架构师训练营第五周 - 作业

import java.util.LinkedList;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
import org.apache.commons.lang.StringUtils;
public class test {
    private static String[] servers = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J"};  
    private static List<String> realNodes = new LinkedList<String>();  
    private static SortedMap<Integer, String> virtualNodes = new TreeMap<Integer, String>();  
    private static final int VIRTUAL_NODES = 200;  
    static{  
        for(int i=0; i<servers.length; i++)  
            realNodes.add(servers[i]);  
        for (String str : realNodes){  
            for(int i=0; i<VIRTUAL_NODES; i++){  
                String virtualNodeName = str + "&&VN" + String.valueOf(i);  
                int hash = getHash(virtualNodeName);  
                System.out.println("虚拟节点[" + virtualNodeName + "]被添加, hash值为" + hash);  
                virtualNodes.put(hash, virtualNodeName);  
            }  
        }  
        System.out.println();  
    }  
    private static int getHash(String str){  
        final int p = 16777619;  
        int hash = (int)2166136261L;  
        for (int i = 0; i < str.length(); i++)  
            hash = (hash ^ str.charAt(i)) * p;  
        hash += hash << 13;  
        hash ^= hash >> 7;  
        hash += hash << 3;  
        hash ^= hash >> 17;  
        hash += hash << 5;  
        if (hash < 0)  
            hash = Math.abs(hash);  
        return hash;  
    }  
    private static String getServer(String key){  
        int hash = getHash(key);  
        SortedMap<Integer, String> subMap = virtualNodes.tailMap(hash);  
        String virtualNode;  
        if(subMap.isEmpty()){  
           Integer i = virtualNodes.firstKey();  
           virtualNode = virtualNodes.get(i);  
        }else{  
           Integer i = subMap.firstKey();  
           virtualNode = subMap.get(i);  
        }  
        if(StringUtils.isNotBlank(virtualNode)){  
            return virtualNode.substring(0, virtualNode.indexOf("&&"));  
        }  
        return null;  
    }  
    
    public static double Variance(List<Integer> x) {
        int m = x.size();
        double sum = 0;
        for (int i = 0; i < m; i++) {
            sum += x.get(i);
        }
        double dAve = sum / m;
        double dVar = 0;
        for (int i = 0; i < m; i++) {
            dVar += (x.get(i) - dAve) * (x.get(i) - dAve);
        }
        return dVar / m;
    }
    public static void main(String[] args){  
    	Map<String, Integer> countMap = new HashMap<>();
    	for (int i = 0; i < servers.length; i++) {
            realNodes.add(servers[i]);
            countMap.put(servers[i], 0);
        }
        for(int i=0; i<1000000; i++) {
            System.out.println("[" + "测试"+i + "]的hash值为" +  
                    getHash("测试"+i) + ", 被路由到结点[" + getServer("测试"+i) + "]");  
            countMap.put(getServer("测试"+i), countMap.get(getServer("测试"+i)) + 1);
            
        }
        System.out.println(countMap);
        
        List<Integer> x = new ArrayList<>();
        for (String key : countMap.keySet()) {
            x.add(countMap.get(key));
        }
		System.out.println("标准差=：" + Math.sqrt(Variance(x)));
    } 
}