如何在没有case类的情况下解析JSON-Scala

Question

我有一个JSON，它可以随时间变化，用例class可能不可信，因为每次JSON更改时我都需要更改它的结构。

例如，如果我有这样的JSON：

val json= """{
  "accounts": [
  { "emailAccount": {
    "accountName": "YMail",
    "username": "USERNAME",
    "password": "PASSWORD",
    "url": "imap.yahoo.com",
    "minutesBetweenChecks": 1,
    "usersOfInterest": ["barney", "betty", "wilma"]
  }},
  { "emailAccount": {
    "accountName": "Gmail",
    "username": "USER",
    "password": "PASS",
    "url": "imap.gmail.com",
    "minutesBetweenChecks": 1,
    "usersOfInterest": ["pebbles", "bam-bam"]
  }}
  ]
}"""

我能用之类的东西访问它吗

val parsedJSON = parse(json)
parsedJSON.accounts(0).emailAccount.accountName

Answer 1

circe的光学模块几乎完全支持您所要求的语法：

import io.circe.optics.JsonPath.root
val accountName = root.accounts.at(0).emailAccount.accountName.as[String]

然后，如果您有这个JSON值（我使用cire的JSON文本支持，但您也可以使用io.circe.jawn.parse（解析函数）解析字符串，以获得您正在使用的Json值）：

import io.circe.Json, io.circe.literal._
val json: Json = json"""{
  "accounts": [
  { "emailAccount": {
    "accountName": "YMail",
    "username": "USERNAME",
    "password": "PASSWORD",
    "url": "imap.yahoo.com",
    "minutesBetweenChecks": 1,
    "usersOfInterest": ["barney", "betty", "wilma"]
  }},
  { "emailAccount": {
    "accountName": "Gmail",
    "username": "USER",
    "password": "PASS",
    "url": "imap.gmail.com",
    "minutesBetweenChecks": 1,
    "usersOfInterest": ["pebbles", "bam-bam"]
  }}
  ]
}"""

你可以这样尝试访问帐户名：

scala> accountName.getOption(json)
res0: Option[String] = Some(YMail)

因为circe-optics是在Monocle上构建的，所以你可以获得一些其他不错的功能，比如不可变的更新：

scala> accountName.modify(_.toLowerCase)(json)
res2: io.circe.Json =
{
  "accounts" : [
    {
      "emailAccount" : {
        "accountName" : "ymail",
        ...

等等。

---

更新：circe被设计成模块化的，所以你只需要"支付"你需要的零件。上面的例子期望类似于SBT的以下设置：

scalaVersion := "2.11.8"
val circeVersion = "0.4.1"
libraryDependencies ++= Seq(
  "io.circe" %% "circe-core" % circeVersion,
  "io.circe" %% "circe-jawn" % circeVersion,
  "io.circe" %% "circe-literal" % circeVersion,
  "io.circe" %% "circe-optics" % circeVersion
)

…或者对于Maven：

<dependency>
  <groupId>io.circe</groupId>
  <artifactId>circe-core_2.11</artifactId>
  <version>0.4.1</version>
</dependency>
<dependency>
  <groupId>io.circe</groupId>
  <artifactId>circe-jawn_2.11</artifactId>
  <version>0.4.1</version>
</dependency>
<dependency>
  <groupId>io.circe</groupId>
  <artifactId>circe-literal_2.11</artifactId>
  <version>0.4.1</version>
</dependency>
<dependency>
  <groupId>io.circe</groupId>
  <artifactId>circe-optics_2.11</artifactId>
  <version>0.4.1</version>
</dependency>