如何将map列表转换为哈希数组

Question

我使用Java为我的应用程序。这是我的输入数据。

[{
"id": 1,
"firstname": "one",
"lastname": "1"
},
{
"id": 2,
"firstname": "two",
"lastname": "2"
},
{
"id": 3,
"firstname": "three",
"lastname": "3"
}
]

我想把上面的输入转换成下面的输出。我怎样才能以有效的方式实现以下输出?

{
["id", "firstname", "lastname"], [1, "one", "1"], [2, "two", "2"], [3, "three", "3"]
}

更新:

我试过下面的方法。但结果如下

预期:

result => {[lastname, id, firstname]=[[1, 1, one], [2, 2, two], [3, 3, three]]}

实际:

结果=比;{[lastname、id、名],[1,1,],[2 2 2],[3,3,3]}

代码:

Map<String, Object> one = Map.of("id", 1, "firstname", "one", "lastname", "1");
Map<String, Object> two = Map.of("id", 2, "firstname", "two", "lastname", "2");
Map<String, Object> three = Map.of("id", 3, "firstname", "three", "lastname", "3");
ArrayList<Map<String,Object>> list = new ArrayList<>();
list.add(one);
list.add(two);
list.add(three);
MultiValueMap<Object, Object> result = new LinkedMultiValueMap<>();
Set<String> strings = list.get(0).keySet();
ArrayList<Object> objects = new ArrayList<>();
for(Map<String,Object> map: list) {
objects.add(map.values());
}
result.put(strings, objects);

Answer 1

可以将输入的JSON读入具有相同键集的映射列表data，并将该列表转换为对象数组列表，该列表的第一个元素为映射的键。

因此，首先创建字段名数组，将其转换为Stream，然后与从data列表中每个映射的值中检索到的Stream<Object[]>合并:

// using Jackson JSON to read the input
ObjectMapper mapper = new ObjectMapper();
String input = "[{"id":1, "firstname":"First", "lastname": "Last"}]";
List<Map<String, Object>> data = mapper.readValue(input, new TypeReference<>() {});
List<Object[]> output = Stream.concat(
Stream.<Object[]>of(data.get(0).keySet().toArray()),
data.stream().map(m -> m.values().toArray())
)
.collect(Collectors.toList());
System.out.printf("Result: {%nt%s%n}%n", 
output.stream().map(Arrays::toString).collect(Collectors.joining(", ")));
System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(output));

输出:

Result: {
[id, firstname, lastname], [1, First, Last]
}
[ [ "id", "firstname", "lastname" ], [ 1, "First", "Last" ] ]

---

或者类似地，结果可能是基于map的keySet()和values的原始集合列表，可以这样创建:

List<Collection> result = Stream.concat(
Stream.of(data.get(0).keySet()),
data.stream().map(Map::values)
).collect(Collectors.toList());