README

kotlin-csv

Pure Kotlin CSV Reader/Writer.

Design goals

1. Simple interface

easy to setup
use DSL so easy to read

2. Automatic handling of I/O

in Java, we always need to close file. but it's boilerplate code and not friendly for non-JVM user.
provide interfaces which automatically close file without being aware.

3. Multiplatform

Kotlin Multiplatform projects support.

Usage

Download

Gradle

// Gradle Kotlin DSL
implementation("com.github.doyaaaaaken:kotlin-csv-jvm:1.9.3") // for JVM platform
implementation("com.github.doyaaaaaken:kotlin-csv-js:1.9.3") // for Kotlin JS platform

// Gradle Groovy DSL
implementation 'com.github.doyaaaaaken:kotlin-csv-jvm:1.9.3' // for JVM platform
implementation 'com.github.doyaaaaaken:kotlin-csv-js:1.9.3' // for Kotlin JS platform

Maven

<dependency>
  <groupId>com.github.doyaaaaaken</groupId>
  <artifactId>kotlin-csv-jvm</artifactId>
  <version>1.9.3</version>
</dependency>
<dependency>
  <groupId>com.github.doyaaaaaken</groupId>
  <artifactId>kotlin-csv-js</artifactId>
  <version>1.9.3</version>
</dependency>

kscript

@file:DependsOn("com.github.doyaaaaaken:kotlin-csv-jvm:1.9.3") // for JVM platform
@file:DependsOn("com.github.doyaaaaaken:kotlin-csv-js:1.9.3") // for Kotlin JS platform

Examples

CSV Read examples

Simple case

You can read csv file from String, java.io.File or java.io.InputStream object. No need to do any I/O handling. (No need to call use, close and flush method.)

// read from `String`
val csvData: String = "a,b,c\nd,e,f"
val rows: List<List<String>> = csvReader().readAll(csvData)

// read from `java.io.File`
val file: File = File("test.csv")
val rows: List<List<String>> = csvReader().readAll(file)

Read with header

val csvData: String = "a,b,c\nd,e,f"
val rows: List<Map<String, String>> = csvReader().readAllWithHeader(csvData)
println(rows) //[{a=d, b=e, c=f}]

Read as Sequence

Sequence type allows to execute lazily. It starts to process each rows before reading all row data.

Learn more about the Sequence type on Kotlin's official documentation.

csvReader().open("test1.csv") {
    readAllAsSequence().forEach { row: List<String> ->
        //Do something
        println(row) //[a, b, c]
    }
}

csvReader().open("test2.csv") {
    readAllWithHeaderAsSequence().forEach { row: Map<String, String> ->
        //Do something
        println(row) //{id=1, name=doyaaaaaken}
    }
}

NOTE: readAllAsSequence and readAllWithHeaderAsSequence methods can only be called within the open lambda block. The input stream is closed after the open lambda block.

Read line by line

If you want to handle line-by-line, you can do it by using open method. Use open method and then use readNext method inside nested block to read row.

csvReader().open("test.csv") {
    readNext()
}

Read in a Suspending Function

csvReader().openAsync("test.csv") {
    val container = mutalbeListOf<List<String>>()
    delay(100) //other suspending task
    readAllAsSequence().asFlow().collect { row ->
        delay(100) // other suspending task
        container.add(row)
    }
}

Note: openAsync can be and only be accessed through a coroutine or another suspending function

Customize

When you create CsvReader, you can choose read options:

// this is tsv reader's option
val tsvReader = csvReader {
    charset = "ISO_8859_1"
    quoteChar = '"'
    delimiter = '\t'
    escapeChar = '\\'
}

Option

default value

description

logger

no-op

Logger instance for logging debug information at runtime.

charset

UTF-8

Charset encoding. The value must be supported by java.nio.charset.Charset.

quoteChar

"

Character used to quote fields.

delimiter

,

Character used as delimiter between each field. Use "\t" if reading TSV file.

escapeChar

"

Character to escape quote inside field string. Normally, you don't have to change this option. See detail comment on ICsvReaderContext.

skipEmptyLine

false

Whether to skip or error out on empty lines.

autoRenameDuplicateHeaders

false

Whether to auto rename duplicate headers or throw an exception.

