Java 8 dates and times

Java 8 comes with a better thought out dates and times API. Unfortunately, it cannot be supported as part of the core kantan.csv API - we still support Java 7. There is, however, a dedicated optional module that you can include by adding the following line to your build.sbt file:

libraryDependencies += "com.nrinaudo" %% "kantan.csv-java8" % "0.7.0"

You then need to import the corresponding package:

import kantan.csv.java8._

kantan.csv has default, ISO 8601 compliant CellDecoder and CellEncoder instances for the following types:

Let’s imagine for example that we want to extract dates from the following string:

import java.time._
import kantan.csv._
import kantan.csv.ops._

val plainInput = "1,1978-12-10\n2,2015-01-09"

This is directly supported:

val res = plainInput.unsafeReadCsv[List, (Int, LocalDate)](rfc)
// res: List[(Int, LocalDate)] = List((1, 1978-12-10), (2, 2015-01-09))

res.asCsv(rfc)
// res0: String = """1,1978-12-10
// 2,2015-01-09
// """

It’s also possible to declare your own CellDecoder and CellEncoder instances. Let’s take, for example, the following custom format:

import java.time.format.DateTimeFormatter
import java.time._
import kantan.csv._
import kantan.csv.java8._
import kantan.csv.ops._

val input = "1,10-12-1978\n2,09-01-2015"

val format = DateTimeFormatter.ofPattern("dd-MM-yyyy")

We then need to build a decoder for it and stick it in the implicit scope:

implicit val decoder: CellDecoder[LocalDate] = localDateDecoder(format)

And we’re done:

val result = input.unsafeReadCsv[List, (Int, LocalDate)](rfc)
// result: List[(Int, LocalDate)] = List((1, 1978-12-10), (2, 2015-01-09))

Similarly, this is how you create and encoder:

implicit val encoder: CellEncoder[LocalDate] = localDateEncoder(format)

And you can now easily encode data that contains instances of LocalDate:

result.asCsv(rfc)
// res2: String = """1,10-12-1978
// 2,09-01-2015
// """

Note that if you’re going to both encode and decode dates, you can create a CellCodec in a single call instead:

val codec: CellCodec[LocalDate] = localDateCodec(format)

Note that while you can pass a DateTimeFormatter directly, the preferred way of dealing with pattern strings is to use the literal syntax provided by kantan.csv:

localDateDecoder(fmt"dd-MM-yyyy")

The advantage is that this is checked at compile time - invalid pattern strings will cause a compilation error:

localDateDecoder(fmt"FOOBAR")
// error: Illegal format: 'FOOBAR'
// localDateDecoder(fmt"FOOBAR")
//                  ^^^^^^^^^^^
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