Noga Cohen is a Sr. Product Marketing Manager for CA BlazeMeter. She manages the BlazeMeter blog and other content activities. Noga focuses on creating technological content in the fields of performance, load testing and API testing, both independently and by managing writers who are developers. Noga has more than 5 years of experience in a wide scope of writing techniques: hi-tech, business, journalist and academic.

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Apr 14 2017

Apache JMeter Functions - An Introduction

Apache JMeter™ functions are values in the JMeter script that enable flexible and more sophisticated management of the test scenarios. Functions dictate operations that can be performed on JMeter variables and constants.


The structure of JMeter functions is:


${__functionName(var1, var2, varN)}


Functions can be used for many different operations, including: inputting information from a file, performing math calculations and value generation, processing strings, evaluating JMeter variables, working with JMeter properties and executing scripts like Javascript or BeanShell script.


This blog post is a quick intro for using JMeter functions. For more detailed information, check out our guides:


Using JMeter Functions - Part I


Using JMeter Functions - Part II


How to Use JMeter Functions - Part III


Or take a look at the complete function guide on the Apache JMeter website.


In this blog post, we will show how to use functions in the JMeter script. We will look at the ThreadNum function and the Information (log) function, as well as at the Function Helper dialog.


We will be testing our regular demo site -


Creating a Basic Test Plan


First, let’s make sure our test works.


1. In the test plan, add ‘serverurl’ as ‘


jmeter test plan serverurl


2. Add a Cookie Manager


Right Click -> Add -> Config Element -> HTTP Cookie Manager


3. Add a Request Defaults element


Right Click -> Add -> Config Element -> HTTP Request Defaults


4. In the Request Defaults Server Name type:


  • Serverurl url variable ${serverurl}
  • Implementation - HTTPClient4
  • Protocol - http


jmeter http request defaults serverurl


5. Add a Thread Group


Right Click -> Add -> Threads -> Thread Group


6. Add a HTTP Sampler as a child element to the Thread Group


Right Click on Thread Group -> Add -> Sampler ->  HTTP Request


7. Add a Listener


Right Click -> Add -> Listener -> View Results Tree


jmeter test scenario


8. Save the script and launch the test to ensure everything is working properly.


jmeter test results view results tree


Now we can add our functions.


JMeter Thread Number Function


The Thread Number function is a function that shows the number of the thread that is being executed. To examine it, let’s modify one of the threads on our test to go through


1. So first, change the number of the threads to a different number, say 3.


jmeter thread group


2. Add an If Controller as a child element to the Thread Group. The If Controller lets us execute requests based on a specific condition.


Right Click on Thread Group -> Add -> Logic Controller -> If Controller


In the Condition, write the JMeter function:


${__threadNum()} == 1


This function refers to the thread that is currently executed, in this case, the first one.


jmeter if controller


4. Add a HTTP Sampler as a child element of the If Controller


Right Click on Thread Group -> Add -> Sampler ->  HTTP Request


5. Type vacation.html in the path field of the HTTP Request. This means we are running the first thread only through the vacation.html page.


jmeter http request functions


6. Save the test, clear the results and run the script


jmeter test scenario


You can see in the results that the vacation page was opened only once, and only for the first thread (we changed the HTTP Request’s name to Vacation, to ensure it was running properly).


jmeter test results threadnum functions


jmeter test results threadnum function


The Information Function and the Function Helper Dialog


The Function Helper Dialog can help you create function strings and see the different function options you have.


1. Open it under JMeter Options, like this:


jmeter function help dialog


2. In the Helper Dialog, you can choose the function you want and see what is required. Let’s look at the information (log) function, which logs a function and returns it in input string.


jmeter log function


3. Fill in the configurations:


  • String to be logged - vacation.html
  • Log level - OUT, this means this string will be printed out to the system log
  • Additional comment - Some comment


jmeter log function configuration


jmeter log function configuration


4. Click on ‘Generate.


You will get the results in the bottom string.


${__log(vacation.html,OUT,,Some comment)}


jmeter log function configuration


Now, you can copy and paste it wherever you need it in your script.


5. We will put it in the path field of the HTTP Request under the If Controller.


jmeter http request log function


6. Save the script, clear previous results, launch the script


7. Check the results and the system outlog. You can see that all the information was printed out in the system log, with the ‘Some comment’.


jmeter log function results in log


Congratulations! You now know have the basic knowledge to start working with JMeter functions. BlazeMeter enhances JMeter tests. You can start testing now, just put your URL or JMX file in the box:


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