How to clear header manager programmatically - jmeter

Question

I have a TestPlan
Thread-group
HttpSampler
pre-processor
HttpHeaderManager[empty]
HttpRequestDefaults[empty]
Post-processor
I am using a pre-processor script to add headers dynamically to headerManager from reading a json file. it goes well .
import org.apache.jmeter.protocol.http.control.Header
int min = args[0].toInteger()
int max = args[1].toInteger()
int random = min + (int) (Math.random() * ((max - min) + 1));
// here 'inputjson' referring to slurped json object
inputjson.Headers.each{
it.each{ key,value -> sampler.getHeaderManager().add(new Header(key.replace('$random',random.toString()),value.replace('$random',(random+2).toString())));
}
}
the issue is, if a thread loop count is 3, then the set of headers are adding 3 times.
then I added a post processor script
sampler.getHeaderManager().clear()
This time initial[loop-1] run is going fine, next[loop-2] loop is a clear request with no headers. how can I achieve, each request will go with only 1 set of headers

Answer 1

Here is my working example - HeaderManager.clear() did not work, but removing the header by its name did its job.
import org.apache.jmeter.protocol.http.control.Header;
sampler.getHeaderManager().removeHeaderNamed("Authorization");
sampler.getHeaderManager().add(new Header("Authorization", "Bearer " + vars.get("token")));

Answer 2

You can use below code to remove headers programatically - first, getting the headers count and looping till the end of headers count.
int headers_size = sampler.getHeaderManager().size();
log.info("headers_size: "+ headers_size);
while(headers_size > 0) {
log.info("header to be removed:"+ sampler.getHeaderManager().get(0));
sampler.getHeaderManager().remove(0);
headers_size = sampler.getHeaderManager().size();
}

Answer 3

This will done by
adding sampler.setHeaderManager(new HeaderManager()) just before the headerManger add section .
each time a new HeaderManger will get added and will be used. Not sure it is the best solution , but its a working solution.

Answer 4

Don't use the f$%$ing method HeaderManager.clear() which existence I still don't get, and do not do that in a post-processor, better do this in your preprocessor before adding headers to Header Manager.
headerMgr = sampler.getHeaderManager();
while(headerMgr.getHeaders().iterator().hasNext()) {
headerName = headerMgr.getHeaders().iterator().next().getStringValue().split("\\s+")[0];
headerMgr.removeHeaderNamed(headerName);
}