cn.hutool.core.lang.WeightRandom Maven / Gradle / Ivy
package cn.hutool.core.lang;
import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.map.MapUtil;
import cn.hutool.core.util.RandomUtil;
import java.io.Serializable;
import java.util.Random;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* 权重随机算法实现
*
* 平时，经常会遇到权重随机算法，从不同权重的N个元素中随机选择一个，并使得总体选择结果是按照权重分布的。如广告投放、负载均衡等。
*
*
* 如有4个元素A、B、C、D，权重分别为1、2、3、4，随机结果中A:B:C:D的比例要为1:2:3:4。
*
* 总体思路：累加每个元素的权重A(1)-B(3)-C(6)-D(10)，则4个元素的的权重管辖区间分别为[0,1)、[1,3)、[3,6)、[6,10)。
* 然后随机出一个[0,10)之间的随机数。落在哪个区间，则该区间之后的元素即为按权重命中的元素。
*
*
* 参考博客：https://www.cnblogs.com/waterystone/p/5708063.html
*
*
* @param 权重随机获取的对象类型
* @author looly
* @since 3.3.0
*/
public class WeightRandom implements Serializable {
private static final long serialVersionUID = -8244697995702786499L;
private final TreeMap weightMap;
/**
* 创建权重随机获取器
*
* @param 权重随机获取的对象类型
* @return {@link WeightRandom}
*/
public static WeightRandom create() {
return new WeightRandom<>();
}
// ---------------------------------------------------------------------------------- Constructor start
/**
* 构造
*/
public WeightRandom() {
weightMap = new TreeMap<>();
}
/**
* 构造
*
* @param weightObj 带有权重的对象
*/
public WeightRandom(WeightObj weightObj) {
this();
if(null != weightObj) {
add(weightObj);
}
}
/**
* 构造
*
* @param weightObjs 带有权重的对象
*/
public WeightRandom(Iterable> weightObjs) {
this();
if(CollUtil.isNotEmpty(weightObjs)) {
for (WeightObj weightObj : weightObjs) {
add(weightObj);
}
}
}
/**
* 构造
*
* @param weightObjs 带有权重的对象
*/
public WeightRandom(WeightObj[] weightObjs) {
this();
for (WeightObj weightObj : weightObjs) {
add(weightObj);
}
}
// ---------------------------------------------------------------------------------- Constructor end
/**
* 增加对象
*
* @param obj 对象
* @param weight 权重
* @return this
*/
public WeightRandom add(T obj, double weight) {
return add(new WeightObj<>(obj, weight));
}
/**
* 增加对象权重
*
* @param weightObj 权重对象
* @return this
*/
public WeightRandom add(WeightObj weightObj) {
if(null != weightObj) {
final double weight = weightObj.getWeight();
if(weightObj.getWeight() > 0) {
double lastWeight = (this.weightMap.size() == 0) ? 0 : this.weightMap.lastKey();
this.weightMap.put(weight + lastWeight, weightObj.getObj());// 权重累加
}
}
return this;
}
/**
* 清空权重表
*
* @return this
*/
public WeightRandom clear() {
if(null != this.weightMap) {
this.weightMap.clear();
}
return this;
}
/**
* 下一个随机对象
*
* @return 随机对象
*/
public T next() {
if(MapUtil.isEmpty(this.weightMap)) {
return null;
}
final Random random = RandomUtil.getRandom();
final double randomWeight = this.weightMap.lastKey() * random.nextDouble();
final SortedMap tailMap = this.weightMap.tailMap(randomWeight, false);
return this.weightMap.get(tailMap.firstKey());
}
/**
* 带有权重的对象包装
*
* @author looly
*
* @param 对象类型
*/
public static class WeightObj {
/** 对象 */
private T obj;
/** 权重 */
private final double weight;
/**
* 构造
*
* @param obj 对象
* @param weight 权重
*/
public WeightObj(T obj, double weight) {
this.obj = obj;
this.weight = weight;
}
/**
* 获取对象
*
* @return 对象
*/
public T getObj() {
return obj;
}
/**
* 设置对象
*
* @param obj 对象
*/
public void setObj(T obj) {
this.obj = obj;
}
/**
* 获取权重
*
* @return 权重
*/
public double getWeight() {
return weight;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((obj == null) ? 0 : obj.hashCode());
long temp;
temp = Double.doubleToLongBits(weight);
result = prime * result + (int) (temp ^ (temp >>> 32));
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
WeightObj other = (WeightObj) obj;
if (this.obj == null) {
if (other.obj != null) {
return false;
}
} else if (!this.obj.equals(other.obj)) {
return false;
}
return Double.doubleToLongBits(weight) == Double.doubleToLongBits(other.weight);
}
}
}