In JMeter, BeanShell is a scripting language that allows you to write custom code snippets and scripts to extend the functionality of your test plans. It is an integral part of JMeter and provides a flexible way to perform various tasks that may not be achievable using the standard JMeter elements.

Key features of BeanShell in JMeter include:

1. Scripting Language: BeanShell is a scripting language based on Java syntax. This means you can use standard Java code in BeanShell scripts, making it easy for Java developers to work with.
2. Dynamic Test Data Generation: You can generate dynamic test data on the fly using BeanShell scripts. This is helpful when you need unique data for each virtual user in your load test.
3. Custom Authentication and Headers: BeanShell scripts can be used to implement custom authentication mechanisms, especially for token-based authentication or custom headers, by setting the required headers or tokens for subsequent requests.
4. Complex Logic and Calculations: You can perform complex calculations or logic using BeanShell scripts, which may not be achievable using JMeter’s built-in functions or expressions.
5. Data Parameterization: BeanShell allows you to read data from external sources like CSV files or databases and set this data in JMeter variables for use in subsequent requests.
6. Custom Assertions: You can create custom assertions using BeanShell scripts to validate complex response data or to perform custom checks that are not available through built-in JMeter assertions.
7. Debugging and Logging: BeanShell scripts can be used to log custom messages and debugging information during test execution to aid in troubleshooting and understanding the test behavior.
8. Error Handling: You can customize error handling in your test plan using BeanShell scripts to handle exceptions or errors gracefully and set specific error messages or response statuses.

BeanShell can be used in various elements of JMeter, such as Preprocessor, Postprocessor, Timers, Assertions, and more. It provides a powerful way to customize the behavior of your test plans and perform advanced scripting tasks. However, it is essential to use Beanshell judiciously and efficiently, as excessive use of scripting can impact performance. If you are using JMeter 3.1 or later, consider using Groovy scripting instead of Beanshell for better performance and more advanced scripting capabilities.

BeanShell scripting capability can be used with various elements to extend and customize your test plans. The types of BeanShell processors in JMeter include:

1.BeanShell PreProcessor: This element allows you to execute a BeanShell script before each sampler in a specific scope (Thread Group or Sampler). It is typically used to modify or prepare the request data before it is sent.

2.BeanShell PostProcessor: This element allows you to execute a BeanShell script after each sampler in a specific scope (Thread Group or Sampler). It is used to extract or process response data after receiving the server’s response.

3.BeanShell Assertion: This element allows you to create custom assertions using BeanShell scripts to validate response data or check specific conditions. It provides more flexibility than built-in JMeter assertions.

4.BeanShell Timer: This element allows you to introduce delays (timers) between requests using BeanShell scripts. It is useful when you need to implement custom pacing or dynamic wait times.

5.BeanShell Sampler: This element allows you to execute a custom BeanShell script as a sampler. Unlike other samplers that perform HTTP or other protocol requests, this sampler gives you complete control over what the script does.

6.BeanShell Listener: This element allows you to execute a BeanShell script as a listener. It is used to perform custom actions at the end of a test run, such as generating custom reports or performing data analysis.

Below are the use case where you can use in JMeter.

1.Printing Messages to JMeter Log:

log.info("Your message here");

2.Setting and Reading JMeter Variables:

// Set a variable vars.put("variable_name", "variable_value"); 
// Read a variable String value = vars.get("variable_name");

3.Extracting Data from a Response using Regular Expressions:

import java.util.regex.Pattern;
 import java.util.regex.Matcher; 

String responseData = prev.getResponseDataAsString(); 
Pattern pattern = Pattern.compile("regex_pattern_here");
 Matcher matcher = pattern.matcher(responseData); 
if (matcher.find())
 { String extractedValue = matcher.group(1); 
// Change the group index as needed
 vars.put("extracted_value", extractedValue); 
}

4.Simulating Random Wait Times:

import java.util.Random; 

int minWaitTime = 1000;
 // Minimum wait time in milliseconds
 int maxWaitTime = 5000; 
// Maximum wait time in milliseconds 
Random random = new Random(); 
int waitTime = random.nextInt(maxWaitTime - minWaitTime + 1) + minWaitTime;
 Thread.sleep(waitTime);

5.Conditional Execution of Samplers:

if (condition)
 { // Your sampler or code here }

6.Custom Error Handling:

if (errorCondition)
 {
 // Mark the sampler as failed 
SampleResult.setSuccessful(false);
 SampleResult.setResponseMessage("Custom error message"); 
} 
else
 {
 // Mark the sampler as successful 
SampleResult.setSuccessful(true); 
}

7.Reading Properties from JMeter Properties File:

String propertyValue = props.getProperty("property_name");

8.Dynamic Request Payloads:

Use Beanshell to generate dynamic request payloads, especially for SOAP or REST API testing. You can read data from external files or databases and construct the request payload accordingly.

