java jdk1.8 使用stream流进行list 分组归类操作

我就废话不多说了，大家还是直接看代码吧~

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

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 fooList = new ArrayList();
    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> groupList = new ArrayList<>();
    fooList.stream()
 .collect(Collectors.groupingBy(Foo::getName,Collectors.toList()))
 .forEach((name,fooListByName)->{
   groupList.add(fooListByName);
 });
    System.out.println(JSON.toJSonString(groupList));
  }
}

输出结果

[
  [{
    "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
  }]
]

补充知识：java jdk1.8的stream复杂和简单的分组

获取List对象中的某个参数时：

List> param = new ArrayList<>();
Map map = new HashMap<>();
map.put("id","1213");
map.put("name","test");
List strList = param.stream().map(key ->key.get("name")).collect(Collectors.toList());

简单参数分组：

List damoformList = new ArrayList<>();
Map>> collect = damoformList.stream()
 .collect(Collectors.groupingBy(DamoForm::getId()))
 .entrySet()
 .stream()
 .collect(Collectors.toMap(
     entry -> entry.getKey(),
     entry -> entry.getValue().stream().collect(Collectors.groupingBy(DamoForm::getName()))
 ));

针对List复杂排序，多个条件进行排序：

应用场景：针对List中某个字段的数据进行双重倒序的方式排序，代码有点复杂，不明白的可以留言。

List damoformList = new ArrayList<>();
List> result = damoformList.stream()
     .collect(Collectors.groupingBy(DamoForm::getPartClass))
     .entrySet()
     .stream()
     .sorted((o1, o2) -> {

 Integer sort1 = o1.getValue().stream().anyMatch(item -> item.getIsFlag() > 0) ? -1 : 1;
 Integer sort2 = o2.getValue().stream().anyMatch(item -> item.getIsFlag() > 0) ? -1 : 1;
 return sort1.compareTo(sort2);
     })
     .map(entry -> {
 Map map = Maps.newHashMapWithExpectedSize(2);
 map.put("repairItemTypeName", entry.getKey());
   
   List damoVOList = entry.getValue().stream()
.sorted(Comparator.comparingInt(o -> (o.getIsFlag() * -1)))
.collect(Collectors.toList());
   map.put("repairTypeList", itemDescFormList);
   return map;
     })
     .collect(Collectors.toList());

以上这篇java jdk1.8 使用stream流进行list 分组归类操作就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持考高分网。