详解Nginx轮询算法底层实现的方法

public class SimplePolling {

  /**
   * key是ip
   */
  public static List <String> ipService = new LinkedList <>();
  static {
    ipService.add("192.168.1.1");
    ipService.add("192.168.1.2");
    ipService.add("192.168.1.3");
  }
  public static int pos = 0;
  public static String getIp(){
    if(pos >= ipService.size()){
      //防止索引越界
      pos = 0;
    }
    String ip = ipService.get(pos);
    pos ++;
    return ip;

  }

  public static void main(String[] args) {
    for (int i = 0; i < 4; i++) {
      System.out.println(getIp());

    }
  }
}

public class WeightPolling {

  /**
   * key是ip,value是权重
   */
  public static Map<String, Integer> ipService = new LinkedHashMap<>();
  static {
    ipService.put("192.168.1.1", 5);
    ipService.put("192.168.1.2", 1);
    ipService.put("192.168.1.3", 1);
  }
  public static int requestId = 0;
  public static int getAndIncrement() {
    return requestId++;
  }

  public static String getIp(){
    //获取总的权重
    int totalWeight =0;
    for (Integer value : ipService.values()) {
      totalWeight+= value;
    }
    //获取当前轮询的值
    int andIncrement = getAndIncrement();
    int pos = andIncrement% totalWeight;
    for (String ip : ipService.keySet()) {
      if(pos < ipService.get(ip)){
        return ip;
      }
      pos -= ipService.get(ip);
    }
    return null;
  }

  public static void main(String[] args) {
    for (int i = 0; i < 7; i++) {
      System.out.println(getIp());
    }
  }

}

public class Polling {

  /**
   * key是ip,value是权重
   */
  public static Map <String,Integer> ipService = new LinkedHashMap <>();
  static {
    ipService.put("192.168.1.1",5);
    ipService.put("192.168.1.2",1);
    ipService.put("192.168.1.3",1);
  }
  private static Map<String,Weight> weightMap = new LinkedHashMap <>();

  public static String getIp(){
    //计算总的权重
     int totalWeight = 0;
    for (Integer value : ipService.values()) {
      totalWeight+=value;
    }
    //首先判断weightMap是否为空
    if(weightMap.isEmpty()){
      ipService.forEach((ip,weight)->{
        Weight weights = new Weight(ip, weight,0);
        weightMap.put(ip,weights);
      });
    }
    //给map中得对象设置当前权重
    weightMap.forEach((ip,weight)->{
      weight.setCurrentWeight(weight.getWeight() + weight.getCurrentWeight());
    });

    //判断最大权重是否大于当前权重,如果为空或者小于当前权重，则把当前权重赋值给最大权重
    Weight maxWeight = null;
    for (Weight weight : weightMap.values()) {
      if(maxWeight ==null || weight.getCurrentWeight() > maxWeight.getCurrentWeight()){
        maxWeight = weight;
      }
    }
    //最后把当前最大权重减去总的权重
    maxWeight.setCurrentWeight(maxWeight.getCurrentWeight() - totalWeight);
    //返回
    return maxWeight.getIp();
  }

  public static void main(String[] args) {
    //模拟轮询7次取ip
    for (int i = 0; i < 7; i++) {
      System.out.println(getIp());
    }
  }

}

class Weight{
  /**
   * ip
   */
  private String ip;
  /**
   * 设置得权重
   */
  private int weight;
  /**
   * 当前权重
   */
  private int currentWeight;

  public Weight(String ip, int weight,int currentWeight) {
    this.ip = ip;
    this.weight = weight;
    this.currentWeight = currentWeight;
  }

  public String getIp() {
    return ip;
  }

  public void setIp(String ip) {
    this.ip = ip;
  }

  public int getWeight() {
    return weight;
  }

  public void setWeight(int weight) {
    this.weight = weight;
  }

  public int getCurrentWeight() {
    return currentWeight;
  }

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