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;
/**
 * @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 = http://www.cppcns.com/ruanjian/java/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="http://www.cppcns.com/ruanjian/java/+ 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));
  }
}

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

简单参数分组:

List<DamoForm> damoformList = new ArrayList<>();
Map<String, Map<String, List<DamoForm>>> 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<DamoForm> damoformList = new ArrayList<>();
List<Map<String, Object>> result = damoformList.stream()
     .collect(Collectors.groupingBy(DamoForm::getPartClass))
     .entrySet()
     .stream()
     .sorted((o1, o2) -> {
       /*
        * 这里排序,任何有1的排在前,全部是0排在后
        */
        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<String, Object> map = Maps.newHashMapWithExpectedSize(2);
        map.put("repairItemTypeName", entry.getKey());
          /*
           * 这里排序,1排在前,0排在后
           */
          List<DamoVO> damoVOList = entry.getValue().stream()
              .sorted(Comparator.comparingInt(o -> (o.getIsFlag() * -1)))
              .collect(Collectors.toList());
          map.put("repairTypeList", itemDescFormList);
          return map;
     })
     .collect(Collectors.toList());

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java jdk1.8 使用stream流进行list 分组归类操作

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