java stream 操作map根据key或者value排序的实现

阳光穿透心脏的1/2处 2023-10-06 22:21 33阅读 0赞

##### java8 使用lambda表达式和Stream APi 实现 list 集合转成map， 根据map的key 排序 和value 排序的实现 #####

public class Test02 {
        
        public static void main(String[] args) {
        
            List<FundBenchMarkInfo> fundBenchMarkList = new ArrayList<>();
            fundBenchMarkList.add(new FundBenchMarkInfo("2", new BigDecimal("123"), null));
            fundBenchMarkList.add(new FundBenchMarkInfo("5", new BigDecimal("12"), null));
            fundBenchMarkList.add(new FundBenchMarkInfo("1", new BigDecimal("8"), null));
            fundBenchMarkList.add(new FundBenchMarkInfo("7", new BigDecimal("8"), new BigDecimal("123345")));
            fundBenchMarkList.add(new FundBenchMarkInfo("8", new BigDecimal("3"), new BigDecimal("90")));
            fundBenchMarkList.add(new FundBenchMarkInfo("8", new BigDecimal("8"), null));
    
            // 把list 转成 map
            Map<String, FundBenchMarkInfo> collect = fundBenchMarkList.stream().collect(Collectors.toMap(t -> t.getIndexScod(), o -> o, (k1, k2) -> k1));
    
            // map 根据 key 排序
            LinkedHashMap<String, FundBenchMarkInfo> collect1 = collect.entrySet().stream()
                    .sorted(Map.Entry.comparingByKey())
                    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue,
                            LinkedHashMap::new));
    
            Map<String, Integer> unsortMap = new HashMap<>();
            unsortMap.put("z", 10);
            unsortMap.put("b", 5);
            unsortMap.put("a", 6);
            unsortMap.put("c", 20);
            unsortMap.put("d", 1);
            unsortMap.put("e", 7);
            unsortMap.put("y", 8);
            unsortMap.put("n", 99);
            unsortMap.put("g", 50);
            unsortMap.put("m", 2);
    
            // 根据key 排序
            //Alternative way to sort a Map by keys, and put it into the "result" map
            Map<String, Integer> result2 = new LinkedHashMap<>();
            unsortMap.entrySet().stream()
                    .sorted(Map.Entry.comparingByKey())
                    .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));
    
    
            // map 根据value 排序 根据value 进行降序排列
            LinkedHashMap<String, Integer> collect2 = unsortMap.entrySet().stream()
                    .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
                    .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,
                            (oldV, newV) -> oldV, LinkedHashMap::new));
    
            //Alternative way
            Map<String, Integer> result3 = new LinkedHashMap<>();
            unsortMap.entrySet().stream()
                    .sorted(Map.Entry.<String, Integer>comparingByValue().reversed())
                    .forEachOrdered(x -> result3.put(x.getKey(), x.getValue()));
    
    
        }
    }