java List<Map<String, Object>> 转成Map<String,List<String>>

Question

List<Map<String, Object>> map = new ArrayList<Map<String,Object>>();
    Map<String, Object> mapList = new HashMap<>();
    mapList.put("xxx", 1);
    Map<String, Object> mapList2 = new HashMap<>();
    mapList2.put("xxx", 2);
    Map<String, Object> mapList3 = new HashMap<>();
    mapList3.put("xxx", 3);
    map.add(mapList2);
    map.add(mapList3);
    map.add(mapList3);
    转为Map<String,List<String>>  键是xxx，值是1，2，3

Answer 1

     * list转map
     * <p>
     * Map<String,List<String>>
     */
    private Map<String, List<String>> convert(List<Map<String, Object>> list) {
        // 这是要返回的map对象
        HashMap<String, List<String>> map = new HashMap<>();

        // 对应的list
        ArrayList<String> mapList = new ArrayList<>();
        String key = null;
        // 遍历list
        for (Map<String, Object> item : list) {
            // 取出item中所有对应的value
            for (String itemKey : item.keySet()) {
                // 因为key都是xxx，所以直接去第一个map的可以就可以了
                if (key == null) {
                    key = itemKey;
                }
                mapList.add(String.valueOf(item.get(itemKey)));
            }
        }
        // 遍历结束
        map.put(key, mapList);
        return map;
    }

这个其实不难，主要是看map的keyset等api的用法