List转Map的几种方式

最新推荐文章于 2024-03-31 18:03:42 发布

原创最新推荐文章于 2024-03-31 18:03:42 发布

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前言需求：

需要记录下之前List的转Map的使用方法，感觉好记性不如烂笔头，记录下之前使用过的List转成Map的实现java逻辑代码

 RuleExpress ruleExpress = new RuleExpress();
        ruleExpress.setNewsType(1);
        List<RuleExpress> commonRuleExpressList = ruleExpressDao.listRuleExpresss(ruleExpress);
        Map<String, List<RuleExpress>> commonRuleExpressMap = commonRuleExpressList.stream().collect(Collectors.groupingBy(RuleExpress::getType, LinkedHashMap::new, Collectors.toList()));
        ContantData.setCommonNewsRuleExpressMap(commonRuleExpressMap);
        ruleExpress.setNewsType(2);
        List<RuleExpress> fastNewsRuleExpressList = ruleExpressDao.listRuleExpresss(ruleExpress);
        Map<String, List<RuleExpress>> fastNewsRuleExpressMap = fastNewsRuleExpressList.stream().collect(Collectors.groupingBy(RuleExpress::getType, LinkedHashMap::new, Collectors.toList()));
        ContantData.setFastNewsRuleExpressMap(fastNewsRuleExpressMap);

Map<Integer, List<Student>> commonMap = list.stream().collect(Collectors.groupingBy(Student::getNo, LinkedHashMap::new, Collectors.toList()));

            Student noMax = list.stream().max(Comparator.comparing(Student::getNo)).get();
            List<Student>   maxList=commonMap.get(noMax.getNo());
            System.out.println("------最大的列表---------");
            System.out.println(maxList.toString());
            System.out.println("---------------");

  @Override
    public Map<Integer, Map<String, String>> getNewsRangeConfig() {
        QueryWrapper<TbmNewsRangeConfig> queryWrapper = new QueryWrapper();
        queryWrapper.orderByAsc("id");
        List<TbmNewsRangeConfig> tbmNewsRangeConfigList = tbmNewsRangeConfigMapper.selectList(queryWrapper);
        Map firstLevelCodeMap = tbmNewsRangeConfigList.stream().collect(Collectors.groupingBy(TbmNewsRangeConfig::getFirstLevelCode, LinkedHashMap::new, Collectors.toMap(TbmNewsRangeConfig::getFirstLevelCode, TbmNewsRangeConfig::getFirstLevelName, (k1, k2) -> k1)));
        Map secondLevelCodeMap = tbmNewsRangeConfigList.stream().collect(Collectors.groupingBy(TbmNewsRangeConfig::getSecondLevelCode, LinkedHashMap::new, Collectors.toMap(TbmNewsRangeConfig::getSecondLevelCode, TbmNewsRangeConfig::getSecondLevelName, (k1, k2) -> k1)));
        Map thirdLevelCodeMap = tbmNewsRangeConfigList.stream().collect(Collectors.groupingBy(TbmNewsRangeConfig::getThirdLevelCode, LinkedHashMap::new, Collectors.toMap(TbmNewsRangeConfig::getThirdLevelCode, TbmNewsRangeConfig::getThirdLevelName, (k1, k2) -> k1)));
        Map fourthLevelCodeMap = tbmNewsRangeConfigList.stream().collect(Collectors.groupingBy(TbmNewsRangeConfig::getFourthLevelCode, LinkedHashMap::new, Collectors.toMap(TbmNewsRangeConfig::getFourthLevelCode, TbmNewsRangeConfig::getFourthLevelName, (k1, k2) -> k1)));

        Map<Integer, Map<String, String>> result = new LinkedHashMap<>();
        result.put(1, firstLevelCodeMap);
        result.put(2, secondLevelCodeMap);
        result.put(3, thirdLevelCodeMap);
        result.put(4, fourthLevelCodeMap);
        return result;
    }