Dubbo-负载均衡原理解析(1)，一个本科渣渣是怎么逆袭从咸鱼到Offer收割机的

System.out.println(getServer());
}
}
}

public class WeightRandomV2 {
public static String getServer() {
int totalWeight = 0;
boolean sameWeight = true; //如果所有权重都相等，随机一个ip即可
Object[] weights = ServerIps.WEIGHT_LIST.values().toArray();
for (int i = 0; i < weights.length; i++) {
Integer weight = (Integer) weights[i];
totalWeight += weight;
//判断权重是否都相等
if (sameWeight && i > 0 && !weight.equals(weights[i - 1])) {
sameWeight = false;
}
}
Random random = new Random();
int randomPos = random.nextInt(totalWeight);
//权重值不相等
if (!sameWeight) {
for (String ip : ServerIps.WEIGHT_LIST.keySet()) {
Integer value = ServerIps.WEIGHT_LIST.get(ip);
if (randomPos < value) {
return ip;
}
randomPos = randomPos - value;
}
}
return (String) ServerIps.WEIGHT_LIST.keySet().toArray()[new Random().nextInt(ServerIps.WEIGHT_LIST.size())];
}
public static void main(String[] args) {
//连续调用10次
for (int i = 0; i < 10; i++) {
System.out.println(getServer());
}
}
}

public class RoundRobin {
private static Integer pos = 0;
public static String getServer() {
String ip = “”;
//pos同步
synchronized (pos) {
if (pos >= ServerIps.LIST.size()) {
pos = 0;
}
ip = ServerIps.LIST.get(pos);
pos++;
}
return ip;
}
public static void main(String[] args) {
//连续调用10次
for (int i = 0; i < 11; i++) {
System.out.println(getServer());
}
}
}

public class Sequence {
public static Integer num=0;
public static Integer getAndIncrement(){
return ++num;
}
}
public class WeightRoundRobin {
private static Integer pos = 0;
public static String getServer() {
int totalWeight = 0;
boolean sameWeight = true;
Object[] weights = ServerIps.WEIGHT_LIST.values().toArray();
for (int i = 0; i < weights.length; i++) {
Integer weight = (Integer) weights[i];
totalWeight += weight;
if (sameWeight && i > 0 && !weight.equals(weights[i - 1])) {
sameWeight = false;
}
}
Integer sequenceNum = Sequence.getAndIncrement();
Integer offset = sequenceNum % totalWeight;
offset = offset == 0 ? totalWeight : offset;
if (!sameWeight) {
for (String ip : ServerIps.WEIGHT_LIST.keySet()) {
Integer weight = ServerIps.WEIGHT_LIST.get(ip);
if (offset <= weight) {
return ip;
}
offset = offset - weight;
}
}
String ip = “”;
synchronized (pos) {
if (pos >= ServerIps.LIST.size()) {
pos = 0;
}
ip = ServerIps.LIST.get(pos);
pos++;
}
return ip;
}
public static void main(String[] args) {
// 连续调用11次
for (int i = 0; i < 11; i++) {
System.out.println(getServer());
}
}
}

| 请求编号 | currentWeight 数组 (current_weight += weight) | 选择结果(max(currentWeight)) | 减去权重总和后的currentWeight 数组（max(currentWeight) -= sum(weight)) |
| — | — | — | — |
| 1 | [5, 1, 1] | A | [-2, 1, 1] |
| 2 | [3, 2, 2] | A | [-4, 2, 2] |
| 3 | [1, 3, 3] | B | [1, -4, 3] |
| 4 | [6, -3, 4] | A | [-1, -3, 4] |
| 5 | [4, -2, 5] | C | [4, -2, -2] |
| 6 | [9, -1, -1] | A | [2, -1, -1] |
| 7 | [7, 0, 0] | A | [0, 0, 0] |

// 增加一个Weight类，用来保存ip, weight（固定不变的原始权重）, currentweight（当前会变化的权重）
public class Weight {
private String ip;
private Integer weight;
private Integer currentWeight;
public Weight(String ip, Integer weight, Integer currentWeight) {
this.ip = ip;
this.weight = weight;
this.currentWeight = currentWeight;
}
public String getIp() {
return ip;
}
public void setIp(String ip) {
this.ip = ip;
}
public Integer getWeight() {
return weight;
}
public void setWeight(Integer weight) {
this.weight = weight;
}
public Integer getCurrentWeight() {
return currentWeight;
}
public void setCurrentWeight(Integer currentWeight) {
this.currentWeight = currentWeight;
}
}
public class WeightRoundRobinV2 {
private static Map weightMap = new HashMap();
public static String getServer() {
// 获取权重之和
int totalWeight = ServerIps.WEIGHT_LIST1.values().stream().reduce(0, (w1, w2) -> w1 + w2);
//初始化weightMap，初始时将currentWeight赋值为weight
if (weightMap.isEmpty()) {
ServerIps.WEIGHT_LIST1.forEach((key, value) -> {
weightMap.put(key, new Weight(key, value, value));
});
}
//找出currentWeight最大值
Weight maxCurrentWeight = null;
for (Weight weight : weightMap.values()) {
if (maxCurrentWeight == null || weight.getCurrentWeight() > maxCurrentWeight.getCurrentWeight()) {
maxCurrentWeight = weight;
}
}
//将maxCurrentWeight减去总权重和
maxCurrentWeight.setCurrentWeight(maxCurrentWeight.getCurrentWeight() - totalWeight);
//所有的ip的currentWeight统一加上原始权重
for (Weight weight : weightMap.values()) {
weight.setCurrentWeight(weight.getCurrentWeight() + weight.getWeight());
}
//返回maxCurrentWeight所对应的ip
return maxCurrentWeight.getIp();
}
public static void main(String[] args) {
// 连续调用10次
for (int i = 0; i < 10; i++) {
System.out.println(getServer());
}
}
}

public static final Map WEIGHT_LIST1 = new HashMap();
static {
// 权重之和为50
WEIGHT_LIST1.put(“A”, 5);
WEIGHT_LIST1.put(“B”, 1);
WEIGHT_LIST1.put(“C”, 1);
}