JMeter JSR223 Groovy Script Errors & Exceptions

JSR223 Groovy Script Errors in JMeter

Symptom

When executing JSR223 Samplers, PreProcessors, PostProcessors, or Assertions, samples turn red or errors appear in jmeter.log:

2026-08-18 10:15:32,410 ERROR o.a.j.m.JSR223PostProcessor: Problem in JSR223 script, JSR223 PostProcessor
javax.script.ScriptException: groovy.lang.MissingPropertyException: No such property: token for class: Script1
  at org.codehaus.groovy.jsr223.GroovyScriptEngineImpl.eval(GroovyScriptEngineImpl.java:324)

Or for null pointers when accessing variables:

java.lang.NullPointerException: Cannot invoke method split() on null object
  at Script1.run(Script1.groovy:4)

The error causes the sampler to fail and logs a stack trace for every virtual user thread execution.

Quick diagnosis (TL;DR)

• MissingPropertyException: You referenced an undeclared variable directly (e.g. println token) instead of accessing it via the JMeter variables object (vars.get("token")).
• NullPointerException: vars.get("name") returned null because the variable was never created or an upstream extractor failed to find a match.
• Compilation Cache Full / High CPU: Script text contains \${var} string interpolation instead of using vars.get("var").

Essential JSR223 Implicit Objects Reference

JMeter automatically injects predefined context objects into Groovy scripts:

Object	Class	Scope & Purpose
vars	JMeterVariables	Thread-scoped read/write (vars.get("k"), vars.put("k", "v"), vars.putObject("k", obj))
props	JMeterProperties	Global cross-thread properties (props.get("p"), props.put("p", "v"))
prev	SampleResult	Previous sampler result (prev.getResponseDataAsString(), prev.setSuccessful(false))
sampler	Sampler	Current sampler object (sampler.setName("New Name"))
ctx	JMeterContext	Engine context (ctx.getThreadNum(), ctx.getPreviousResult())
log	Logger	Log4j2 logger (log.info("msg"), log.error("err", exception))

Fix (ordered)

1. Always Use vars.get() and vars.put() (Never Direct Variables)

In Groovy, JMeter variables are not global script variables. Always access them via the vars object:

// ❌ WRONG: Throws MissingPropertyException if not declared in script
String myId = userId;

// ❌ WRONG: String interpolation breaks compilation caching and leaks Metaspace!
String myId = "${userId}";

// ✅ CORRECT: Safe retrieval with null checking
String myId = vars.get("userId");
if (myId != null) {
    vars.put("processedUserId", myId.trim().toUpperCase());
} else {
    log.warn("Variable 'userId' was null! Upstream extractor may have failed.");
}

2. Defensively Handle Null Values

If an upstream JSON Extractor or Regex Extractor fails, vars.get() returns null. Add safe navigation (?.) or explicit null guards:

// Using Groovy safe navigation operator
String rawResponse = prev?.getResponseDataAsString();

String authToken = vars.get("authToken");
if (!authToken) {
    // Fail the sample deliberately with a clear error message
    prev.setSuccessful(false);
    prev.setResponseMessage("Missing required authToken from previous step");
    prev.setResponseCode("500");
    return;
}

3. Share Data Between Different Thread Groups with props

vars are strictly isolated per thread. If Thread Group A extracts a token needed by Thread Group B, use props:

// In Thread Group A (Writer)
props.put("GLOBAL_AUTH_TOKEN", vars.get("authToken"));

// In Thread Group B (Reader)
String globalToken = props.get("GLOBAL_AUTH_TOKEN");
vars.put("localToken", globalToken);

4. Enable Script Caching

In every JSR223 component:

1. Ensure Language is set to groovy.
2. Check Cache compiled script if available.
3. Do not put dynamic values in the script body; use vars.get() or script Parameters:
   • Parameters: \${__threadNum} \${userId}
   • Script access: String p0 = args[0];

5. Parse JSON and XML Safely with Groovy Builders

Use built-in Groovy parsers instead of manual regex string manipulation:

import groovy.json.JsonSlurper
import groovy.json.JsonOutput

try {
    def json = new JsonSlurper().parseText(prev.getResponseDataAsString())
    String itemId = json.data.items[0].id
    vars.put("firstItemId", itemId)
} catch (Exception e) {
    log.error("Failed to parse JSON response: " + e.getMessage(), e)
    prev.setSuccessful(false)
}

Related tools and topics

Resource	Use when
Metaspace & GC overhead	Fixing Metaspace leaks caused by Groovy scripts
Functions and variables	Built-in JMeter functions guide
Correlation & dynamic values	Extracting and passing dynamic values
Best practices	Scripting language performance recommendations

Frequently asked questions

Should I use BeanShell or Groovy for scripting in JMeter?

Always use Groovy (JSR223). Groovy compiles down to native Java bytecode and supports script compilation caching, making it 10x to 50x faster than BeanShell. BeanShell is deprecated for high-load testing.

Why do my changes to vars not appear in other threads?

vars (JMeterVariables) are local to the current thread. To pass data across threads, use props.put("key", value) and props.get("key").

Continue Learning

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Next Practical Step

Audit your JSR223 Groovy scripts to replace \${var} interpolation with vars.get("var") and verify null checks.

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Related Reference

• Functions and variables
• Correlation & dynamic values
• Best practices