Jmeter generate json payload of request dynamically

Question

I have a Jmeter test plan where I want my HttpSampler to send a post request.

The body of the request should contain Json as follows:

{
  "productIds" : [
    "p1",
    "p2",
    ...
  ]
}

I have setup a random variable generator that returns well-formed productId with every call. What I would like to do is generating the payload by filling productIds of random pid's taken from the generator, directly in the body of the request. Something like (suppose *** is the scripting escape):

{
  "productIds" : [
     ***
       for i in (1, $productsCount) {
         write("\"$randomPid\"\n")
       }
     ***
  ]
}

Is it possible? If yes, how? If not, how would you approach the issue?

Thanks!

Solution

1. Add a Beanshell PreProcessor as a child of the request you want to parametrize

2. Put following code into the PreProcessor's "Script" area:

   StringBuilder result = new StringBuilder();
   String newline = System.getProperty("line.separator");
   int max = Integer.parseInt(Parameters);
   Random random = new Random();
   
   result.append("{");
   result.append("\"productIds\" : [");
   result.append(newline);
   for (int i = 1; i < max; i++) {
       result.append("\"").append(random.nextInt()).append("\",");
       result.append(newline);
   }
   result.append("]");
   result.append(newline);
   result.append("}");
   
   vars.put("json", result.toString());
   

3. Put your ${productsCount} value into "Parameters" stanza
4. Refer generated payload as ${json} where required

See How to use BeanShell: JMeter's favorite built-in component guide for more details on Beanshell scripting in Apache JMeter.

Comments

[Diego Martinoia]

Yeah, that's the way I did it before seeing your answer, was wondering if it was possible to do within the http request payload directly, but this is also ok. Thanks!

[Dmitri T]

You can use __Beanshell function right in the request body but the whole approach from coding perspective will be the same