ajax请求相关方法

jdk8分组返回的map，value除了是List，还可以是多种类型。

示例：

    public static void main(String[] args) {
        List<Map<String, Object>> list = Arrays.asList(
                ImmutableMap.of("id", 1, "name", "zhangsan", "city", "henan"),
                ImmutableMap.of("id", 2, "name", "lisi", "city", "hebei"),
                ImmutableMap.of("id", 3, "name", "wangwu", "city", "tianjin"),
                ImmutableMap.of("id", 4, "name", "maliu", "city", "henan")
        );

        Map<Object, List<Map<String, Object>>> map = list.stream().collect(Collectors.groupingBy(p -> p.get("city")));
        System.out.println(map);

        Map<Object, Set<Object>> map0 = list.stream().collect(Collectors.groupingBy(p -> p.get("city"), Collectors.mapping(p -> p.get("city"), Collectors.toSet())));
        System.out.println(map0);

        Map<Object, Long> ss = list.stream().collect(Collectors.groupingBy(p -> p.get("city"), Collectors.counting()));
        System.out.println(ss);
    }

重点就是利用Collectord