【架构师训练营】第五周作业

package com.houzh.hash;
import com.google.common.collect.Lists;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;
/**
 * @Author: houzh
 * @Date: 2020/7/8 9:59 上午
 */
public class ConsistentHashVirtualNode {
    private static String[] servers = {"192.168.0.1:8080", "192.168.0.2:8080", "192.168.0.3:8080",
            "192.168.0.4:8080", "192.168.0.5:8080", "192.168.0.6:8080", "192.168.0.7:8080", "192.168.0.8:8080", "192.168.0.9:8080", "192.168.0.10:8080"};
    private static LinkedList<String> realNodes = Lists.newLinkedList();
    private static SortedMap<Long, String> virtualNodes = new TreeMap<>();
    public static final int VIRTUAL_NODE = 200;
    public static String[] keys = new String[1000000];
    static {
        for (int i = 0; i < 1000000; i++) {
            keys[i] = String.valueOf(i);
        }
        for (int i = 0; i < servers.length; i++) {
            realNodes.add(servers[i]);
        }
        for (String realNode : realNodes) {
            for (int i = 0; i < VIRTUAL_NODE; i++) {
                String virtualNodeName = realNode + "&NO=" + i;
                long hash = getHash(virtualNodeName);
                virtualNodes.put(hash, virtualNodeName);
            }
        }
    }
    private static String getServer(String key) {
        long hash = getHash(key);
        SortedMap<Long, String> subMap = virtualNodes.tailMap(hash);
        String virtualNode;
        if (subMap.isEmpty()) {
            Long aLong = virtualNodes.firstKey();
            virtualNode = virtualNodes.get(aLong);
        } else {
            Long aLong = subMap.firstKey();
            virtualNode = subMap.get(aLong);
        }
        return virtualNode.substring(0, virtualNode.indexOf("&"));
    }
    private static long getHash(String value) {
        byte[] bytes = md5(value);
        return hash(bytes, 0);
    }
    private static long hash(byte[] digest, int number) {
        return (((long) (digest[3 + number * 4] & 0xFF) << 24)
                | ((long) (digest[2 + number * 4] & 0xFF) << 16)
                | ((long) (digest[1 + number * 4] & 0xFF) << 8)
                | (digest[0 + number * 4] & 0xFF))
                & 0xFFFFFFFFL;
    }
    private static byte[] md5(String value) {
        MessageDigest md5;
        try {
            md5 = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        md5.reset();
        byte[] bytes;
        try {
            bytes = value.getBytes("UTF-8");
        } catch (UnsupportedEncodingException e) {
            throw new IllegalStateException(e.getMessage(), e);
        }
        md5.update(bytes);
        return md5.digest();
    }
    public static void main(String[] args) {
        SortedMap<String, AtomicInteger> map = new TreeMap<>();
        for (int i = 0; i < keys.length; i++) {
            String server = getServer(keys[i]);
            map.putIfAbsent(server, new AtomicInteger(0));
            map.get(server).incrementAndGet();
        }
        Iterator<Map.Entry<String, AtomicInteger>> entries = map.entrySet().iterator();
        while (entries.hasNext()) {
            Map.Entry<String, AtomicInteger> entry = entries.next();
            System.out.println(entry.getKey() + ":" + entry.getValue());
        }
    }
}