~~skipMissMatchedRow~~

false

Deprecated. Replace with appropriate values in excessFieldsRowBehaviour and insufficientFieldsRowBehaviour, e.g. both set to IGNORE. ~~Whether to skip an invalid row. If~~ ignoreExcessCols ~~is true, only rows with less than the expected number of columns will be skipped.~~

excessFieldsRowBehaviour

ERROR

Behaviour to use when a row has more fields (columns) than expected. ERROR (default), IGNORE (skip the row) or TRIM (remove the excess fields at the end of the row to match the expected number of fields).

insufficientFieldsRowBehaviour

ERROR

Behaviour to use when a row has fewer fields (columns) than expected. ERROR (default), IGNORE (skip the row) or EMPTY_STRING (replace missing fields with an empty string).

CSV Write examples

Simple case

You can start writing csv in one line, no need to do any I/O handling (No need to call use, close and flush method.):

val rows = listOf(listOf("a", "b", "c"), listOf("d", "e", "f"))
csvWriter().writeAll(rows, "test.csv")

// if you'd append data on the tail of the file, assign `append = true`.
csvWriter().writeAll(rows, "test.csv", append = true)

// You can also write into OutpusStream.
csvWriter().writeAll(rows, File("test.csv").outputStream())

You can also write a csv file line by line by open method:

val row1 = listOf("a", "b", "c")
val row2 = listOf("d", "e", "f")

csvWriter().open("test.csv") {
    writeRow(row1)
    writeRow(row2)
    writeRow("g", "h", "i")
    writeRows(listOf(row1, row2))
}

Write in a Suspending Function

val rows = listOf(listOf("a", "b", "c"), listOf("d", "e", "f")).asSequence()
csvWriter().openAsync(testFileName) {
    delay(100) //other suspending task
    rows.asFlow().collect {
        delay(100) // other suspending task
        writeRow(it)
    }
}

Write as String

val rows = listOf(listOf("a", "b", "c"), listOf("d", "e", "f"))
val csvString: String = csvWriter().writeAllAsString(rows) //a,b,c\r\nd,e,f\r\n

long-running write (manual control for file close)

If you want to close a file writer manually for performance reasons (e.g. streaming scenario), you can use openAndGetRawWriter and get a raw CsvFileWriter. DO NOT forget to close the writer!

val row1 = listOf("a", "b", "c")

@OptIn(KotlinCsvExperimental::class)
val writer = csvWriter().openAndGetRawWriter("test.csv")
writer.writeRow(row1)
writer.close()

Customize

When you create a CsvWriter, you can choose write options.

val writer = csvWriter {
    charset = "ISO_8859_1"
    delimiter = '\t'
    nullCode = "NULL"
    lineTerminator = "\n"
    outputLastLineTerminator = true
    quote {
        mode = WriteQuoteMode.ALL
        char = '\''
    }
}

Option

default value

description

charset

UTF-8

Charset encoding. The value must be supported by java.nio.charset.Charset.

delimiter

,

Character used as delimiter between each fields. Use "\t" if reading TSV file.

nullCode

(empty string)

Character used when a written field is null value.

lineTerminator

\r

Character used as line terminator.

outputLastLineTerminator

true

Output line break at the end of file or not.

prependBOM

false

Output BOM (Byte Order Mark) at the beginning of file or not.

quote.char

"

Character to quote each fields.

quote.mode

CANONICAL

Quote mode. - CANONICAL: Not quote normally, but quote special characters (quoteChar, delimiter, line feed). This is the specification of CSV. - ALL: Quote all fields. - NON_NUMERIC: Quote non-numeric fields. (ex. 1,"a",2.3)

Miscellaneous

🤝 Contributing

Contributions, issues and feature requests are welcome! If you have questions, ask away in Kotlin Slack's kotlin-csv room.

💻 Development

git clone git@github.com:doyaaaaaken/kotlin-csv.git
cd kotlin-csv
./gradlew check

Show your support

Give a ⭐️ if this project helped you!

📝 License

This project is inspired ❤️ by scala-csv

This README was generated with ❤️ by readme-md-generator

Acknowledgments

This project was originally created by @doyaaaaaken. The initial work and contributions are greatly appreciated.

Next.github

Last updated 10 months ago

Was this helpful?

kotlin-csv

Design goals

1. Simple interface

2. Automatic handling of I/O

3. Multiplatform

Usage

Download

Gradle

Maven

kscript

Examples

CSV Read examples

CSV Write examples

Links

Miscellaneous

🤝 Contributing

💻 Development

Show your support

📝 License

Acknowledgments