Expression Language
Use the Gatling Expression Language to generate dynamic parameters
Most Gatling DSL methods can be passed Gatling Expression Language (EL) Strings.
This is a very convenient feature to pass dynamic parameters.
Only Gatling DSL methods will interpolate Gatling EL Strings. You can’t use Gatling EL in your own methods or functions.
For example queryParam("latitude", session -> "#{latitude}") wouldn’t work because the parameter is not a String, but a function that returns a String.
Also, queryParam("latitude", Integer.parseInt("#{latitude}")) wouldn’t work either because Integer.parseInt would be called on the "#{latitude}" String before trying to pass the result to the queryParam method.
The solution here would be to pass a function:
queryParam("latitude", session -> session.getInt("latitude")).
Syntax
Gatling EL uses a #{attributeName} syntax to define placeholders to be replaced with the value of the matching attributeName attribute’s value stored in the virtual user’s Session, eg: request("page").get("/foo?param=#{bar}").
// direct attribute access
"#{foo}"
// access by index
// supports arrays, Java List, Scala Seq and Product
// n can be negative to count backward from the end
"#{foo(n)}"
// access by key
// supports Java Map, Java POJO, Java records, Scala Map and Scala case class
"#{foo.bar}"
The previous ${} syntax is deprecated because it was clashing with Scala and Kotlin String interpolation. It will be dropped in a future release.
Please make sure to use the #{} syntax from now on.
Built-in Functions
Gatling EL provide the following built-in functions:
// collection size
// supports arrays, Java List, Scala Seq and Product
"#{foo.size()}"
// collection size
// supports arrays, Java Collection, Java Map, Scala Iterable and Product
// collection random element
// supports arrays, Java Collection, Java List, Scala Seq and Product
"#{foo.random()}"
// true if the session contains a `foo` attribute
"#{foo.exists()}"
// true if the session doesn't contains a `foo` attribute
"#{foo.isUndefined()}"
// properly formats into a JSON value (wrap Strings with double quotes, deal with null)
"#{foo.jsonStringify()}"
// System.currentTimeMillis
"#{currentTimeMillis()}"
// ZonedDateTime.now() formatted with a java.time.format.DateTimeFormatter pattern
"#{currentDate(<pattern>)}"
// unescape an HTML String (entities decoded)
"#{foo.htmlUnescape()}"
You can combine different Gatling EL builtin functions, eg:
// return first element of the first list in `foo`
"#{foo(0)(0)}"
// return a random element from the List associated with key `list` in the Map `foo`
"#{foo.list.random()}"
Escaping
To prevent "#{" from being interpreted by the EL compiler, add a \\ before it. "\\#{foo}" will be turned into "#{foo}".
If you want a $ before the placeholder, add another $.
Assuming the session attribute foo holds "FOO", "$$${foo}" will be turned into "$FOO".
This can go on and on. In general, if there are 2n-1 $ characters before ${ – an even number of $ characters totally –
there will be n $ before { in the final string;
if there are 2n $ before ${ – an odd number totally – there will be n $ before the placeholder.