(count -> Math.pow(count - avg, 2)).mapToDouble(Double::doubleValue).average().orElse(0d);
        return String.format("%.2f", Math.sqrt(avgStd));
    }
}