Thursday, December 21, 2017

JMeter—Use Extractors (Post-Processor Elements) for Correlation



What Is Correlation


Correlation is the process of capturing and storing the dynamic response (e.g., "Session ID" in the above diagram) from the server and passing it on to subsequent requests. A response is considered dynamic when it can return different data for each iterating request, occasionally affecting successive requests. Correlation is a critical process during performance load test scripting, because if it isn’t handled correctly, your script will become useless.

Correlation is 2-step process:
  1. Parse and extract the dynamic value from the response of a step using a Post Processor element such as:
  2. Refer the extracted value in the request of a subsequent step
    • http://.../.../...?sessionID=${sessionId}#....


How to Use Regular Expression Extractor


Watching above video, you can learn how to create Regular Expression Extractors in JMeter in the following steps:[2]
  1. Create a Test Plan where you want to do dynamic referencing in JMeter
  2. Add Regular Expression Extractor in the Step from where response value(s) needs to be extracted
    • You can use RegExr—an online tool—to learn, build, and test Regular Expressions
  3. Refer the extracted value (referred by Reference Name) in subsequent step(s)
  4. Run and validate it


How to Use CSS/JQuery Extractor





Watching above video, you can learn how to create CSS/JQuery Extractors in JMeter in similar steps:[8]
  1. Create a Test Plan where you want to do dynamic referencing in JMeter
  2. Add CSS/JQuery Extractor[9]in the Step from where response value(s) needs to be extracted
    • You can find a detailed explanation of CSS syntax here. jQuery's selector engine uses most of the same syntax as CSS with some exceptions. For selecting an arbitrary locator, you can use field Match No. with the ‘0’ value, which returns a random value from all found results.
    • It is also worth mentioning there is a list of very convenient browser plugins to test CSS locators right into your browser. For Firefox, you can use the ‘Firebug’ plugin, while for Chrome ‘XPath Helper’ is the most convenient tool.
  3. Refer the extracted value (referred by Reference Name) in subsequent step(s)
  4. Run and validate it


How to Use JSON Extractor


Read the companion articles on this subject:

References

  1. Advanced Load Testing Scenarios with JMeter: Part 1 - Correlations
  2. JMeter Beginner Tutorial 19 - Correlation (with Regular Expression Extractor)
  3. Using RegEx (Regular Expression Extractor) with JMeter
  4. RegExr—an online tool (good)
  5. JMeter Listeners - Part 1: Listeners with Basic Displays
  6. Understand and Analyze Summary Report in Jmeter
  7. How to Automate Auth Token using JMETER
  8. How to Use the CSS/JQuery Extractor in JMeter (BlazeMeter)
  9. How to Use the CSS/jQuery Extractor in JMeter  (DZone)
  10. JMeter: How to Turn Off Captive Portal from the Recording Using Firefox (Xml and More)
  11. JMeter―Select on Multiple Criteria with JSONPath  (Xml and More)
  12. JMeter: How to Verify JSON Response?  (Xml and More)

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