public class SmoothWeightedRoundRobin {
    private volatile List<Node> nodeList = new ArrayList<>() ; // 保存權(quán)重
    private ReentrantLock lock = new ReentrantLock() ;

    public SmoothWeightedRoundRobin(Node ...nodes) {
        for (Node node : nodes) {
            nodeList.add(node) ;
        }
    }

    public Node select(){
        try {
            lock.lock();
            return this.selectInner() ;
        }finally {
            lock.unlock();
        }
    }

    private Node selectInner(){
        int totalWeight = 0 ;
        Node maxNode = null ;
        int maxWeight = 0 ;

        for (int i = 0; i < nodeList.size(); i++) {
            Node n = nodeList.get(i);
            totalWeight += n.getWeight() ;

            // 每個(gè)節(jié)點(diǎn)的當(dāng)前權(quán)重要加上原始的權(quán)重
            n.setCurrentWeight(n.getCurrentWeight() + n.getWeight());

            // 保存當(dāng)前權(quán)重最大的節(jié)點(diǎn)
            if (maxNode == null || maxWeight < n.getCurrentWeight() ) {
                maxNode = n ;
                maxWeight = n.getCurrentWeight() ;
            }
        }
        // 被選中的節(jié)點(diǎn)權(quán)重減掉總權(quán)重
        maxNode.setCurrentWeight(maxNode.getCurrentWeight() - totalWeight);

//        nodeList.forEach(node -> System.out.print(node.getCurrentWeight()));
        return maxNode ;
    }
}

public class Node {
    private final int weight ;  // 初始權(quán)重 （保持不變）
    private final String serverName ; // 服務(wù)名

    private int currentWeight ; // 當(dāng)前權(quán)重

    public Node( String serverName, int weight) {
        this.weight = weight;
        this.serverName = serverName ;
        this.currentWeight = weight ;
    }

    public int getCurrentWeight() {
        return currentWeight;
    }

    public int getWeight() {
        return weight;
    }

    public void setCurrentWeight(int currentWeight) {
        this.currentWeight = currentWeight;
    }

    public String getServerName() {
        return serverName;
    }
}

public class Test {

    public static void main(String[] args) {
        /**
         * 假設(shè)有三個(gè)服務(wù)器權(quán)重配置如下：
         * server A  weight = 4 ;
         * server B  weight = 3 ;
         * server C  weight = 2 ;
         */
        Node serverA = new Node("serverA", 4);
        Node serverB = new Node("serverB", 3);
        Node serverC = new Node("serverC", 2);

        SmoothWeightedRoundRobin smoothWeightedRoundRobin = new SmoothWeightedRoundRobin(serverA, serverB, serverC);
        for (int i = 0; i < 7; i++) {
            Node i1 = smoothWeightedRoundRobin.select();
            System.out.println(i1.getServerName());
        }
    }
/**
     * serverA
     * serverB
     * serverC
     * serverA
     * serverB
     * serverA
     * serverC
     */
}