// Read data from a CSV file
String dataFilePath = "path_to_csv_file";
File dataFile = new File(dataFilePath);
BufferedReader reader = new BufferedReader(new FileReader(dataFile));
String line;
StringBuilder payload = new StringBuilder();

while ((line = reader.readLine()) != null) {
    // Construct the payload
    payload.append(line).append("\n");
}

// Set the dynamic payload to the request
sampler.setPostBodyRaw(true);
sampler.addNonEncodedArgument("", payload.toString(), "");

9.Custom Authentication

Implement custom authentication mechanisms using Beanshell for testing applications with unique authentication requirements. This is particularly useful when handling token-based authentication or custom headers.

String username = "your_username";
String password = "your_password";

// Base64 encode username and password
String authValue = username + ":" + password;
String encodedAuth = new String(Base64.encodeBase64(authValue.getBytes()));

// Set the Authorization header
sampler.addHeader("Authorization", "Basic " + encodedAuth);

10.Dynamic URL Parameters:

Use Beanshell to dynamically update URL parameters based on test conditions or extracted data from previous responses.

String dynamicParam = "your_dynamic_value";
String existingURL = sampler.getUrl().toString();
String updatedURL = existingURL + "?param=" + dynamicParam;
sampler.setDomain(updatedURL);

11.Custom Data Validation:

Implement custom data validation logic using Beanshell. For example, you can compare data from the response against an expected value or perform complex validations based on multiple response fields.

String expectedValue = "expected_value";
String actualValue = prev.getResponseDataAsString();

if (actualValue.equals(expectedValue)) {
    // Validation passed
    SampleResult.setResponseOK();
} else {
    // Validation failed
    SampleResult.setResponseMessage("Validation failed: expected " + expectedValue + ", but got " + actualValue);
    SampleResult.setSuccessful(false);
}

12.Handling Exceptions:

Beanshell can be used to print custom debugging information during test execution to get more insights into your test behavior.

log.debug("Debug message: " + someVariable);

13.Dynamic User Credentials from CSV:

If you have a CSV file with user credentials, you can use Beanshell to read the file and assign unique credentials to each virtual user.

String csvFilePath = "path_to_csv_file";
String line;
BufferedReader reader = new BufferedReader(new FileReader(csvFilePath));

while ((line = reader.readLine()) != null) {
    String[] userData = line.split(",");
    String username = userData[0];
    String password = userData[1];

    // Set the credentials for each user
    vars.put("username", username);
    vars.put("password", password);
}

14.Extracting Cookies from a Response:

You can use Beanshell to extract specific cookies from the response and store them in JMeter variables for later use in subsequent requests.

import org.apache.jmeter.protocol.http.control.Cookie;

// Get the response headers
String responseHeaders = prev.getResponseHeaders();

// Parse the response headers to extract cookies
String[] headers = responseHeaders.split("\n");
for (String header : headers) {
    if (header.trim().startsWith("Set-Cookie:")) {
        // Extract the cookie name and value
        String cookieLine = header.trim().substring(11);
        String[] cookieParts = cookieLine.split(";");
        String[] nameValue = cookieParts[0].split("=");
        String cookieName = nameValue[0].trim();
        String cookieValue = nameValue[1].trim();

        // Store the cookie in a JMeter variable
        vars.put(cookieName, cookieValue);
    }
}

15.Manipulating Cookies:

You can use Beanshell to manipulate cookie values before setting them in subsequent requests. For example, you may need to update a specific cookie value based on test conditions.

// Read the existing cookie value
String existingCookie = vars.get("cookie_name");

// Manipulate the cookie value as needed
String updatedCookie = existingCookie + "_modified";

// Set the updated cookie in a JMeter variable for subsequent requests
vars.put("cookie_name", updatedCookie);

16.Setting Cookies for Subsequent Requests:

Use Beanshell to set cookies for subsequent HTTP requests in JMeter. You can get the cookie value from a JMeter variable and then set it in the Cookie Manager.

import org.apache.jmeter.protocol.http.control.Cookie;
import org.apache.jmeter.protocol.http.control.CookieManager;

// Get the cookie value from a JMeter variable
String cookieValue = vars.get("cookie_name");

// Set the cookie in the Cookie Manager
CookieManager manager = sampler.getCookieManager();
Cookie cookie = new Cookie("domain", "cookie_name", cookieValue, "path", false, Long.MAX_VALUE);
manager.add(cookie);

17.Clearing Cookies:

You can use Beanshell to clear cookies before sending requests. This can be useful when you want to start a new session without any previous cookies.

import org.apache.jmeter.protocol.http.control.CookieManager;

// Clear cookies from the Cookie Manager
CookieManager manager = sampler.getCookieManager();
manager.clear();