java jdk1.8 使用stream流进行list 分组归类操作

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 = 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

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

.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 map = Maps.newHashMapWithExpectedSize(2);

map.put("repairItemTypeName", entry.getKey());

/*

* 这里排序，1排在前，0排在后

*/

List 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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