如何在 Kotlin 中将地图和嵌套地图转换为字符串，反之亦然？

Question

我不知道如何将 HashMap 和嵌套 Hashmap 转换为字符串，反之亦然：

我使用 Room 将数据保存在本地数据库中。 "users" hashmap 是数据 class 的一个参数。要在Room数据库中保存这个参数"users"，我们必须将其转换为原始类型，如string、boolen、Integer等。Room不支持对象引用，所以type converters 是必需的。

val users = HashMap<String, HashMap<String, Any>>()

    val user1 = HashMap<String, Any>()
    user1["filter"] = 0
    user1["group"] = "groupId"
    user1["labelsVisibility"] = true
    user1["sort"] = 1
    user1["view"] = 3
    users["user1"] = user1

    val user2 = HashMap<String, Any>()
    user2["filter"] = 0
    user2["group"] = "groupId"
    user2["labelsVisibility"] = true
    user2["sort"] = 1
    user2["view"] = 3
    users["user2"] = user2

Answer 1

解决方案

可能有更好的方法来做到这一点，但它有效

使用特殊符号将 HashMap<String, HashMap<String, Any>> 转换为字符串 * + （符号在字符串中必须是唯一的）

 fun fromUsersPreferences(users: HashMap<String, HashMap<String, Any>>): String {
   var usersString = ""
   users.forEach {
     usersString = usersString.plus("${it.key}*${it.value}+")
   }
   usersString = usersString.dropLast(1)
   return usersString
 }

输出：

"user1*{filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}+user2*{filter=1, view=1, labelsVisibility=false, sort=0, group=groupId}"

将字符串转换为 HashMap<String, HashMap<String, Any>>

fun toUsersPreferences(users: String): HashMap<String, HashMap<String, Any>> {
 val usersMap = users.split("+").associateTo(HashMap()){
     val list = it.split("*")
     val userKey = list[0]
     val userValue = list[1].removeSurrounding("{", "}").split(", ").associateTo(HashMap()){
         val (key, value) = it.split("=")
         if (key.equals("group")) {
             Pair<String, Any>(key, value)
         } else if (key.equals("labelsVisibility")) {
             Pair<String, Any>(key, value.toBoolean())
         } else {
             Pair<String, Any>(key, value.toInt())
         }
     }

     Pair(userKey, userValue)
 }

 return usersMap
}

输出：

{user1={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}, user2={filter=1, view=1, labelsVisibility=false, sort=0, group=groupId}}

Answer 2

正如我之前在评论中所说，可以使用 Gson 库轻松完成：

// Configure Gson
val gson = GsonBuilder()
    // Using this strategy Gson first tries converting number to Long. 
    // If it fails (number is float), then it tries converting to Double
    .setObjectToNumberStrategy(ToNumberPolicy.LONG_OR_DOUBLE) 
    .create()

// Convert to JSON string
val jsonString = gson.toJson(users)
println("JSON => $jsonString")

// Store at Room as a string...
// Fetch later from Room as a string...

val type = object : TypeToken<HashMap<String, HashMap<String, Any>>>() {}.type
val fromJsonMap: HashMap<String, HashMap<String, Any>> = gson.fromJson(jsonString, type)

println("ORIGINAL MAP =>\n$users")
println("RESTORED MAP =>\n$fromJsonMap")

输出：

JSON => {
  "user1": {
    "filter": 0,
    "view": 3,
    "labelsVisibility": true,
    "sort": 1,
    "group": "groupId"
  },
  "user2": {
    "filter": 0,
    "view": 3,
    "labelsVisibility": true,
    "sort": 1,
    "group": "groupId"
  }
}

ORIGINAL MAP =>
{user1={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}, user2={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}}
RESTORED MAP =>
{user1={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}, user2={filter=0, view=3, labelsVisibility=true, sort=1, group=groupId}}

如您所见，原始地图 users 和恢复后的地图 fromJsonMap 完全相同。

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