java8listBigDecimal求和
⾃定义⼀个新的list对BigDecimal求和的⼯具类，封装求和，最⼤值，最⼩值，平均值
下⾯有贴代码出来
//测试数据类
@Data
@Accessors(chain =true)//开启链式编程
static class Test{
Long id;
Integer type;
BigDecimal money;
}
使⽤⾃定义的CollectorsUtil类进⾏list求和
ArrayList<Test> list = wArrayList(
new Test().setId(1L).setType(1).setMoney(BigDecimal.ONE),
new Test().setId(1L).setType(2).setMoney(BigDecimal.TEN),
new Test().setId(1L).setType(1).setMoney(BigDecimal.ZERO),
new Test().setId(1L).setType(2).setMoney(BigDecimal.ONE),
new Test().setId(1L).setType(3).setMoney(BigDecimal.valueOf(5))
);
BigDecimal collect = list.stream().collect(CollectorsUtil.summingBigDecimal(Test::getMoney));
System.out.println("collect = "+ collect);
//运⾏结果 collect = 17
使⽤⾃定义的CollectorsUtil类进⾏list分组求和
Map<Integer, BigDecimal> collect1 = list.stream().upingBy(Test::getType, CollectorsUtil.summingBigDecimal(Test::getMoney))); System.out.println("collect1 = "+ collect1);
//运⾏结果 collect = {1=1, 2=11, 3=5}
import com.nanase.takeshi.annotion.ToBigDecimalFunction;
import java.math.BigDecimal;
import java.math.MathContext;
import java.util.Collections;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
/**
* JAVA8 分组求和要⽤到的
* 使⽤⽅法
* list.stream().upingBy(Entry::getName, CollectorsUtil.summingBigDecimal(Entry::getValue)));
* list.stream().collect(CollectorsUtil.summingBigDecimal(Entry::getValue));
* CollectorsUtil
*
* @author 725
* @date 2020/12/31 16:25
*/
public class CollectorsUtil {
private static final Set<Collector.Characteristics> CHARACTERISTICS = ptySet();
private CollectorsUtil(){
}
@SuppressWarnings("unchecked")
private static<I, R> Function<I, R>castingIdentity(){
return i ->(R) i;
}
}
/**
* Simple implementation class for {@code Collector}.
*
* @param <T> the type of elements to be collected
* @param <R> the type of the result
*/
@SuppressWarnings("hiding")
static class CollectorImpl<T, A, R>implements Collector<T, A, R>{
private final Supplier<A> supplier;
private final BiConsumer<A, T> accumulator;
private final BinaryOperator<A> combiner;
private final Function<A, R> finisher;
private final Set<Characteristics> characteristics;
CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Function<A, R> finisher,
Set<Characteristics> characteristics){
this.supplier = supplier;
this.accumulator = accumulator;
thisbiner = combiner;
this.finisher = finisher;
this.characteristics = characteristics;
}
CollectorImpl(Supplier<A> supplier,
BiConsumer<A, T> accumulator,
BinaryOperator<A> combiner,
Set<Characteristics> characteristics){
this(supplier, accumulator, combiner,castingIdentity(), characteristics);
}
@Override
public BiConsumer<A, T>accumulator(){
return accumulator;
}
@Override
public Supplier<A>supplier(){
return supplier;
}
@Override
public BinaryOperator<A>combiner(){
return combiner;
}
@Override
public Function<A, R>finisher(){
return finisher;
}
@Override
public Set<Characteristics>characteristics(){
return characteristics;
}
}
/**
* 求和⽅法
*
* @param mapper
* @param <T>
* @return
*/
*/
public static<T> Collector<T,?, BigDecimal>summingBigDecimal(ToBigDecimalFunction<?super T> mapper){
return new CollectorImpl<>(
()->new BigDecimal[]{new BigDecimal(0)},
(a, t)->{
a[0]= a[0].add(mapper.applyAsBigDecimal(t), MathContext.DECIMAL32);
},
(a, b)->{
a[0]= a[0].add(b[0], MathContext.DECIMAL32);
return a;
},
a -> a[0], CHARACTERISTICS);
}
/**
* 求最⼤，这⾥的最⼩MIN值，作为初始条件判断值，如果某些数据范围超过百亿以后，可以根据需求换成Long.MIN_VALUE或者Double.MIN_VALUE
*
* @param mapper
* @param <T>
* @return
*/
public static<T> Collector<T,?, BigDecimal>maxBy(ToBigDecimalFunction<?super T> mapper){
return new CollectorImpl<>(
()->new BigDecimal[]{new BigDecimal(Integer.MIN_VALUE)},
(a, t)->{
a[0]= a[0].max(mapper.applyAsBigDecimal(t));
},java stream
(a, b)->{
a[0]= a[0].max(b[0]);
return a;
},
a -> a[0], CHARACTERISTICS);
}
/**
* 求最⼩，这⾥的最⼤MAX值，作为初始条件判断值，如果某些数据范围超过百亿以后，可以根据需求换成Long.MAX_VALUE或者Double.MAX_VALUE      *
* @param mapper
* @param <T>
* @return
*/
public static<T> Collector<T,?, BigDecimal>minBy(ToBigDecimalFunction<?super T> mapper){
return new CollectorImpl<>(
()->new BigDecimal[]{new BigDecimal(Integer.MAX_VALUE)},
(a, t)->{
a[0]= a[0].min(mapper.applyAsBigDecimal(t));
},
(a, b)->{
a[0]= a[0].min(b[0]);
return a;
},
a -> a[0], CHARACTERISTICS);
}
/**
* 求平均，并且保留⼩数，返回⼀个平均值
*
* @param newScale    保留⼩数位数
* @param roundingMode ⼩数处理⽅式
*                    #ROUND_UP 进1
*                    #ROUND_DOWN 退1
*                    #ROUND_CEILING  进1截取：正数则ROUND_UP，负数则ROUND_DOWN
*                    #ROUND_FLOOR  退1截取：正数则ROUND_DOWN，负数则ROUND_UP
*                    #ROUND_HALF_UP >=0.5进1
*                    #ROUND_HALF_DOWN >0.5进1
*                    #ROUND_HALF_EVEN
*                    #ROUND_UNNECESSARY
*/
public static<T> Collector<T,?, BigDecimal>averagingBigDecimal(ToBigDecimalFunction<?super T> mapper,int newScale,int roundingMode){ return new CollectorImpl<>(
return new CollectorImpl<>(
()->new BigDecimal[]{new BigDecimal(0),new BigDecimal(0)},
(a, t)->{
a[0]= a[0].add(mapper.applyAsBigDecimal(t));
a[1]= a[1].add(BigDecimal.ONE);
},
(a, b)->{
a[0]= a[0].add(b[0]);
return a;
},
a -> a[0].divide(a[1], MathContext.DECIMAL32).setScale(newScale, roundingMode), CHARACTERISTICS); }
}