从 JSON 中提取字段

Question

我有一个 JSON 形式的对象：

{"apps":{"app":[{"id":"application_1481567788061_0002","user":"root","name":"wordcount.py","queue":"default","state":"FAILED","finalStatus":"FAILED","progress":0.0,"trackingUI":"History", "diagnostics":"Application application_1481567788061_0002 failed 2 times due to AM Container for appattempt_1481567788061_0002_000002 exited with  exitCode: 255\nFor more detailed output, check application tracking page:http://sandbox:8088/proxy/application_1481567788061_0002/Then, click on links to logs of each attempt.\nDiagnostics: Exception from container-launch.\nContainer id: container_1481567788061_0002_02_000001\nExit code: 255\nStack trace: ExitCodeException exitCode=255: \n\tat org.apache.hadoop.util.Shell.runCommand(Shell.java:538)\n\tat org.apache.hadoop.util.Shell.run(Shell.java:455)\n\tat org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:715)\n\tat org.apache.hadoop.yarn.server.nodemanager.DefaultContainerExecutor.launchContainer(DefaultContainerExecutor.java:211)\n\tat org.apache.hadoop.yarn.server.nodemanager.containermanager.launcher.ContainerLaunch.call(ContainerLaunch.java:302)\n\tat org.apache.hadoop.yarn.server.nodemanager.containermanager.launcher.ContainerLaunch.call(ContainerLaunch.java:82)\n\tat java.util.concurrent.FutureTask.run(FutureTask.java:262)\n\tat java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)\n\tat java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)\n\tat java.lang.Thread.run(Thread.java:744)\n\n\nContainer exited with a non-zero exit code 255\nFailing this attempt. Failing the application.","clusterId":1481567788061,"applicationType":"SPARK","applicationTags":"","startedTime":1481568051052,"finishedTime":1481568079289,"elapsedTime":28237,"amHostHttpAddress":"sandbox:8042","allocatedMB":-1,"allocatedVCores":-1,"runningContainers":-1,"memorySeconds":55598,"vcoreSeconds":27,"preemptedResourceMB":0,"preemptedResourceVCores":0,"numNonAMContainerPreempted":0,"numAMContainerPreempted":0},{"id":"application_1481567788061_0001","user":"root","name":"pi.py","queue":"default","state":"FINISHED","finalStatus":"SUCCEEDED","progress":100.0,"trackingUI":"History","diagnostics":"","clusterId":1481567788061,"applicationType":"SPARK","applicationTags":"","startedTime":1481567853324,"finishedTime":1481567888648,"elapsedTime":35324,"amContainerLogs":"http://sandbox:8042/node/containerlogs/container_1481567788061_0001_01_000001/root","amHostHttpAddress":"sandbox:8042","allocatedMB":-1,"allocatedVCores":-1,"runningContainers":-1,"memorySeconds":138031,"vcoreSeconds":66,"preemptedResourceMB":0,"preemptedResourceVCores":0,"numNonAMContainerPreempted":0,"numAMContainerPreempted":0}]}}

我想从中提取一个List[Application]，其中应用程序是：

case class Application(id: String, user: String, name: String)

我导入了 spray-json。如果 message 是一个包含 JSON 组件的字符串，我想做这样的事情：

  val json: JsValue = message.parseJson
  val jobsJson = json.first.first
  val jobs = jobsJson.map(job => Application(job(0), job(1), job(2)))

但这不正确，因为我不能使用 json.first。

那么如何提取嵌套在 JSON 对象中的字段呢？是否有另一个库可以让事情变得更简单？

Answer 1

注意： 这个答案是关于 play-json 而不是 spray-json 图书馆。

您应该能够使用 \ 或 \ 从 json 对象中获取数据单斜杠将在下一个杠杆中查找您要查找的内容，而双斜杠将查看整个对象。假设您将以下 json 存储在名为 obj 的变量中：

{"foo":"bar","num":3, "value":{"num":4}}

使用 obj\num 你只会得到 3。但是使用 obj\num 你会得到包含 3 和 4 的迭代器。

尝试 this link 了解更多信息。

从 JSON 中提取字段

Extract fields from JSON

json

scala

spray-json