---
title: "JMeter JSR223 Groovy Script Errors & Exceptions"
description: "Fix JMeter JSR223 Groovy script errors: ScriptException, MissingPropertyException, null pointer errors, vars vs props scope, and compilation caching."
url: https://docs.jmeter.ai/topics/errors/jsr223-groovy-script-errors/
lastUpdated: 2026-10-18
source: docs.jmeter.ai
---

# JMeter JSR223 Groovy Script Errors & Exceptions

## Symptom

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

```text
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:

```text
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:

```groovy
// ❌ 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:

```groovy
// 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`:

```groovy
// 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:

```groovy
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](/topics/errors/metaspace-gc-overhead-limit/) | Fixing Metaspace leaks caused by Groovy scripts |
| [Functions and variables](/topics/functions-and-variables/) | Built-in JMeter functions guide |
| [Correlation & dynamic values](/topics/correlation-dynamic-values/) | Extracting and passing dynamic values |
| [Best practices](/user-manual/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

→

### Next Practical Step

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

📖

### Related Reference

- [Functions and variables](/topics/functions-and-variables/)
- [Correlation & dynamic values](/topics/correlation-dynamic-values/)
- [Best practices](/user-manual/best-practices/)