java jdk1.8 使用stream流进行list 分组归类操作

 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)); } }

 [ [{ "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 }] ]

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

 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())) ));

 List damoformList = new ArrayList<>(); 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 */ 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());