javajdk1.8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;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
}
public Double getTypeValue() {
return typeValue;
}
public void setTypeValue(Double typeValue) {
}
public Integer getCount() {
return count;
}
public void setCount(Integer 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>();
java streamfooList.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()
.upingBy(Foo::List()))
.forEach((name,fooListByName)->{
groupList.add(fooListByName);
});
System.out.JSONString(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 -&("name")).List());
简单参数分组：
List<DamoForm> damoformList = new ArrayList<>();
Map<String, Map<String, List<DamoForm>>> collect = damoformList.stream()
.upingBy(DamoForm::getId()))
.
entrySet()
.stream()
.Map(
entry -> Key(),
entry -> Value().stream().upingBy(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()
.upingBy(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 -> IsFlag() > 0) ? -1 : 1;
Integer sort2 = o2.getValue().stream().anyMatch(item -> IsFlag() > 0) ? -1 : 1;
return sort1pareTo(sort2);
})
.map(entry -> {
Map<String, Object> map = wHashMapWithExpectedSize(2);
map.put("repairItemTypeName", Key());
/*
* 这⾥排序，1排在前，0排在后
*/
List<DamoVO> damoVOList = Value().stream()
.sorted(ComparatorparingInt(o -> (o.getIsFlag() * -1)))
.List());
map.put("repairTypeList", itemDescFormList);
return map;
})
.List());
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。

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