Detailed explanation of the underlying implementation method of Nginx polling algorithm

public class SimplePolling {

  /**
   * key is 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()){
      //Prevent index from going out of bounds 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 is ip, value is weight*/
  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(){
    //Get the total weight int totalWeight =0;
    for (Integer value : ipService.values()) {
      totalWeight+= value;
    }
    //Get the current polling value 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 is ip, value is weight*/
  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(){
    //Calculate the total weight int totalWeight = 0;
    for (Integer value : ipService.values()) {
      totalWeight+=value;
    }
    //First determine whether weightMap is empty if (weightMap.isEmpty()) {
      ipService.forEach((ip,weight)->{
        Weight weights = new Weight(ip, weight,0);
        weightMap.put(ip,weights);
      });
    }
    //Set the current weight for the object in the map weightMap.forEach((ip,weight)->{
      weight.setCurrentWeight(weight.getWeight() + weight.getCurrentWeight());
    });

    //Judge whether the maximum weight is greater than the current weight. If it is empty or less than the current weight, assign the current weight to the maximum weight. Weight maxWeight = null;
    for (Weight weight : weightMap.values()) {
      if(maxWeight == null || weight.getCurrentWeight() > maxWeight.getCurrentWeight()){
        maxWeight = weight;
      }
    }
    //Finally, subtract the total weight from the current maximum weight maxWeight.setCurrentWeight(maxWeight.getCurrentWeight() - totalWeight);
    //return return maxWeight.getIp();
  }

  public static void main(String[] args) {
    //Simulate polling 7 times to get IP
    for (int i = 0; i < 7; i++) {
      System.out.println(getIp());
    }
  }

}

class Weight{
  /**
   * ip
   */
  private String ip;
  /**
   * Set the weight */
  private int weight;
  /**
   * Current weight */
  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;
  }
}