Java 8 stream 分组 合并

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使用很简单，功能很强大

package com.lee;import java.util.ArrayList;import java.util.List;import java.util.Optional;import java.util.stream.Collectors;public class Main {    public static void main(String[] args) {        List<Buss> bussList = new ArrayList<>();        bussList.add(new Buss("a",10,0.3));        bussList.add(new Buss("b",3,0.8));        bussList.add(new Buss("c",5,2.0));        bussList.add(new Buss("b",30,3.2));        bussList.add(new Buss("c",20,0.1));        List<Buss> st = new ArrayList<>();        bussList.stream()                .collect(Collectors.groupingBy(Buss::getName)) //分组(Name can't be null)                .forEach((k,v) -> {                    Optional<Buss> sum = v.stream().reduce((v1,v2) -> {  //合并                        v1.setCount(v1.getCount()+v2.getCount());                        v1.setValue(v1.getValue()+v2.getValue());                        return v1;                    });                    st.add(sum.orElse(new Buss("other",0,0.0)));                });        System.out.println(st);    }}class Buss {    private String name;    private int count;    private double value;    public Buss(String name, int count, double value) {        this.name = name;        this.count = count;        this.value = value;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public int getCount() {        return count;    }    public void setCount(int count) {        this.count = count;    }    public double getValue() {        return value;    }    public void setValue(double value) {        this.value = value;    }    @Override    public String toString() {        return "Buss{" +                "name='" + name + '\'' +                ", count=" + count +                ", value=" + value +                '}';    }}

Output

[Buss{name='a', count=10, value=0.3}, Buss{name='b', count=33, value=4.0}, Buss{name='c', count=25, value=2.1}]

如何根据两个字段排序
可以再 model里面 ，写一个类似的方法即可
下例，分组的key 就是 name+value

public String groupField() {        return getName()+"-"+getValue();    }