Swift 的 JSONDecoder 在 JSON 字符串中有多种日期格式？

Question

Swift 的JSONDecoder 提供了一个dateDecodingStrategy 属性，它允许我们定义如何根据DateFormatter 对象来解释传入的日期字符串。

但是，我目前正在使用一个返回日期字符串 (yyyy-MM-dd) 和日期时间字符串 (yyyy-MM-dd HH:mm:ss) 的 API，具体取决于属性。有没有办法让JSONDecoder 处理这个问题，因为提供的DateFormatter 对象一次只能处理一个dateFormat？

一个笨拙的解决方案是重写随附的Decodable 模型以仅接受字符串作为它们的属性并提供公共Date getter/setter 变量，但这对我来说似乎是一个糟糕的解决方案。有什么想法吗？

Answer 1

向KeyedDecodingContainer

添加扩展

extension KeyedDecodingContainer {
func decodeDate(forKey key: KeyedDecodingContainer<K>.Key, withPossible formats: [DateFormatter]) throws -> Date? {
    
    for format in formats {
        if let date = format.date(from: try self.decode(String.self, forKey: key)) {
            return date
        }
    }
    throw DecodingError.dataCorruptedError(forKey: key, in: self, debugDescription: "Date string does not match format expected by formatter.")
}

}

并使用 'try container.decodeDate(forKey: 'key', withPossible: [.iso8601Full, .yyyyMMdd])'

完整的解决方案在这里：

    import Foundation

extension DateFormatter {
    static let iso8601Full: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        return formatter
    }()
    
    static let yyyyMMdd: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        formatter.calendar = Calendar(identifier: .iso8601)
        formatter.timeZone = TimeZone(secondsFromGMT: 0)
        formatter.locale = Locale(identifier: "en_US_POSIX")
        return formatter
    }()
}

public struct RSSFeed: Codable {
        public let releaseDate: Date?
        public let releaseDateAndTime: Date?
}

extension RSSFeed {
    public init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)

        releaseDate = try container.decodeDate(forKey: .releaseDate, withPossible: [.iso8601Full, .yyyyMMdd])
        releaseDateAndTime = try container.decodeDate(forKey: .releaseDateAndTime, withPossible: [.iso8601Full, .yyyyMMdd])
    }
}

extension KeyedDecodingContainer {
    func decodeDate(forKey key: KeyedDecodingContainer<K>.Key, withPossible formats: [DateFormatter]) throws -> Date? {
        
        for format in formats {
            if let date = format.date(from: try self.decode(String.self, forKey: key)) {
                return date
            }
        }
        throw DecodingError.dataCorruptedError(forKey: key, in: self, debugDescription: "Date string does not match format expected by formatter.")
    }
}

let json = """
{
"releaseDate":"2017-11-12",
"releaseDateAndTime":"2017-11-16 02:02:55"
}
"""

let data = Data(json.utf8)
let decoder = JSONDecoder()
decoder.dateDecodingStrategy = .formatted(DateFormatter.iso8601Full)
let rssFeed = try! decoder.decode(RSSFeed.self, from: data)

let feed = rssFeed
print(feed.releaseDate, feed.releaseDateAndTime)

Answer 2

斯威夫特 5

实际上基于@BrownsooHan 版本使用JSONDecoder 扩展

JSONDecoder+dateDecodingStrategyFormatters.swift

extension JSONDecoder {

    /// Assign multiple DateFormatter to dateDecodingStrategy
    ///
    /// Usage :
    ///
    ///      decoder.dateDecodingStrategyFormatters = [ DateFormatter.standard, DateFormatter.yearMonthDay ]
    ///
    /// The decoder will now be able to decode two DateFormat, the 'standard' one and the 'yearMonthDay'
    ///
    /// Throws a 'DecodingError.dataCorruptedError' if an unsupported date format is found while parsing the document
    var dateDecodingStrategyFormatters: [DateFormatter]? {
        @available(*, unavailable, message: "This variable is meant to be set only")
        get { return nil }
        set {
            guard let formatters = newValue else { return }
            self.dateDecodingStrategy = .custom { decoder in

                let container = try decoder.singleValueContainer()
                let dateString = try container.decode(String.self)

                for formatter in formatters {
                    if let date = formatter.date(from: dateString) {
                        return date
                    }
                }

                throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(dateString)")
            }
        }
    }
}

