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Groovy tips and tricks


This section provides additional tips and tricks when using Groovy as the scripting language for your mocks. It builds on the Scripting documentation. If you are new to Imposter scripting, it's best to start there.

Debugging Groovy scripts

See the debugging Groovy scripts documentation.

Block syntax for respond

Groovy users can use this special block syntax, for improved readability:

respond {
    // behaviours go here

For example:

respond {
    withStatusCode 201

Parsing JSON

To parse JSON in the request, you can use the Groovy JsonSlurper class in your scripts.

Here's a working example:

# imposter-config.yaml
plugin: rest

- path: /
  method: POST
  scriptFile: json-parse.groovy
// json-parse.groovy

def parser = new groovy.json.JsonSlurper()
def json = parser.parseText(context.request.body)



$ curl -X POST  http://localhost:8080 -d '{ "hello": "world" }'

Dynamically loading other Groovy scripts

You can dynamically include another Groovy script file in your script code.

Warning: An important consideration with dynamic script inclusion is performance. Normally, when Imposter sees a script file referenced from config, it precompiles it on startup, so that executions of the script are faster. Depending on machine resources, script size, and other factors script execution can be 10x-100x slower without precompilation.

If you want to include Groovy scripts dynamically, then you can do something like this:

// entrypoint.groovy

def other = loadDynamic('/path/to/other-script.groovy')


then in the referenced file you'd have something like:

// other-script.groovy
// this file is included from 'entrypoint.groovy'

int getStatusCode() {
    return 201

Note that the result of calling the loadDynamic(..) method is a new Groovy script object. Specifically, the GroovyClassLoader returns a subclass of groovy.lang.Script.

This object does not share global state ('bindings') with the calling script, so it doesn't have access to DSL functions like respond() etc.

A work-around is use the dynamically-loaded scripts to do computation/logic and return an object for your dispatcher to then use when it calls respond().

Adding a JAR file to the classpath for Groovy scripts

You can add a JAR file to the classpath for Groovy scripts by adding it to the plugins directory. This will be added to the classpath when the Groovy script is executed.

To do this:

  1. create a directory containing the JAR file
  2. set the IMPOSTER_PLUGIN_DIR environment variable (or set plugin.dir in your .imposter.yaml file in the config directory) to the path above

Improved Groovy DSL support in your IDE

For more sophisticated script development, you can set up a project in your IDE with improved code assistance. You can use this alongside the debugger for a fully integrated development experience.

This requires setting up a project with a dependency on imposter-api.jar and adding the GroovyDSL (GDSL) file.

➡️ See an example project

If you just want to download the GDSL file see:

➡️ Download the GDSL file