javastreammap分组_java8Stream对ListMap的分组合并操作public classGamer47 {public static voidmain(String[] args) {//将List变成⼀个map
mergeListmapToOnemap(null);//将两个List合并成⼀个List，“name”为map的key
mergeTwoListmapToOneListmap(null,null,"name");//对List分组统计
summaryGroup();
}/**
* 对List 进⾏分组合并，按某个相同的key进⾏合并，并sum某个key，
* 类似单表group by 功能*/
public static voidsummaryGroup(){
Map m1=new HashMap<>();
Map m11=new HashMap<>();
Map m12=new HashMap<>();
List> list =new ArrayList<>();
List> result =new ArrayList<>();
m1.put("aa", 11);
m1.put("bb", "xm");
m1.put("cc", 122);
m1.put("dd", 122);
m11.put("aa", 12);
m11.put("bb","xm");
m11.put("cc", 10);
m11.put("dd", 122);
m12.put("aa", 13);
m12.put("bb", "zs");
m12.put("cc", 31);
m12.put("dd", 122);
list.add(m1);
list.add(m11);
list.add(m12);//按bb进⾏分组统计
Map>> glist = list.stream().upingBy(e -> e.get("bb").toString()));
glist.forEach((k,slist)->{
Map nmap=new HashMap<>();
IntSummaryStatistics sumcc= slist.stream().collect(Collectors.summarizingInt(e->Integer.("cc").toString())));
nmap.put("aa", (0).get("dd"));
nmap.put("bb", (0).get("dd"));
nmap.put("cc", Sum());//求和
nmap.put("counts", slist.size());//计算
nmap.put("dd", (0).get("dd"));
result.add(nmap);
});
System.out.println("--------summaryGroup-------------"); result.forEach(x->{
System.out.println(x);
});
}/**
* list的中map合并为⼀个map，即List 转为Map newMap,
* newMap中包含了list中每个map的key与value*/
public static void mergeListmapToOnemap(Listlistmap){ Map h1 = new HashMap<>();
h1.put("12","fdsa");
h1.put("123","fdsa");
h1.put("124","fdsa");
h1.put("125","fdsa");
Map h2 = new HashMap<>();
h2.put("h12","fdsa");
h2.put("h123","fdsa");
h2.put("h124","fdsa");
h2.put("h125","fdsa");
Map h3 = new HashMap<>();
h3.put("h12","fdsa");
h3.put("h3123","fdsa");
h3.put("h3124","fdsa");
h3.put("h3125","fdsa");
List> lists = new ArrayList<>();
lists.add(h1);
lists.add(h2);
lists.add(h3);//⽤java 8 把lists⾥⾯的map合并成⼀个新的map: Map haNew = new HashMap<>(); //包含了h1,h2,h3的内容
Map merged =lists.stream()
.map(Map::entrySet)
.flatMap(Set::stream)
.distinct()
.Map(Map.Entry::getKey, Map.Entry::getValue));
Stream mlist =lists.stream().map(Map::entrySet);
Stream fmlist =lists.stream()
.map(Map::entrySet)
.flatMap(Set::stream);java stream
System.out.println("merged="+merged);
}/**
* 两个list《map》中的map合并为⼀个list《map》，新的list中的每个map包含了之前的两个listmap的key*/ public static void mergeTwoListmapToOneListmap(List list1,Listlist2,final String mergeKey){ List> lists = new ArrayList<>();
List> lists1 = new ArrayList<>();
List> lists2 = new ArrayList<>();//--------------lists1--------------------
Map h1 = new HashMap<>();
h1.put("name","fdsa0");
h1.put("2","fdsa0");
h1.put("3","fdsa0");
h1.put("4","fdsa0");
Map h2 = new HashMap<>();
h2.put("name","fdsa00");
h2.put("2","fdsa00");
h2.put("3","fdsa00");
h2.put("4","fdsa00");
lists1.add(h1);
lists1.add(h2);//--------------lists2--------------------
Map h3 = new HashMap<>();
h3.put("name","fdsa0");
h3.put("21","fdsa1");
h3.put("31","fdsa1");
h3.put("41","fdsa1");
Map h4 = new HashMap<>();
h4.put("name","fdsa00");
h4.put("21","fdsa2");
h4.put("31","fdsa2");
h4.put("41","fdsa2");
lists2.add(h3);
lists2.add(h4);//测试//mergeKey="name";
lists1.parallelStream().forEach(x->{
Map y2 = lists2.parallelStream().filter(y-&(mergeKey).toString().(mergeKey).toString())) .findFirst().get();
List> sublist =Arrays.asList(x,y2);
Map merged =sublist.stream()
.map(Map::entrySet)
.flatMap(Set::stream)
.distinct()
.Map(Map.Entry::getKey, Map.Entry::getValue));
lists.add(merged);
});
System.out.println("----------list--mergetMap---------");
lists.forEach(x->{
System.out.println(x);
});
}

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