Create a Gatling feeder file using REST calls

gatlingGeneratedFeeder.scala

/*
Basic blocks of code that will build a CSV file using repsonse data from API calls

This is a "one-off" process, meaning you will 
1. run Gatling script to generate CSV file using REST calls (usually POSTS, but GETS or datbase queries could work ) 
2. copy the file into your project
3. compile and run Gatling 
*/

class MySimulation extends Simulation {
  // output file
  val nameOfMyFile = "coolFeeder.csv"
  val filePath = "fully/qualified/path/to/file/"
  
  /* file writer object */
  val myFileWriter = {
    val output = new FileOutputStream( filePath)
    val pw = new java.io.PrintWriter( output, true)
    //print header row for the file (just once)
    pw.println("My,File,Column,Headers,Go,Here")
    pw
  }
  
  /* function that extracts values from Gatling session (a huge Map) and forms them into a csv row (all Strings of course)
  // format: rowvalue1, rowvalue2, rowvalue3, etc */
  dev buildRow( session:Session): String = {
    val filtered = new StringBuilder
    filtered ++= session.get("Attribute1").as[String].concat(",")
    filtered ++= session.get("Attribute2").as[String].concat(",")
    // ...add as many of these as you need to create a complete row 
    val result = filtered.toString()
    result   
  }
  
  /* Gatling scenario that produces data for your file
       The key thing that makes it work is being able to access and manipulate Gatling Session attributes. 
  */
  val scnPost = scenario("My-Uniquely-Named-Scenario")
    .exec( session => {
      session.set("Attribute1", valueForAttribute1.toString()).set("Attribute2", valueForAttribute2.toString())
      // ...repeat this pattern until all your attributes are saved from the request 
      // There should be at least one attribute for each column in your final file
      
      // build your request payload, headers, and exec the scenario ( code not included)
      .exec( yourcodeThatGetsOrCreatesData )
      
      // call "exec" a SECOND  time to transfer data from the session object to buildRow()
      .exec( session  => {
          val dataRow = buildRow( session )
          println("***Debug: row sent to file = " + dataRow)
          val writer = myFileWriter
          writer.println( dataRow )
          session
      })
      
      before {
        println("*** creating feeder file ***")
      }
      
      setUp(
        scenario.inject( loadprofile)).protocols( standardHttp)
      )
      
      
      after {
        println("Done")
      }   
  
}

It was very much useful :)
Thank you.

You are very welcome!

Yeap, very useful, cheers.

Thank you!
!But resource leaks)
you must close, at the end of simulation:

 val output = new FileOutputStream( filePath)
 val pw = new java.io.PrintWriter( output, true)