Comma-Separated Values - CSV

Comma-Separated Values are used as interchange format for tabular data of text. This format is supported by most spreadsheet applications and may be used as database extraction format.

Despite the name the values are often separated by a semicolon ;.

Even though the format is interpreted differently there exists a formal specification in RFC4180.

The format uses three different characters to structure the data:

Field Delimiter - separates the columns from each other (e.g. , or ;)
Quote - marks columns that may contain other structuring characters (such as Field Delimiters or line break) (e.g. ")
Escape Character - used to escape Field Delimiters in columns (e.g. \)

Lines are separated by either Line Feed (\n = ASCII 10) or Carriage Return and Line Feed (\r = ASCII 13 + \n = ASCII 10).

Project Info: Alpakka CSV
Artifact	com.lightbend.akka akka-stream-alpakka-csv 9.0.0 Snapshots are available
JDK versions	Eclipse Temurin JDK 11 Eclipse Temurin JDK 17
Scala versions	2.13.12, 3.3.3
JPMS module name	akka.stream.alpakka.csv
License	BUSL-1.1
Readiness level	Supported, support is available from Lightbend Since 1.0.0, 2019-04-04
Home page	https://doc.akka.io/libraries/alpakka/current
API documentation	API (Scaladoc)
Forums	Akka Discuss
Release notes	GitHub releases
Issues	Github issues
Sources	https://github.com/akka/alpakka

Artifacts

The Akka dependencies are available from Akka’s library repository. To access them there, you need to configure the URL for this repository.

sbt

resolvers += "Akka library repository".at("https://repo.akka.io/maven")

Maven

<project>
  ...
  <repositories>
    <repository>
      <id>akka-repository</id>
      <name>Akka library repository</name>
      <url>https://repo.akka.io/maven</url>
    </repository>
  </repositories>
</project>

Gradle

repositories {
    mavenCentral()
    maven {
        url "https://repo.akka.io/maven"
    }
}

Additionally, add the dependencies as below.

sbt

val AkkaVersion = "2.10.0"
libraryDependencies ++= Seq(
  "com.lightbend.akka" %% "akka-stream-alpakka-csv" % "9.0.0",
  "com.typesafe.akka" %% "akka-stream" % AkkaVersion
)

Maven

<properties>
  <akka.version>2.10.0</akka.version>
  <scala.binary.version>2.13</scala.binary.version>
</properties>
<dependencies>
  <dependency>
    <groupId>com.lightbend.akka</groupId>
    <artifactId>akka-stream-alpakka-csv_${scala.binary.version}</artifactId>
    <version>9.0.0</version>
  </dependency>
  <dependency>
    <groupId>com.typesafe.akka</groupId>
    <artifactId>akka-stream_${scala.binary.version}</artifactId>
    <version>${akka.version}</version>
  </dependency>
</dependencies>

Gradle

def versions = [
  AkkaVersion: "2.10.0",
  ScalaBinary: "2.13"
]
dependencies {
  implementation "com.lightbend.akka:akka-stream-alpakka-csv_${versions.ScalaBinary}:9.0.0"
  implementation "com.typesafe.akka:akka-stream_${versions.ScalaBinary}:${versions.AkkaVersion}"
}

The table below shows direct dependencies of this module and the second tab shows all libraries it depends on transitively.

Direct dependencies

Organization	Artifact	Version
com.typesafe.akka	akka-stream_2.13	2.10.0
org.scala-lang	scala-library	2.13.12

Dependency tree

com.typesafe.akka    akka-stream_2.13    2.10.0    BUSL-1.1
    com.typesafe.akka    akka-actor_2.13    2.10.0    BUSL-1.1
        com.typesafe    config    1.4.3    Apache-2.0
        org.scala-lang    scala-library    2.13.12    Apache-2.0
    com.typesafe.akka    akka-protobuf-v3_2.13    2.10.0    BUSL-1.1
    org.reactivestreams    reactive-streams    1.0.4    MIT-0
    org.scala-lang    scala-library    2.13.12    Apache-2.0
org.scala-lang    scala-library    2.13.12    Apache-2.0

CSV parsing

CSV parsing offers a flow that takes a stream of akka.util.ByteString and issues a stream of lists of ByteString.

