Jmeter - How to fetch IDs from a json response and use it in the next request

Question

From a JSON response of the format below,

{"data":[{"id":"xxx","data":{"A":"111","B":"222","C":"333"}},{"id":"yyy","data":{"A":"111","B":"222","C":"333"}}]

I need to fetch only IDs and pass it in the next request as a list like

{"data":["xxx","yyy"]}

I was able to fetch all these IDs using a Regular Expression Extractor with the following values.

Reference Name = data ; 
Regex = "id":"(.+?)" ;
Template = $1$ ;
Match No = -1 ;

The IDs retrieved are in the following format.

data_1 = xxx
data_2 = yyy

But the IDs could be a lot, so I need an efficient way where I can use just one variable instead of using {"data":["data_1","data_2"]} and so on.

Answer 1

You can build a single variable out of these data_1, data_2, etc. as follows:

1. Add Beanshell PostProcessor after your Regular Expression Extractor

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

   StringBuilder dataBuilder = new StringBuilder();
   dataBuilder.append("{\"data\":[");
   
   int ids = Integer.parseInt(vars.get("data_matchNr"));
   for (int i = 1; i <= ids; i++) {
   
       dataBuilder.append("\"").append(vars.get("data_" + i)).append("\"");
       if (i < ids) {
           dataBuilder.append(",");
       }
   
   }
   
   dataBuilder.append("]}");
   
   vars.put("data", dataBuilder.toString());
   

Above code will concatenate all the variables prefixed with data_ coming from the Regular Expression Extractor into a single JSON array. You can refer the resulting value as ${data} where required.

References:

• StringBuilder
• JMeterVariables
• How to Use BeanShell: JMeter's Favorite Built-in Component