java 对json中list集合进行分组归类

有时候集合类型json数据，需要进一步按照类型进行分组加工，下面提供两种分组方式。

二、HashMap遍历分组

分组代码：

{
      ...
      ...
      ...
      ...
          //定义分组集合Map
          private Map<String, List<HomeEntity.DataBean>> groupMap = new HashMap<>();

          //遍历原始数据，根据code值进行分组
          for (HomeEntity.DataBean h : data) {
                String categoryCode = h.getCode();
                if (groupMap.containsKey(categoryCode)){
                    List<HomeEntity.DataBean> list = groupMap.get(categoryCode);
                    list.add(h);
                    groupMap.put(categoryCode, list);
                }else {
                    List<HomeEntity.DataBean> groupItemList = new ArrayList<>();
                    groupItemList.add(h);
                    groupMap.put(categoryCode, groupItemList );
          }

     ...
      ...
      ...
      ...
}

分组结果

  {"103":["17","19","21","23","25","27","29","31"],"100":["16","18","20","22","24","26","28","30"]}

二、jdk1.8 使用stream流进行分类

分组代码：

import com.alibaba.fastjson.JSON;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * @author czw
 */
public class Foo{
    private String name;
    private String type;
    private Double typeValue;
    private Integer count;

    public Foo(String name, String type, Double typeValue, Integer count) {
        this.name = name;
        this.type = type;
        this.typeValue = typeValue;
        this.count = count;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public Double getTypeValue() {
        return typeValue;
    }

    public void setTypeValue(Double typeValue) {
        this.typeValue = typeValue;
    }

    public Integer getCount() {
        return count;
    }

    public void setCount(Integer count) {
        this.count = count;
    }

    @Override
    public String toString() {
        return "Foo{" +
                "name='" + name + '\'' +
                ", type='" + type + '\'' +
                ", typeValue=" + typeValue +
                ", count=" + count +
                '}';
    }

    public static void main(String[] args) {
        List<Foo> fooList = new ArrayList<Foo>();
        fooList.add(new Foo("A","san",1.0,2))  ;
        fooList.add( new Foo("A","nas",13.0,1))  ;
        fooList.add(new Foo("B","san",112.0,3))  ;
        fooList.add(new Foo("C","san",43.0,5))  ;
        fooList.add(new Foo("B","nas",77.0,7))  ;
        List<List<Foo>> groupList = new ArrayList<>();
        fooList.stream()
                .collect(Collectors.groupingBy(Foo::getName,Collectors.toList()))
                .forEach((name,fooListByName)->{
                    groupList.add(fooListByName);
                });

        System.out.println(JSON.toJSONString(groupList));
    }
}

分组结果

[
    [{
        "count": 2,
        "name": "A",
        "type": "san",
        "typeValue": 1
    }, {
        "count": 1,
        "name": "A",
        "type": "nas",
        "typeValue": 13
    }],
    [{
        "count": 3,
        "name": "B",
        "type": "san",
        "typeValue": 112
    }, {
        "count": 7,
        "name": "B",
        "type": "nas",
        "typeValue": 77
    }],
    [{
        "count": 5,
        "name": "C",
        "type": "san",
        "typeValue": 43
    }]
]