The incoming data must contain line ends to allow line base framing. The CSV special characters can be specified (as bytes), suitable values are available as constants in CsvParsing.

Note

The current parser is limited to byte-based character sets (UTF-8, ISO-8859-1, ASCII) and can’t parse double-byte encodings (e.g. UTF-16).

The parser accepts Byte Order Mark (BOM) for UTF-8, but will fail for UTF-16 and UTF-32 Byte Order Marks.

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.CsvParsing

val flow: Flow[ByteString, List[ByteString], NotUsed]
  = CsvParsing.lineScanner(delimiter, quoteChar, escapeChar)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;

Flow<ByteString, Collection<ByteString>, NotUsed> flow =
    CsvParsing.lineScanner(delimiter, quoteChar, escapeChar);

In this sample we read a single line of CSV formatted data into a list of column elements:

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.CsvParsing

Source.single(ByteString("eins,zwei,drei\n"))
  .via(CsvParsing.lineScanner())
  .runWith(Sink.head)

result should be(List(ByteString("eins"), ByteString("zwei"), ByteString("drei")))

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;

Source.single(ByteString.fromString("eins,zwei,drei\n"))
    .via(CsvParsing.lineScanner())
    .runWith(Sink.head(), system);

To convert the ByteString columns as String, a map operation can be added to the Flow:

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.CsvParsing

Source.single(ByteString("eins,zwei,drei\n"))
  .via(CsvParsing.lineScanner())
  .map(_.map(_.utf8String))
  .runWith(Sink.head)

result should be(List("eins", "zwei", "drei"))

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;

Source.single(ByteString.fromString("eins,zwei,drei\n"))
    .via(CsvParsing.lineScanner())
    .map(line -> line.stream().map(ByteString::utf8String).collect(Collectors.toList()))
    .runWith(Sink.head(), system);

CSV conversion into a map

The column-based nature of CSV files can be used to read it into a map of column names and their ByteString values, or alternatively to String values. The column names can be either provided in code or the first line of data can be interpreted as the column names.

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.CsvToMap

// keep values as ByteString
val flow1: Flow[List[ByteString], Map[String, ByteString], NotUsed]
  = CsvToMap.toMap()

val flow2: Flow[List[ByteString], Map[String, ByteString], NotUsed]
  = CsvToMap.toMap(StandardCharsets.UTF_8)

val flow3: Flow[List[ByteString], Map[String, ByteString], NotUsed]
  = CsvToMap.withHeaders("column1", "column2", "column3")

// values as String (decode ByteString)
val flow4: Flow[List[ByteString], Map[String, String], NotUsed]
= CsvToMap.toMapAsStrings(StandardCharsets.UTF_8)

val flow5: Flow[List[ByteString], Map[String, String], NotUsed]
= CsvToMap.withHeadersAsStrings(StandardCharsets.UTF_8, "column1", "column2", "column3")


// values as String (decode ByteString)
val flow6: Flow[List[ByteString], Map[String, String], NotUsed]
= CsvToMap.toMapAsStringsCombineAll(StandardCharsets.UTF_8, Option.empty)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;
import akka.stream.alpakka.csv.javadsl.CsvToMap;

// keep values as ByteString
Flow<Collection<ByteString>, Map<String, ByteString>, ?> flow1 = CsvToMap.toMap();

Flow<Collection<ByteString>, Map<String, ByteString>, ?> flow2 =
    CsvToMap.toMap(StandardCharsets.UTF_8);

Flow<Collection<ByteString>, Map<String, ByteString>, ?> flow3 =
    CsvToMap.withHeaders("column1", "column2", "column3");

// values as String (decode ByteString)
Flow<Collection<ByteString>, Map<String, String>, ?> flow4 =
    CsvToMap.toMapAsStrings(StandardCharsets.UTF_8);

Flow<Collection<ByteString>, Map<String, String>, ?> flow5 =
    CsvToMap.withHeadersAsStrings(StandardCharsets.UTF_8, "column1", "column2", "column3");

