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 project
Usage
Download
Gradle
//gradle kotlin DSL
implementation("com.github.doyaaaaaken:kotlin-csv-jvm:1.7.0") //for JVM platform
implementation("com.github.doyaaaaaken:kotlin-csv-js:1.7.0") //for Kotlin JS platform
//gradle groovy DSL
implementation 'com.github.doyaaaaaken:kotlin-csv-jvm:1.7.0' //for JVM platform
implementation 'com.github.doyaaaaaken:kotlin-csv-js:1.7.0' //for Kotlin JS platform
Maven
<dependency>
<groupId>com.github.doyaaaaaken</groupId>
<artifactId>kotlin-csv-jvm</artifactId>
<version>1.7.0</version>
</dependency>
<dependency>
<groupId>com.github.doyaaaaaken</groupId>
<artifactId>kotlin-csv-js</artifactId>
<version>1.7.0</version>
</dependency>
@file:DependsOn("com.github.doyaaaaaken:kotlin-csv-jvm:1.7.0") //for JVM platform
@file:DependsOn("com.github.doyaaaaaken:kotlin-csv-js:1.7.0")
//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}]
Sequence
Read as Sequence
type allows to execute lazily.
It starts to process each rows before reading all row data.
See detail about Sequence
type on Kotlin official document.
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()
}
Suspending Function
Read in a 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. |
false |
Deprecated. Replace with appropriate values in excessFieldsRowBehaviour and insufficientFieldsRowBehaviour , e.g. both set to IGNORE . 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). |
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))
}
Suspending Function
Write in a 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\n |
Character used as line terminator. |
outputLastLineTerminator | true |
Output line break at the end 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) |
Links
Documents
Libraries which use kotlin-csv
- kotlin-grass: Csv File to Kotlin Data Class Parser.
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
Copyright © 2019 doyaaaaaken.
This project is licensed under Apache 2.0.
This project is inspired ❤️ by scala-csv
This README was generated with ❤️ by readme-md-generator