How to calculate elapsed time between two HTTP samplers in JMeter - jmeter

Question

I tried to calculate elapsed time as follows. I added the code in Beanshell Post Processor something like this (with courtesy of another thread in StackOverflow).
For the sampler1
long request1 = prev.getTime();
vars.put("sampler1", String.valueOf(request1));
And in sampler 2 I added .
long request2 = prev.getTime();
vars.put("sampler2", String.valueOf(request2));
long request1 = Long.parseLong(vars.get("sampler1"));
long request2 = Long.parseLong(vars.get("sampler2"));
long delta = (request1 - request2); // calculate difference
log.info("Time difference is: " + delta + " ms");
And the same delta is captured in .csv file as follows.
FileOutputStream out = new FileOutputStream("delta.csv", true);
out.write((String.valueOf(delta)).getBytes("UTF-8"));
out.write(System.getProperty("line.separator").getBytes("UTF-8"));
out.flush();
out.close();
I do get the values in the CSV file in a single row.
But I'm looking for a way to capture these values using sample variables and map it to other sample variables that I'm capturing in another CSV file.
I appreciate if someone can provide a way to do this.

Answer 1

Instead of writing variable to another CSV file using Beanshell go for Sampler Variables property instead.
Add the next line to the end of 2nd PostProcessor:
vars.put("delta", String.valueOf(delta));
Add the following line to user.properties file (lives in JMeter's "bin" folder)
sample_variables=delta
On next JMeter restart you will see a new column having "delta" variable value in .jtl results file.
Another approach of setting Sample Variables property is passing it via -J command line argument as:
jmeter -Jsample_variables=delta,somethingelse -n -t testplan.jmx -l results.jtl
See Apache JMeter Properties Customization Guide for more information using, setting and overriding this and other JMeter properties.
You can also use Flexible File Writer for that (you will still need Sample Variables).