Pre Processor Elements

                 The Pre Processor elements are used to modify the sampler requests before their processing(hence the name pre-processor).

How to add a Pre Processors in JMeter-

step 1:Right Click on either of Thread Group/Logic Controller

step 2: Add -> Hover Over 'Pre Processors' and Click on the required Pre Processor Element

you can refer the same in the following screenshot.

                    The pre processors in jmeter are beanshell pre processor , BSF preprocessor ,HTML link parser ,JDBC preprocessor , Regex user parameters , sample timed out and user parameters.

BeanShell PreProcessor

The BeanShell preprocessor is used to perform some operation using beanshell scripting before a sampler request.

HTML Link Parser

The HTML Link Parser is used to extract links from HTML response fetched from server.

HTTP URL Re-writing Modifier The HTTP URL Re-writing modifier can be added at either Thread Group level or Sampler level to fetch a specific sessionID parameter from the response of a request and then use the parameter's value on other requests.

JSR223 PreProcessor

The JSR223 preprocessor is used to perform some operation using JSR223 scripting before a sampler request.

JDBC PreProcessor

The JDBC PreProcessor is used to execute certain specified SQL queries before a sampler request processing.

RegEx User Parameters

The RegEx user parameters are used to extract HTTP parameters from certain request using a regular expression and then passed as request parameter to other sampler requests.

User Parameters

The User parameters are used to specify values for User variables used within Thread Groups.