Java使用Stream函数对集合进行分组

        List<Map<String,String>> list = new ArrayList<>();
        Map<String,String> map1 = new HashMap<>();
        map1.put("name", "卢俊义");
        map1.put("book", "水浒传");
        list.add(map1);
        Map<String,String> map2 = new HashMap<>();
        map2.put("name", "镇元子");
        map2.put("book", "西游记");
        list.add(map2);
        Map<String,String> map3 = new HashMap<>();
        map3.put("name", "林黛玉");
        map3.put("book", "红楼梦");
        list.add(map3);
        Map<String,String> map4 = new HashMap<>();
        map4.put("name", "黑旋风");
        map4.put("book", "水浒传");
        list.add(map4);
        Map<String,String> map5 = new HashMap<>();
        map5.put("name", "太上老君");
        map5.put("book", "西游记");
        list.add(map5);
        Map<String, List<Map<String, String>>> books = list.stream().collect(Collectors.groupingBy(i -> i.get("book")));
        books.forEach((k,v) -> {
            System.out.println(k);
            System.out.println(v.toString());
        });