添加一个只能设置的变量有点笨拙，但您可以轻松地将var dateDecodingStrategyFormatters 转换为func setDateDecodingStrategyFormatters(_ formatters: [DateFormatter]? )

用法

假设您已经在代码中定义了多个DateFormatters，如下所示：

extension DateFormatter {
    static let standardT: DateFormatter = {
        var dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss"
        return dateFormatter
    }()

    static let standard: DateFormatter = {
        var dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
        return dateFormatter
    }()

    static let yearMonthDay: DateFormatter = {
        var dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd"
        return dateFormatter
    }()
}

您现在可以通过设置dateDecodingStrategyFormatters 直接将这些分配给解码器：

// Data structure
struct Dates: Codable {
    var date1: Date
    var date2: Date
    var date3: Date
}

// The Json to decode 
let jsonData = """
{
    "date1": "2019-05-30 15:18:00",
    "date2": "2019-05-30T05:18:00",
    "date3": "2019-04-17"
}
""".data(using: .utf8)!

// Assigning mutliple DateFormatters
let decoder = JSONDecoder()
decoder.dateDecodingStrategyFormatters = [ DateFormatter.standardT,
                                           DateFormatter.standard,
                                           DateFormatter.yearMonthDay ]


do {
    let dates = try decoder.decode(Dates.self, from: jsonData)
    print(dates)
} catch let err as DecodingError {
    print(err.localizedDescription)
}

旁注

我再次意识到将dateDecodingStrategyFormatters 设置为var 有点笨拙，我不推荐它，您应该定义一个函数。但是，这样做是个人喜好。

Answer 3

试试这个。 (斯威夫特 4)

let formatter = DateFormatter()

var decoder: JSONDecoder {
    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .custom { decoder in
        let container = try decoder.singleValueContainer()
        let dateString = try container.decode(String.self)

        formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
        if let date = formatter.date(from: dateString) {
            return date
        }
        formatter.dateFormat = "yyyy-MM-dd"
        if let date = formatter.date(from: dateString) {
            return date
        }
        throw DecodingError.dataCorruptedError(in: container,
            debugDescription: "Cannot decode date string \(dateString)")
    }
    return decoder
}

Answer 4

它有点冗长，但更灵活：用另一个 Date 类包装日期，并为其实现自定义序列化方法。例如：

let dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd"

class MyCustomDate: Codable {
    var date: Date

    required init?(_ date: Date?) {
        if let date = date {
            self.date = date
        } else {
            return nil
        }
    }

    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        let string = dateFormatter.string(from: date)
        try container.encode(string)
    }

    required public init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        let raw = try container.decode(String.self)
        if let date = dateFormatter.date(from: raw) {
            self.date = date
        } else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot parse date")
        }
    }
}

所以现在您独立于 .dateDecodingStrategy 和 .dateEncodingStrategy 并且您的 MyCustomDate 日期将以指定的格式解析。在课堂上使用它：

class User: Codable {
    var dob: MyCustomDate
}

实例化

user.dob = MyCustomDate(date)

Answer 5

如果您在单个模型中有多个不同格式的日期，则为每个日期应用.dateDecodingStrategy 有点困难。

点击此处https://gist.github.com/romanroibu/089ec641757604bf78a390654c437cb0 获取方便的解决方案

Answer 6

面对同样的问题，我写了以下扩展：

extension JSONDecoder.DateDecodingStrategy {
    static func custom(_ formatterForKey: @escaping (CodingKey) throws -> DateFormatter?) -> JSONDecoder.DateDecodingStrategy {
        return .custom({ (decoder) -> Date in
            guard let codingKey = decoder.codingPath.last else {
                throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "No Coding Path Found"))
            }

            guard let container = try? decoder.singleValueContainer(),
                let text = try? container.decode(String.self) else {
                    throw DecodingError.dataCorrupted(DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Could not decode date text"))
            }

            guard let dateFormatter = try formatterForKey(codingKey) else {
                throw DecodingError.dataCorruptedError(in: container, debugDescription: "No date formatter for date text")
            }

            if let date = dateFormatter.date(from: text) {
                return date
            } else {
                throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(text)")
            }
        })
    }
}