// values as String (decode ByteString)
Flow<Collection<ByteString>, Map<String, String>, ?> flow6 =
    CsvToMap.toMapAsStringsCombineAll(
        StandardCharsets.UTF_8, Optional.empty(), Optional.empty());

This example uses the first line (the header line) in the CSV data as column names:

Scala

source  import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

  // values as ByteString
  Source
    .single(ByteString("""eins,zwei,drei
                         |11,12,13
                         |21,22,23
                         |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMap())
    .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> ByteString("11"), "zwei" -> ByteString("12"), "drei" -> ByteString("13")),
      Map("eins" -> ByteString("21"), "zwei" -> ByteString("22"), "drei" -> ByteString("23"))
    )
  )

  // values as String
  Source
    .single(ByteString("""eins,zwei,drei
                         |11,12,13
                         |21,22,23
                         |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMapAsStrings())
    .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> "11", "zwei" -> "12", "drei" -> "13"),
      Map("eins" -> "21", "zwei" -> "22", "drei" -> "23")
    )
  )
  import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

  // values as ByteString
  Source
    .single(ByteString("""eins,zwei,drei,vier,fünt
                          |11,12,13
                          |21,22,23
                          |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMapAsStringsCombineAll(headerPlaceholder = Option.empty))
    .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> "11", "zwei" -> "12", "drei" -> "13", "vier" -> "", "fünt" -> ""),
      Map("eins" -> "21", "zwei" -> "22", "drei" -> "23", "vier" -> "", "fünt" -> "")
    )
  )
  import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

  // values as ByteString
  Source
    .single(ByteString("""eins,zwei,drei
                          |11,12,13,14
                          |21,22,23
                          |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMapAsStringsCombineAll(headerPlaceholder = Option.empty))
    .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> "11", "zwei" -> "12", "drei" -> "13", "MissingHeader0" -> "14"),
      Map("eins" -> "21", "zwei" -> "22", "drei" -> "23")
    )
  )
  import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

  // values as ByteString
  Source
    .single(ByteString("""eins,zwei
                          |11,12,13
                          |21,22,
                          |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMapAsStringsCombineAll(headerPlaceholder = Option("MyCustomHeader")))
    .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> "11", "zwei" -> "12", "MyCustomHeader0" -> "13"),
      Map("eins" -> "21", "zwei" -> "22", "MyCustomHeader0" -> "")
    )
  )
  import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

    // values as ByteString
    Source
      .single(ByteString("""eins,zwei,drei,fünt
                            |11,12,13
                            |21,22,23
                            |""".stripMargin))
      .via(CsvParsing.lineScanner())
      .via(CsvToMap.toMapAsStringsCombineAll(customFieldValuePlaceholder = Option("missing")))
      .runWith(Sink.seq)

  result should be(
    Seq(
      Map("eins" -> "11", "zwei" -> "12", "drei" -> "13", "fünt" -> "missing"),
      Map("eins" -> "21", "zwei" -> "22", "drei" -> "23", "fünt" -> "missing")
    )
  )
import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

// values as ByteString
Source
  .single(ByteString("""eins,zwei,drei,vier,fünt
                        |11,12,13
                        |21,22,23
                        |""".stripMargin))
  .via(CsvParsing.lineScanner())
  .via(CsvToMap.toMapCombineAll(headerPlaceholder = Option.empty))
  .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> ByteString("11"),
        "zwei" -> ByteString("12"),
        "drei" -> ByteString("13"),
        "vier" -> ByteString(""),
        "fünt" -> ByteString("")),
    Map("eins" -> ByteString("21"),
        "zwei" -> ByteString("22"),
        "drei" -> ByteString("23"),
        "vier" -> ByteString(""),
        "fünt" -> ByteString(""))
  )
)
import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

