Top 30 JMeter Interview Questions

JMeter is one of the Java tools which is used to perform load testing client/server applications. Apache JMeter is open source software, a 100% pure Java desktop application designed to load test functional behaviour and measure performance of the application.

JMeter acts like a group of users sending requests to a target server. It collects response from target server and other statistics which show the performance of the application or server via graphs or tables.

Regular Expressions are used to search and manipulate text. JMeter is used for interpreting forms of regular expression or patterns being used throughout a JMeter test plan.

The protocols supported by JMeter are:

Web: HTTP, HTTPS sites ‘web 1.0’ web 2.0
Web Services: SOAP / XML-RPC
Database via JDBC drivers
Directory: LDAP
Messaging Oriented service via JMS
Service: POP3, IMAP, SMTP
FTP Service

A Test Plan provides a layout of the web application as well as the client-server application. It can be viewed as a container for running tests. A complete test plan will consist of one or more elements such as thread groups, logic controllers, sample-generating controllers, listeners, timers, assertions, and configuration elements. A test plan must have at least one thread group.

Samplers – Sampler generates one or more sample results. These sample results have many attributes like elapsed time, data size, etc. It allows JMeter to send specific types of requests to the server, through samplers, thread group decides which type of request it need to make. Some of the useful samplers are HTTP request, FTP request, JDBC request etc.

Thread Groups – JMeter is the beginning part of thread group elements. It is an important element of JMeter, where you can set number of users and time to load all the users given in the thread group.

The two types of JMeter are:

Pre-processor
Post processor

A pre-processor is something that will happen before sampler executes. To configure the sample request prior to its execution or to update variables that are not extracted from response text pre-processor elements are used.

Some of the pre-processor elements include:

HTTP URL re-writing modifier
HTTP user parameter modifier
HTML link parser
BeanShell PreProcessor

A JMeter thread by default will send requests continuously without any pause. Timers are used to get a pause between the request.

The different types of Timer in JMeter are:

Constant Timer – This element delays each request in a Thread Group for the same amount of time.
Gaussian Timer – This element is used to delay each user request for a random period of time.
Synchronizing Timer – This element is used to release number of threads at given point.
Uniform Random Timer – This element is used to delay each request for a random period of time.

Test fragment is a type of element like Thread Group element. The only difference is test fragment is not implemented unless it is referenced by either a Module controller or an Include controller.

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