此扩展允许您为 JSONDecoder 创建一个 DateDecodingStrategy，以处理同一 JSON 字符串中的多种不同日期格式。该扩展包含一个函数，该函数需要实现一个为您提供 CodingKey 的闭包，您可以为所提供的密钥提供正确的 DateFormatter。

假设您有以下 JSON：

{
    "publication_date": "2017-11-02",
    "opening_date": "2017-11-03",
    "date_updated": "2017-11-08 17:45:14"
}

以下结构：

struct ResponseDate: Codable {
    var publicationDate: Date
    var openingDate: Date?
    var dateUpdated: Date

    enum CodingKeys: String, CodingKey {
        case publicationDate = "publication_date"
        case openingDate = "opening_date"
        case dateUpdated = "date_updated"
    }
}

然后要解码 JSON，您将使用以下代码：

let dateFormatterWithTime: DateFormatter = {
    let formatter = DateFormatter()

    formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"

    return formatter
}()

let dateFormatterWithoutTime: DateFormatter = {
    let formatter = DateFormatter()

    formatter.dateFormat = "yyyy-MM-dd"

    return formatter
}()

let decoder = JSONDecoder()

decoder.dateDecodingStrategy = .custom({ (key) -> DateFormatter? in
    switch key {
    case ResponseDate.CodingKeys.publicationDate, ResponseDate.CodingKeys.openingDate:
        return dateFormatterWithoutTime
    default:
        return dateFormatterWithTime
    }
})

let results = try? decoder.decode(ResponseDate.self, from: data)

Answer 7

请尝试配置与此类似的解码器：

lazy var decoder: JSONDecoder = {
    let decoder = JSONDecoder()
    decoder.dateDecodingStrategy = .custom({ (decoder) -> Date in
        let container = try decoder.singleValueContainer()
        let dateStr = try container.decode(String.self)
        // possible date strings: "2016-05-01",  "2016-07-04T17:37:21.119229Z", "2018-05-20T15:00:00Z"
        let len = dateStr.count
        var date: Date? = nil
        if len == 10 {
            date = dateNoTimeFormatter.date(from: dateStr)
        } else if len == 20 {
            date = isoDateFormatter.date(from: dateStr)
        } else {
            date = self.serverFullDateFormatter.date(from: dateStr)
        }
        guard let date_ = date else {
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Cannot decode date string \(dateStr)")
        }
        print("DATE DECODER \(dateStr) to \(date_)")
        return date_
    })
    return decoder
}()

Answer 8

有几种方法可以解决这个问题：

• 您可以创建一个DateFormatter 子类，它首先尝试日期时间字符串格式，如果失败，则尝试纯日期格式
• 您可以提供.custom Date 解码策略，其中您向Decoder 询问singleValueContainer()，解码一个字符串，并在传递解析日期之前将其传递给您想要的任何格式化程序
• 您可以围绕Date 类型创建一个包装器，它提供了一个自定义的init(from:) 和encode(to:) 来执行此操作（但这并不比.custom 策略更好）
• 您可以按照您的建议使用纯字符串
• 您可以为使用这些日期的所有类型提供自定义init(from:)，并在其中尝试不同的事情

总而言之，前两种方法可能是最简单和最干净的——您将在不牺牲类型安全的情况下在任何地方保留Codable 的默认综合实现。

Answer 9

使用单个编码器无法做到这一点。最好的办法是自定义 encode(to encoder:) 和 init(from decoder:) 方法，并为其中一个值提供您自己的翻译，而为另一个值保留内置的日期策略。

为此考虑将一个或多个格式化程序传递给userInfo 对象可能是值得的。