com.github.paganini2008.devtools.beans.streaming.Functions Maven / Gradle / Ivy

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package com.github.paganini2008.devtools.beans.streaming;

import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.List;

import com.github.paganini2008.devtools.Comparables;
import com.github.paganini2008.devtools.beans.BeanUtils;

/**
 * 
 * Functions
 * 
 * @author Fred Feng
 * 
 * @version 1.0
 */
public abstract class Functions {

	public static > Calculation min(String attributeName, Class requiredType) {
		return new Min(attributeName, requiredType);
	}

	public static > Calculation max(String attributeName, Class requiredType) {
		return new Max(attributeName, requiredType);
	}

	public static  Calculation sum(String attributeName) {
		return new Sum(attributeName);
	}

	public static  Calculation avg(String attributeName, int scale, RoundingMode roundingMode) {
		return new Avg(attributeName, scale, roundingMode);
	}

	public static class Min> implements Calculation {

		private final String attributeName;
		private final Class requiredType;

		Min(String attributeName, Class requiredType) {
			this.attributeName = attributeName;
			this.requiredType = requiredType;
		}

		public T getResult(List elements) {
			T identity = BeanUtils.getProperty(elements.get(0), attributeName, requiredType);
			return elements.stream().map(e -> {
				return BeanUtils.getProperty(e, attributeName, requiredType);
			}).reduce(identity, (left, right) -> {
				return Comparables.min(left, right);
			});
		}
	}

	public static class Max> implements Calculation {

		private final String attributeName;
		private final Class requiredType;

		Max(String attributeName, Class requiredType) {
			this.attributeName = attributeName;
			this.requiredType = requiredType;
		}

		public T getResult(List elements) {
			return elements.stream().map(e -> {
				return BeanUtils.getProperty(e, attributeName, requiredType);
			}).reduce(null, (left, right) -> {
				return Comparables.max(left, right);
			});
		}
	}

	public static class Sum implements Calculation {

		private final String attributeName;

		Sum(String attributeName) {
			this.attributeName = attributeName;
		}

		public BigDecimal getResult(List elements) {
			return elements.stream().map(e -> {
				return BeanUtils.getProperty(e, attributeName, BigDecimal.class);
			}).reduce(BigDecimal.ZERO, (left, right) -> {
				return left.add(right);
			});
		}
	}

	public static class Avg implements Calculation {

		private final String attributeName;
		private final int scale;
		private final RoundingMode roundingMode;

		Avg(String attributeName, int scale, RoundingMode roundingMode) {
			this.attributeName = attributeName;
			this.scale = scale;
			this.roundingMode = roundingMode;
		}

		public BigDecimal getResult(List elements) {
			return elements.stream().map(e -> {
				return BeanUtils.getProperty(e, attributeName, BigDecimal.class);
			}).reduce(BigDecimal.ZERO, (left, right) -> {
				return left.add(right);
			}).divide(BigDecimal.valueOf(elements.size()), scale, roundingMode);
		}
	}

}