集合(Map,List)分组：多属性进行分组

集合(Map,List)分组：多属性进行分组

 

一、List 实体字段分组

1. 根据单一字段进行分组：

Map<Integer, List<SomeEntity>> detailTypeMap = SomeEntityS.stream().collect(Collectors.groupingBy(SomeEntity::getSomeProperty));

2. 根据日期字段的 yyyy-MM 进行分组：

Map<String, List<SomeEntity>> monthMap = someEntityList.stream().collect(Collectors.groupingBy(p -> cn.hutool.core.date.DateUtil.format(p.getOrderTime(), "yyyy-MM")));

3.1 根据 Entigy多个字段，拼成一个 进行分组：

Map<String, Map<Integer, List<SomeEntity>>> someEntityGroup = someEntityList.stream().collect(Collectors.groupingBy(SomeEntity::getSomePropertyOne, Collectors.groupingBy(SomeEntity::getSomePropertyTwo)));

3.2 根据 Entigy多个字段，分开进行分组：

Map<Integer, Map<Integer, Map<Integer, List<SomeEntity>>>> someEntityGroup = someEntityList.stream().collect(
Collectors.groupingBy(SomeEntity::getSomePropertyOne,
Collectors.groupingBy(SomeEntity::getSomePropertyTwo,
Collectors.groupingBy(SomeEntity::getSomePropertyThree))));

3.3 根据 多字段分组，引入一个包括分组字段的对象，进行分组：

    @Data
    @Builder
    @EqualsAndHashCode
    @AllArgsConstructor
    @NoArgsConstructor
    public class UseGroupEntity {

        /** 某属性 */
        private Integer somePropertyOne;

        /** 某属性 */
        private Integer somePropertyTwo;
        
        /** 某属性 */
        private String somePropertyThree;

    }
    
    if(CollectionUtils.isNotEmpty(someEntityList)) {
        someEntityGroup = someEntityList.stream().collect(Collectors.groupingBy(entity -> {
            return UseGroupEntity.builder().shopId(entity.getSomePropertyOne()).contractInfoId(entity.getSomePropertyTwo()).settleWay(entity.getSomePropertyThree()).build();
        }));
    }

二、Map 多个key进行分组
4. 根据 Map中的多个字段组合进行分组：
【写法1】：

        Map<String, List<Map<String, String>>> mapListGroup = new HashMap();
        mapListGroup = someMapList.stream().collect(Collectors.groupingBy(dataMap -> {
            String groupByField = "";
            StringBuilder groupKey = new StringBuilder();
            if(groupByBussTypeField.contains(",")){        // groupByBussTypeField 以逗号分隔的多分组字段的配置值 例 t1.name,t1.age,t2.score 
                String[] fields = groupByBussTypeField.split(",");
                for(String field : fields){
                    String groupField = field.substring(field.indexOf(".") + 1);    // 将 t1.name,t1.age,t2.score 的点号前的前缀切去，获得单独的属性 name 和 age 和 score
                    groupKey.append(""").append(groupField).append(""").append(":").append(""").append(String.valueOf(dataMap.get(groupField))).append(""");
                }
                groupByField = groupKey.toString();
            }else{
                groupByField = String.valueOf(dataMap.get(groupByBussTypeField.substring(groupByBussTypeField.indexOf(".") + 1)));
            }
            return groupByField;
        }));

【写法2】：

        Map<String, List<Map<String, String>>> voucherGroup = someMapList.stream().collect(Collectors.groupingBy((e -> fetchGroupKey(someEntityProperties, e))));
        
        private String fetchGroupKey(List<SomeEntityProperty> someEntityProperties, Map<String, String> dataMap){
            // log.debug("fetchGroupKey 入参：someEntityProperties:{},dataMap:{}", JSON.toJSONString(someEntityProperties), JSON.toJSONString(dataMap));
            if(CollectionUtils.isEmpty(collection)){
                String errorMsg = "数据为为空，请核查！";
                log.error(errorMsg);
                throw new RuntimeException(errorMsg);
            }
            StringBuilder groupKey = new StringBuilder();
            someEntityProperties.forEach(someEntityProperty -> {
                String fieldNameByField = someEntityProperty.getName();
                groupKey.append(""").append(fieldNameByField).append(""").append(":").append(""").append(String.valueOf(dataMap.get(fieldNameByField))).append(""");
            });
            // log.debug("依多属性字段分组，分组依据为：{}", groupKey.toString());
            return groupKey.toString();
        }