Testing APIs with JMeter

As test engineers, we can use JMeter to script tests against API's, chain them so they actually resemble a real request, even make assertions against responses.


November 05, 2015


Apache JMeter may be used to test performance both on static and dynamic resources, Web dynamic applications.

It can be used to simulate a heavy load on a server, group of servers, network or object to test its strength or to analyze overall performance under different load types.

Apache JMeter features include:

  • Web - HTTP, HTTPS (Java, NodeJS, PHP, ASP.NET, …)
  • SOAP / REST Webservices
  • FTP
  • Database via JDBC
  • LDAP
  • Message-oriented middleware (MOM) via JMS
  • Mail - SMTP(S), POP3(S) and IMAP(S)
  • Native commands or shell scripts
  • TCP
  • Java Objects
  • Full featured Test IDE that allows fast Test Plan recording (from Browsers or native applications), building and debugging.
  • Command-line mode (Non GUI / headless mode) to load test from any Java compatible OS (Linux, Windows, Mac OSX, …)
  • A complete and ready to present dynamic HTML report
  • Easy correlation through ability to extract data from most popular response formats, HTML, JSON , XML or any textual format
  • Complete portability and 100% Java purity.
  • Full multi-threading framework allows concurrent sampling by many threads and simultaneous sampling of different functions by separate thread groups.
  • Caching and offline analysis/replaying of test results.
  • Highly Extensible core:
  • Pluggable Samplers allow unlimited testing capabilities.
  • Scriptable Samplers (JSR223-compatible languages like Groovy and BeanShell) S* everal load statistics may be chosen with pluggable timers.
  • Data analysis and visualization plugins allow great extensibility as well as personalization.
  • Functions can be used to provide dynamic input to a test or provide data manipulation.
  • Easy Continuous Integration through 3rd party Open Source libraries for Maven, Gradle and Jenkins.

JMeter is not a browser, it works at protocol level. As far as web-services and remote services are concerned, JMeter looks like a browser (or rather, multiple browsers); however JMeter does not perform all the actions supported by browsers. In particular, JMeter does not execute the Javascript found in HTML pages. Nor does it render the HTML pages as a browser does (it’s possible to view the response as HTML etc., but the timings are not included in any samples, and only one sample in one thread is ever displayed at a time).

Please make sure to have the latest version of Firefox downloaded.

Charles (Blackbox Testing)

If preferred, locally download Charles. This tool, alongside JMeter, is an equally powerful tool that tells you what exactly is going on. It can even be used to sniff iOS and Android http/https requests, let alone API’s.

As soon as you open Charles and play around outside the app, you’ll notice data being collected in the left-tab. Every HTTP/HTTPS request being made is monitored. So if you’re confused about a call and how it should look in JMeter, when a similar tool is running, you can use this to parse all data collected.

Remote Server or Local

Go to Apache and download the latest binaries. Install and unzip.

Then go to: /bin/ApacheJMeter.jar and open the file. You’ll need Java.

Or for remote in terminal run:

sudo apt-get install jmeter jmeter-http

You should see a bunch of files downloading. Go through the above steps and start ApacheJMeter.

JMeter, locally, should look like:

JMeter Documentation

Sniffing HTTP Requests

  1. Right-click on Test Plan
  2. Add > Logic Controller > Recorder Controller
  3. Right-click on WorkBench
  4. Add > Non-test Elements > HTTP Proxy Server
  5. Open Firefox

    1. Go through restart/install procedure, post-Charles installation
    2. Go to FireFox > Preferences > Advanced

      1. While in Network tab, select Settings for Connection section
      2. Change HTTP Proxy to “localhost:8080” or something not used, note the port being used.
      3. Check “Use this proxy for all protocols”
      4. Save, all websites should fail until Proxy is started
  6. Select HTTP Proxy Server

    1. In the Right, you should see Global Settings (Port: 8080, by default)
    2. Set Port to “8080” or port selected from earlier
    3. On HTTP Proxy Server, click the Add button in “URL Patterns to Include”. This will create a blank entry. Enter “html”.
    4. Click the Add button in URL Patterns to Exclude 3 times. This will create 3 blank entries. After that enter “.png” pattern, “.gif” pattern and “.ico” pattern.
  7. In the HTTP Proxy Server, you should see a Start button on bottom, press it.
  8. In FireFox, go to any website of your choice.

    • Notice the left-pane, similar to Charles.app, JMeter now records all HTTP Requests and all assets being requested. Alongside with paths, JMeter is also recording Headers sent from your machine.

Load Tests

In this example we will run load tests against Google, lets hope they don’t get mad 😺. While having JMeter open:

  1. Right-click on Test Plan
  2. Add > Threads > Thread Group
  3. Rename the Thread Group to “Google.com Users”

    1. Set Number of Threads to “10”
    2. Set Loop Count to “2”
  4. Right-click on Thread Group, Add > Listener > Summary Report
  5. Right-click on “Google.com Users”
  6. Add > Sampler > HTTP Request
  7. Add Server Name, “www.google.com”, Add Path, ”/”, leave everything else empty
  8. Press Play and viola, you’ve ran you’re first Load Test using JMeter

CSV Config Element

In API’s we need to give inputs, there is a way in JMeter to provide inputs from csv file. You can create csv file of your inputs and provide this file to JMeter. JMeter will read your csv file line by line and provide this data to your http request. So how to provide inputs from csv file, it’s pretty simple. Create your csv file, I have created logindetails.csv file. Now right click on thread group and go to Add –> Config Element –> CSV data set Config.