JSONEncoder will encode instances of types that conform to the Codable typealias, as JSON objects. The following code illustrates how to do this:

let book1 = Book(name: "Mastering Swift 3", author: "Jon Hoffman", publisher: "Packt Publishing") 
 
let encoder = JSONEncoder() 
let data = try? encoder.encode(book1) 

This code starts off by creating an instance of the Book and JSONEncoder() types. Next the encode method of the JSONEncoder is used to encode the Book instance to a JSON object. If the encode method fails it will return nil; otherwise it will return an instance of a Data object. We can convert this object to an instance of the string type as shown in the following code:

if let data = data, let dataString = String(data: data, encoding: .utf8) { 
  print(dataString) 
} 

This code uses optional binding to JSON data to a string type and then prints it to the console. The default format for this JSONEncoder is to compact the JSON object; therefore, the output would look like this:

{"name":"Mastering Swift 3","author":"Jon Hoffman","publisher":"Packt Publishing"}

If we would like this output to be formatted, automatically, into a format that displays better, we can set the outputFormatting property of the JSONEncoder instance like this:

encoder.outputFormatting = .prettyPrinted 

With this property set the output now looks like this:

{
  "name" : "Mastering Swift 3",
  "author" : "Jon Hoffman",
  "publisher" : "Packt Publishing"
}  

We would encode an array of Book instances exactly like the previous example except that, instead of passing an instance of a Book type to the encoder; we pass an array of Book types. The following code illustrates this:

let book1 = Book(name: "Mastering Swift 3", author: "Jon Hoffman", publisher: "Packt Publishing") 
let book2 = Book(name: "Mastering Swift 4", author: "Jon Hoffman", publisher: "Packt Publishing") 
 
let books = [book1, book2] 
let encoder = JSONEncoder() 
let dataEncoder = try? encoder.encode(books) 
if let data = dataEncoder, let dataString = String(data: data, encoding: .utf8) { 
  print(dataString) 
} 

Now that we have seen how to encode JSON objects with the JSONEncoder type, let's look at how we can decode JSON objects with the JSONDecoder type.