// values as ByteString
  Source
  .single(ByteString("""eins,zwei,drei
                        |11,12,13,14,15
                        |21,22,23
                        |""".stripMargin))
  .via(CsvParsing.lineScanner())
  .via(CsvToMap.toMapCombineAll(headerPlaceholder = Option.empty))
  .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> ByteString("11"),
        "zwei" -> ByteString("12"),
        "drei" -> ByteString("13"),
        "MissingHeader0" -> ByteString("14"),
        "MissingHeader1" -> ByteString("15")),
    Map("eins" -> ByteString("21"), "zwei" -> ByteString("22"), "drei" -> ByteString("23"))
  )
)
import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

// values as ByteString
  Source
  .single(ByteString("""eins,zwei
                        |11,12,13
                        |21,22,
                        |""".stripMargin))
  .via(CsvParsing.lineScanner())
  .via(CsvToMap.toMapCombineAll(headerPlaceholder = Option("MyCustomHeader")))
  .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> ByteString("11"), "zwei" -> ByteString("12"), "MyCustomHeader0" -> ByteString("13")),
    Map("eins" -> ByteString("21"), "zwei" -> ByteString("22"), "MyCustomHeader0" -> ByteString(""))
  )
)
import akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

  // values as ByteString
  Source
    .single(ByteString("""eins,zwei,drei,fünt
                          |11,12,13
                          |21,22,
                          |""".stripMargin))
    .via(CsvParsing.lineScanner())
    .via(CsvToMap.toMapCombineAll(headerPlaceholder = Option("MyCustomHeader"), customFieldValuePlaceholder = Option(ByteString("missing"))))
    .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> ByteString("11"),
        "zwei" -> ByteString("12"),
        "drei" -> ByteString("13"),
        "fünt" -> ByteString("missing")),
    Map("eins" -> ByteString("21"),
        "zwei" -> ByteString("22"),
        "drei" -> ByteString(""),
        "fünt" -> ByteString("missing"))
  )
)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;
import akka.stream.alpakka.csv.javadsl.CsvToMap;

    // values as ByteString
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(CsvToMap.toMap(StandardCharsets.UTF_8))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("3")));

    // values as String
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(CsvToMap.toMapAsStrings(StandardCharsets.UTF_8))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("3"));
    // values as ByteString
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3,4,5"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.empty()))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("3")));
assertThat(map.get("MissingHeader0"), equalTo(ByteString.fromString("4")));
assertThat(map.get("MissingHeader1"), equalTo(ByteString.fromString("5")));
    // values as ByteString
    Source.single(ByteString.fromString("eins,zwei,drei,vier,fünt\n1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.empty()))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("3")));
assertThat(map.get("vier"), equalTo(ByteString.fromString("")));
assertThat(map.get("fünt"), equalTo(ByteString.fromString("")));
    // values as ByteString
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3,4,5"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.of("MyCustomHeader")))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("3")));
assertThat(map.get("MyCustomHeader0"), equalTo(ByteString.fromString("4")));
assertThat(map.get("MyCustomHeader1"), equalTo(ByteString.fromString("5")));
    // values as ByteString
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapCombineAll(
                StandardCharsets.UTF_8,
                Optional.of(ByteString.fromString("missing")),
                Optional.of("MyCustomHeader")))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("missing")));

This sample will generate the same output as above, but the column names are specified in the code:

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.{CsvParsing, CsvToMap}

// values as ByteString
Source
  .single(ByteString(
    """11,12,13
      |21,22,23
      |""".stripMargin))
  .via(CsvParsing.lineScanner())
  .via(CsvToMap.withHeaders("eins", "zwei", "drei"))
  .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> ByteString("11"), "zwei" -> ByteString("12"), "drei" -> ByteString("13")),
    Map("eins" -> ByteString("21"), "zwei" -> ByteString("22"), "drei" -> ByteString("23"))
  )
)

// values as String
Source
  .single(ByteString("""11,12,13
                       |21,22,23
                       |""".stripMargin))
  .via(CsvParsing.lineScanner())
  .via(CsvToMap.withHeadersAsStrings(StandardCharsets.UTF_8, "eins", "zwei", "drei"))
  .runWith(Sink.seq)

result should be(
  Seq(
    Map("eins" -> "11", "zwei" -> "12", "drei" -> "13"),
    Map("eins" -> "21", "zwei" -> "22", "drei" -> "23")
  )
)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvParsing;
import akka.stream.alpakka.csv.javadsl.CsvToMap;

