stream 分类变成多层map

布满荆棘的人生 2022-12-11 09:17 418阅读 0赞

按照组合键分类  
    1，list分类 用stream分类，自动变成map,可以组合属性分类 直接用groupb有，连用几个分几层，也可逐级分类，用一级分类一级，不必一步到位  
      
    //    private static String fetchGroupKeyDaypart(String channelCode, String dateTypeCode, TemplateDimension templateDimension) \{  
//        return channelCode + "\#" + dateTypeCode + "\#" + templateDimension.getDaypartCode();  
//    \}

List<TemplateDimension> mapDateTypeValue = dateType.getValue();

Map<String, List<TemplateDimension>> groupByDaypart = mapDateTypeValue.stream().filter(e -> dayType.equals(e.getDateTypeCode())).collect(Collectors.groupingBy(e -> fetchGroupKeyDaypart(mapKey, dayType, e)));

两层map转化

Map<String, Map<String, List<ProductStrikeoutPrice>>> productStrikeoutPriceTierMap = new HashMap<>(PcmConstants.HASH\_MAP\_SIZE);  
 List<ProductStrikeoutPrice>  productStrikeoutPrices =  productStrikeoutPriceMapper.selectListByProductStrikeout(productDetailStrikeoutAll,demissionCategory.getDataVersion());  
                if (null != productStrikeoutPrices && productStrikeoutPrices.size() > 0) \{  
                    productStrikeoutPriceTierMap = productStrikeoutPrices.stream().collect(Collectors.groupingBy(ProductStrikeoutPrice::getProductCode, Collectors.groupingBy(ProductStrikeoutPrice::getPriceTierCode)));  
                \}

2，多层分类，map套map //按照模板分类所有维度--list中的元素是map---即可对map分类---list分类自动变成map----多个map间按照key合并

flatMap对集合进行抽出部分的裁剪，当每次抽出的是list用flagMap,否则用map
    Map<TemplateUsed, TemplateDimension> m1 = new HashMap<>();
        m1.put("A", 1l);
        m1.put("B", 100l);
    
        Map<TemplateUsed, TemplateDimension> m2 = new HashMap<>();
        m2.put("A", 10l);
        m2.put("B", 20l);
        m2.put("C", 100l);
    
        List<Map<TemplateUsed, TemplateDimension>> beforeFormatting = new ArrayList<>();
        beforeFormatting.add(m1);
        beforeFormatting.add(m2);

Map<TemplateUsed, List<Map<TemplateDimension, TemplateDimension>>> resultDimensionMap = beforeFormatting.stream()  
                .flatMap(x -> x.entrySet().stream())  //---这里转化成map的遍历  
                .collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.mapping(Map.Entry::getValue, Collectors.toList())));//用map的操作方法  
                list分类自动变为map

3,map转list  
HashMap<String, Integer> map = new HashMap<>();  
        map.put("mayun",2000);  
        map.put("mahuateng",1200);  
        map.put("liuqiangdong",700);  
        List<Account> collect = map.entrySet().stream().map(en -> new Account(en.getKey(), en.getValue())).collect(Collectors.toList());  
        collect.stream().forEach(n-> System.out.println(n));

//用这中去重方法空key会报错空指针变成""用的时候在去掉""即可  
         List<CategoryDetailAllVO> categorTagDetailAllDis = categoryDetailAlls.stream().filter(distinctByKey(p -> (p.getTagCode() == null ? "" : p.getTagCode())))  
                                                .collect(Collectors.toList());  
                                                  
                                                public static <T> Predicate<T> distinctByKey(Function<? super T, Object> keyExtractor) \{  
        Map<Object, Boolean> map = new ConcurrentHashMap<>();  
        return t -> map.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;  
    \}