java jdk1.8 使用stream流进行list 分组归类操作

2023-07-14 05:51:03 322

我就废话不多说了，大家还是直接看代码吧~

importcom.alibaba.fastjson.JSON;
importjava.util.ArrayList;
importjava.util.List;
importjava.util.stream.Collectors;
/**
*@authorczw
*/
publicclassFoo{
privateStringname;
privateStringtype;
privateDoubletypeValue;
privateIntegercount;
publicFoo(Stringname,Stringtype,DoubletypeValue,Integercount){
this.name=name;
this.type=type;
this.typeValue=typeValue;
this.count=count;
}
publicStringgetName(){
returnname;
}
publicvoidsetName(Stringname){
this.name=name;
}
publicStringgetType(){
returntype;
}
publicvoidsetType(Stringtype){
this.type=type;
}
publicDoublegetTypeValue(){
returntypeValue;
}
publicvoidsetTypeValue(DoubletypeValue){
this.typeValue=typeValue;
}
publicIntegergetCount(){
returncount;
}
publicvoidsetCount(Integercount){
this.count=count;
}
@Override
publicStringtoString(){
return"Foo{"+
"name='"+name+'\''+
",type='"+type+'\''+
",typeValue="+typeValue+
",count="+count+
'}';
}
publicstaticvoidmain(String[]args){
ListfooList=newArrayList();
fooList.add(newFoo("A","san",1.0,2));
fooList.add(newFoo("A","nas",13.0,1));
fooList.add(newFoo("B","san",112.0,3));
fooList.add(newFoo("C","san",43.0,5));
fooList.add(newFoo("B","nas",77.0,7));
List>groupList=newArrayList<>();
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：javajdk1.8的stream复杂和简单的分组

获取List对象中的某个参数时：

List>param=newArrayList<>();
Mapmap=newHashMap<>();
map.put("id","1213");
map.put("name","test");
ListstrList=param.stream().map(key->key.get("name")).collect(Collectors.toList());

简单参数分组：

ListdamoformList=newArrayList<>();
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。

ListdamoformList=newArrayList<>();
List>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
*/
Integersort1=o1.getValue().stream().anyMatch(item->item.getIsFlag()>0)?-1:1;
Integersort2=o2.getValue().stream().anyMatch(item->item.getIsFlag()>0)?-1:1;
returnsort1.compareTo(sort2);
})
.map(entry->{
Mapmap=Maps.newHashMapWithExpectedSize(2);
map.put("repairItemTypeName",entry.getKey());
/*
*这里排序，1排在前，0排在后
*/
ListdamoVOList=entry.getValue().stream()
.sorted(Comparator.comparingInt(o->(o.getIsFlag()*-1)))
.collect(Collectors.toList());
map.put("repairTypeList",itemDescFormList);
returnmap;
})
.collect(Collectors.toList());

以上这篇javajdk1.8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毛票票。

java jdk1.8 使用stream流进行list 分组归类操作

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