Scala create multi-line JSON String

Update 2023: I don't know why anyone would bother generating JSON manually in 2023. Just use some appropriate library that knows how to serialize stuff to JSON.

(original answer)

I assume that your question has nothing to do with JSON, and that you're simply asking how to create very wide strings without violating the horizontal 80-character limit in your Scala code. Fortunately, Scala's string literals have at least the following properties:

• You can go from ordinary code to string-literal mode using quotes "..." and triple quotes """...""".
• You can go from string-literal mode to ordinary code mode using ${...}
• Free monoid over characters is reified as methods, that is, there is the + operation that concatenates string literals.
• The whole construction can be made robust to whitespace and indentation using | and stripMargin.

All together, it allows you to write down arbitrary string literals without ever violating horizontal character limits, in a way that is robust w.r.t. indentation.

In this particular case, you want to make a line break in the ambient scala code without introducing a line break in your text. For this, you simply

• exit the string-literal mode by closing """
• insert concatenation operator + in code mode
• make a line-break
• indent however you want
• re-enter the string-literal mode again by opening """

That is,

"""blah-""" +
"""blah"""

will create the string "blah-blah", without line break in the produced string.

Applied to your concrete problem:

val errorReport: String = (
    """{
      |  "errorName": "blah",
      |  "moreError": "blah2",
      |  "errorMessage": {
      |    "status": "bad",
      |    "message": "Unrecognized token 'noformatting'""" +
    """: was expecting 'null', 'true', 'false' or NaN at """ +
    """[Source: (ByteArrayInputStream); line: 1, column: 25]"
      |  }
      |}
      """
  ).stripMargin

Maybe a more readable option would be to construct the lengthy message separately from the neatly indented JSON, and then use string interpolation to combine the two components:

val errorReport: String = {
  val msg = 
    """Unrecognized token 'noformatting': """ +
    """was expecting 'null', 'true', 'false' or NaN at """ +
    """[Source: (ByteArrayInputStream); line: 1, column: 25]"""

    s"""{
      |  "errorName": "blah",
      |  "moreError": "blah2",
      |  "errorMessage": {
      |    "status": "bad",
      |    "message": "${msg}"
      |  }
      |}
      """
  }.stripMargin

If the message itself contains line breaks

Since JSON does not allow multiline string literals, you have to do something else:

• To remove line breaks, use .replaceAll("\\n", "") or rather .replaceAll("\\n", " ")
• To encode line breaks with the escape sequence \n, use .replaceAll("\\n", "\\\\n") (yes... backslashes...)