Using JMeter

JMeter is a Java-based tool for load testing client-server applications. Stefano Mazzocchi originally wrote it to test the performance of Apache JServ (the predecessor of Jakarta Tomcat). It has since become a subproject of Jakarta.

Installing and Running JMeter

The most recent release of JMeter is version 1.8. You can download the latest stable version from JMeter's site. Downloads area available as either .gz or .zip files. JMeter 1.8 requires a working JDK 1.4 environment.

Once you extract the binary distribution file, JMeter is ready for you. On Linux/UNIX, run JMeter by invoking the jmeter shell script. On Windows, call the jmeter.bat file. Both files can be found in the bin/ directory of the JMeter installation directory. Figure 1 shows JMeter's main window, which is a Swing application.

Figure 1: JMeter's main window.

The user interface has two panes. The left pane displays the elements used in our testing. Initially, there are the Root and two sub-elements, Test Plan and WorkBench. In this article we're only concerned with Test Plans. Add an element to a node by right-clicking it and selecting Add. To remove an element, select the element by clicking on it, then right-click on the element and choose the Remove option.

The right pane of the user interface displays the details of each element. You are now ready to use JMeter. There are two things to note:

1. You should not run JMeter on the same machine running the application to be tested. JMeter may use extensive resources that might affect the other application's performance if they are both run on the same machine.
2. Make sure that the testing is affected as little as possible by network traffic. The best thing to do is to ask your network administrator to set up an isolated sub-network for the machine running the Web application and the machine running JMeter.

Using JMeter for a Simple Test

Let's start with a very simple test. In this test, we will set up a test plan and stress test a Web application. You will be introduced with some common concepts in JMeter. After understanding this basic test, you should be able to use all of the capabilities of JMeter.

To conduct a test, you must have a test plan. A test plan describes the steps that JMeter will take to perform the testing. A test plan includes elements such as thread groups, logic controllers, sample generating controllers, listeners, timers, assertions, and configuration elements. Don't worry at this stage if you don't understand what these elements are.

A test plan must have at least one thread group. A thread group is the starting point of a test plan, and it can contain all other JMeter elements. A thread group controls the threads that will be created by JMeter to simulate simultaneous users.

Now, let's start by creating a thread group. Right-click the Test Plan element and select Add and then Thread Group. JMeter will create a thread group element under Test Plan element. Click the Thread Group element, and you will see a screen like the one in Figure 2.

Figure 2: Configuring a thread group.

In this page, you can set the following properties:

• Name -- the name of this thread group. You can give a descriptive name to this property.
• Number of Threads -- the number of threads created. Each thread represents a single user. Therefore, if you want to simulate a load test with 10 concurrent users, enter 10 as the value for this property.
• Ramp-Up Period -- the number of seconds JMeter will take to accelerate to create all of the threads needed. If the number of threads used is 10 and the ramp-up period is 20 seconds, JMeter will take 20 seconds to create those 10 threads, creating one new thread every two seconds. If you want all threads to be created at once, put 0 in this box.
• Forever -- if clicked, this option tells JMeter to keep sending requests to the tested application indefinitely. If disabled, JMeter will repeat the test for the number of times entered in the Loop Count box.
• Loop Count --this property value only has an effect if the Forever check box is unchecked. It tells JMeter the number of times it has to repeat the test.

For our simple test, fill the properties with the values found in Figure 2. We will use two users and each test will be performed three times. We use small numbers here so that we can easily explain the results later; in real load testing, you might want to use higher numbers for these properties.

Next, you need to add the element that represents HTTP requests. To do so, right-click the Thread Group element, and select Add, Sampler, and then HTTP Request. An HTTP Request element will be added to the Thread Group element. Click the HTTP Request element to select it, and you should see a screen similar to Figure 3.

Figure 3: Configuring an HTTP Request element.

On the HTTP Request screen, you configure the HTTP requests that will be used to "hit" your application. Here, you can set the following properties.

• Name -- the name of this HTTP request. The name should be descriptive; remember that it is common to have multiple HTTP Request elements in a thread group.
• Server Name or IP -- the server name or the IP address of the machine running the application being tested.
• Port Number -- the port number used by the application. Normally, a Web application runs on port 80.
• Protocol -- the protocol used, either HTTP or HTTPS.
• Method -- the request method, either GET or POST.
• Path -- the path to the resource that will handle this request.
• Follow Redirects -- follows redirections sent by the Web application, if any.
• Use KeepAlive -- if checked, sends the Connection = Keep-Alive request header. By default, an HTTP 1.1 browser uses Keep-Alive as the value of the Connection header. Therefore, this checkbox should be checked.
• Parameters -- the list of parameters sent with this request. Use the Add and Delete buttons to add and remove parameters.
• Send a file with a request -- simulate a file upload to the Web application.
• Retrieve all images and Java Applets -- download embedded content.