    // values as ByteString
    Source.single(ByteString.fromString("1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(CsvToMap.withHeaders("eins", "zwei", "drei"))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo(ByteString.fromString("1")));
assertThat(map.get("zwei"), equalTo(ByteString.fromString("2")));
assertThat(map.get("drei"), equalTo(ByteString.fromString("3")));

    // values as String
    Source.single(ByteString.fromString("1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(CsvToMap.withHeadersAsStrings(StandardCharsets.UTF_8, "eins", "zwei", "drei"))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("3"));

    // values as String
    Source.single(ByteString.fromString("eins,zwei,drei,vier,fünt\n1,2,3"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapAsStringsCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.empty()))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("3"));
assertThat(map.get("vier"), equalTo(""));
assertThat(map.get("fünt"), equalTo(""));

    // values as String
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3,4,5"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapAsStringsCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.empty()))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("3"));
assertThat(map.get("MissingHeader0"), equalTo("4"));
assertThat(map.get("MissingHeader1"), equalTo("5"));

    // values as String
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2,3,4,5"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapAsStringsCombineAll(
                StandardCharsets.UTF_8, Optional.empty(), Optional.of("MyCustomHeader")))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("3"));
assertThat(map.get("MyCustomHeader0"), equalTo("4"));
assertThat(map.get("MyCustomHeader1"), equalTo("5"));

    // values as String
    Source.single(ByteString.fromString("eins,zwei,drei\n1,2"))
        .via(CsvParsing.lineScanner())
        .via(
            CsvToMap.toMapAsStringsCombineAll(
                StandardCharsets.UTF_8, Optional.of("missing"), Optional.of("MyCustomHeader")))
        .runWith(Sink.head(), system);

assertThat(map.get("eins"), equalTo("1"));
assertThat(map.get("zwei"), equalTo("2"));
assertThat(map.get("drei"), equalTo("missing"));

CSV formatting

To emit CSV files immutable.Seq[String] can be formatted into ByteString e.g to be written to file. The formatter takes care of quoting and escaping.

Certain CSV readers (e.g. Microsoft Excel) require CSV files to indicate their character encoding with a Byte Order Mark (BOM) in the first bytes of the file. Choose an appropriate Byte Order Mark matching the selected character set from the constants in ByteOrderMark (Unicode FAQ on Byte Order Mark).

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.{CsvFormatting, CsvQuotingStyle}

val flow: Flow[immutable.Seq[String], ByteString, _]
  = CsvFormatting.format(delimiter,
                         quoteChar,
                         escapeChar,
                         endOfLine,
                         CsvQuotingStyle.Required,
                         charset = StandardCharsets.UTF_8,
                         byteOrderMark = None)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvFormatting;
import akka.stream.alpakka.csv.javadsl.CsvQuotingStyle;

Flow<Collection<String>, ByteString, ?> flow1 = CsvFormatting.format();

Flow<Collection<String>, ByteString, ?> flow2 =
    CsvFormatting.format(
        delimiter,
        quoteChar,
        escapeChar,
        endOfLine,
        CsvQuotingStyle.REQUIRED,
        charset,
        byteOrderMark);

This example uses the default configuration:

Delimiter: comma (,)
Quote char: double quote (")
Escape char: backslash (\)
Line ending: Carriage Return and Line Feed (\r = ASCII 13 + \n = ASCII 10)
Quoting style: quote only if required
Charset: UTF-8
No Byte Order Mark

Scala

sourceimport akka.stream.alpakka.csv.scaladsl.CsvFormatting

Source
  .single(List("eins", "zwei", "drei"))
  .via(CsvFormatting.format())
  .runWith(Sink.head)

Java

sourceimport akka.stream.alpakka.csv.javadsl.CsvFormatting;
import akka.stream.alpakka.csv.javadsl.CsvQuotingStyle;

Source.single(Arrays.asList("one", "two", "three"))
    .via(CsvFormatting.format())
    .runWith(Sink.head(), system);