How can I easily see the JSON output from my objects that conform to the `Codable` Protocol

Question

I deal with lots of objects that I serialize/deserialize to JSON using the Codable protocol.

It isn't that hard to create a JSONEncoder, set it up to pretty-print, convert the object to JSON, and then convert that to a string, but seems like a lot of work. Is there a simple way to say "please show me the JSON output for this object?"

EDIT:

Say for example I have the following structures:

struct Foo: Codable {
    let string1: String?
    let string2: String?
    let date: Date
    let val: Int
    let aBar: Bar
}

struct Bar: Codable {
    let name: String
}

And say I've created a Foo object:

let aBar = Bar(name: "Fred")
let aFoo = Foo(string1: "string1", string2: "string2", date: Date(), val: 42, aBar: aBar)

I could print that with a half-dozen lines of custom code:

let encoder = JSONEncoder()
encoder.outputFormatting = .prettyPrinted
guard let data = try? encoder.encode(aFoo),
    let output = String(data: data, encoding: .utf8)
    else { fatalError( "Error converting \(aFoo) to JSON string") }
print("JSON string = \(output)")

Which would give the output:

JSON string = {
  "date" : 557547327.56354201,
  "aBar" : {
    "name" : "Fred"
  },
  "string1" : "string1",
  "val" : 42,
  "string2" : "string2"
}

I get tired of writing the same half-dozen lines of code each time I need it. Is there an easier way?

Answer 1

I would recommend creating a static encoder so you don't create a new encoder every time you call that property:

extension JSONEncoder {
    static let shared = JSONEncoder()
    static let iso8601 = JSONEncoder(dateEncodingStrategy: .iso8601)
    static let iso8601PrettyPrinted = JSONEncoder(dateEncodingStrategy: .iso8601, outputFormatting: .prettyPrinted)
}

---

extension JSONEncoder {    
    convenience init(dateEncodingStrategy: DateEncodingStrategy,
                         outputFormatting: OutputFormatting = [],
                      keyEncodingStrategy: KeyEncodingStrategy = .useDefaultKeys) {
        self.init()
        self.dateEncodingStrategy = dateEncodingStrategy
        self.outputFormatting = outputFormatting
        self.keyEncodingStrategy = keyEncodingStrategy
    }
}

---

Considering that you are calling this method inside a Encodable extension you can just force try!. You can also force the conversion from data to string:

extension Encodable {
    func data(using encoder: JSONEncoder = .iso8601) throws -> Data {
        try encoder.encode(self)
    }
    func dataPrettyPrinted() throws -> Data {
        try JSONEncoder.iso8601PrettyPrinted.encode(self)
    }
    // edit if you need the data using a custom date formatter
    func dataDateFormatted(with dateFormatter: DateFormatter) throws -> Data {
        JSONEncoder.shared.dateEncodingStrategy = .formatted(dateFormatter)
        return try JSONEncoder.shared.encode(self)
    }
    func json() throws -> String {
         String(data: try data(), encoding: .utf8) ?? ""
    }
    func jsonPrettyPrinted() throws -> String {
        String(data: try dataPrettyPrinted(), encoding: .utf8) ?? ""
    }
    func jsonDateFormatted(with dateFormatter: DateFormatter) throws -> String {
        return String(data: try dataDateFormatted(with: dateFormatter), encoding: .utf8) ?? ""
    }
}

---

Playground testing

struct Foo: Codable {
    let string1: String
    let string2: String
    let date: Date
    let val: Int
    let bar: Bar
}
struct Bar: Codable {
    let name: String
}

---

let bar = Bar(name: "Fred")
let foo = Foo(string1: "string1", string2: "string2", date: Date(), val: 42, bar: bar)

try! print("JSON\n=================\n", foo.json(), terminator: "\n\n")
try! print("JSONPrettyPrinted\n=================\n", foo.jsonPrettyPrinted(), terminator: "\n\n")
let dateFormatter = DateFormatter()
dateFormatter.dateStyle = .long
try! print("JSONDateFormatted\n=================\n", foo.jsonDateFormatted(with: dateFormatter))

This will print

JSON
=================
{"date":"2020-11-06T20:22:55Z","bar":{"name":"Fred"},"string1":"string1","val":42,"string2":"string2"}

JSONPrettyPrinted
=================
{
"date" : "2020-11-06T20:22:55Z",
"bar" : {
"name" : "Fred"
},
"string1" : "string1",
"val" : 42,
"string2" : "string2"
}

JSONDateFormatted
=================
{"date":"6 November 2020","bar":{"name":"Fred"},"string1":"string1","val":42,"string2":"string2"}