Access nested JSON object - Swift

I have three endpoints which all display an array of JSON data. I want to 'GET' the contents and populate it on a table view. how do i use struct or class methods to get a nested key between url links. I am trying to decode 'userId' in the posts url to display the users details in the users url.

These are the url links;

http://jsonplaceholder.typicode.com/posts

http://jsonplaceholder.typicode.com/users

http://jsonplaceholder.typicode.com/comments

I have given some JSON data but i would like to access the whole array.

http://jsonplaceholder.typicode.com/posts

[ {
  "userId": 1,
  "id": 1,
  "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
  "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et ***\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
  } ]

http://jsonplaceholder.typicode.com/users
[ {
  "id": 1,
  "name": "Leanne Graham",
  "username": "Bret",
  "email": "Sincere@april.biz",
  "address": {
  "street": "Kulas Light",
  "suite": "Apt. 556",
  "city": "Gwenborough",
  "zipcode": "92998-3874",
  "geo": {
  "lat": "-37.3159",
  "lng": "81.1496"
  }
  },
  "phone": "1-770-736-8031 x56442",
  "website": "hildegard.org",
  "company": {
  "name": "Romaguera-Crona",
  "catchPhrase": "Multi-layered client-server neural-net",
  "bs": "harness real-time e-markets"
  }
  } ]

http://jsonplaceholder.typicode.com/comments
[ {
  "postId": 1,
  "id": 1,
  "name": "id labore ex et quam laborum",
  "email": "Eliseo@gardner.biz",
  "body": "laudantium enim quasi est quidem magnam voluptate ipsam eos\ntempora quo necessitatibus\ndolor quam autem quasi\nreiciendis et nam sapiente accusantium"
  } ]

This is what i have so far -

import Foundation

var allUsers = [Users]()
var allPosts = [Posts]()

class Posts: Codable {
  let userId: Int
  let id: Int
  let title: String
  let body: String
}
class Users: Codable {
  let id: Int
  let name: String
  let username: String
}
let postURL = URL(string: "https://jsonplaceholder.typicode.com/posts")
let userURL = URL(string: "https://jsonplaceholder.typicode.com/users")
//let jsonData = try! Data(contentsOf: postURL!)
func parseJSON(){
  URLSession.shared.dataTask(with: postURL!) { (data, response, error) in
  guard let data = data else { print("error with data"); return }
  do {
  allPosts = try JSONDecoder().decode([Posts].self, from: data);
  //interupt the main thread and update the table with the retrieved data
  dump(allPosts)
  } catch let err {
  print("Error: ", err)
  }
  }.resume() // start the network call
  URLSession.shared.dataTask(with: userURL!) { (data, response, error) in
  guard let data = data else { print("error with data"); return }
  do {
  allUsers = try JSONDecoder().decode([Users].self, from: data);
  //interupt the main thread and update the table with the retrieved data
  dump(allUsers)
  } catch let err {
  print("Error: ", err)
  }
  }.resume() // start the network call
}

And i am calling the function parseJSON in view controller.