1. Groovy : Groovy Console

The Groovy Swing Console allows a user to enter and run Groovy scripts. This page documents the features of this user interface.

2. Basics


  1. Groovy Console is launched via groovyConsole or groovyConsole.bat, both located in $GROOVY_HOME/bin

  2. The Console has an input area and an output area.

  3. You type a Groovy script in the input area.

  4. When you select Run from the Actions menu, the console compiles the script and runs it.

  5. Anything that would normally be printed on System.out is printed in the output area.

  6. If the script returns a non-null result, that result is printed.

3. Features

3.1. Command-line Options and Arguments

The Groovy Console supports several options to control classpath and other features.

./bin/groovyConsole --help
Usage: groovyConsole [options] [filename]
The Groovy Swing Console allows a user to enter and run Groovy scripts.
      --configscript=PARAM   A script for tweaking the compiler configuration options
      -cp, -classpath, --classpath
                             Specify where to find the class files - must be first
  -D, --define=<name=value>  Define a system property
  -h, --help                 Display this help message
  -i, --indy                 Enable InvokeDynamic (Indy) compilation for scripts
  -pa, --parameters          Generate metadata for reflection on method parameter
                               names (jdk8+ only)
  -pr, --enable-preview             Enable preview Java features (JEP 12) (jdk12+ only)
  -V, --version              Display the version

3.2. Running Scripts

There are several shortcuts that you can use to run scripts or code snippets:

  • Ctrl+Enter and Ctrl+R are both shortcut keys for Run Script.

  • If you highlight just part of the text in the input area, then Groovy runs just that text.

  • The result of a script is the value of the last expression executed.

  • You can turn the System.out capture on and off by selecting Capture System.out from the Actions menu

3.3. Editing Files

You can open any text file, edit it, run it (as a Groovy Script) and then save it again when you are finished.

  • Select File > Open (shortcut key ctrl+O) to open a file

  • Select File > Save (shortcut key ctrl+S) to save a file

  • Select File > New File (shortcut key ctrl+Q) to start again with a blank input area

3.4. History and results

  • You can pop-up a gui inspector on the last (non-null) result by selecting Inspect Last from the Actions menu. The inspector is a convenient way to view lists and maps.

  • The console remembers the last ten script runs. You can scroll back and forth through the history by selecting Next and Previous from the Edit menu. Ctrl-N and ctrl-P are convenient shortcut keys.

  • The last (non-null) result is bound to a variable named _ (an underscore).

  • The last result (null and non-null) for every run in the history is bound into a list variable named (two underscores). The result of the last run is [-1], the result of the second to last run is __[-2] and so forth.

3.5. Interrupting a script

The Groovy console is a very handy tool to develop scripts. Often, you will find yourself running a script multiple times until it works the way you want it to. However, what if your code takes too long to finish or worse, creates an infinite loop? Interrupting script execution can be achieved by clicking the interrupt button on the small dialog box that pops up when a script is executing or through the interrupt icon in the tool bar.


However, this may not be sufficient to interrupt a script: clicking the button will interrupt the execution thread, but if your code doesn’t handle the interrupt flag, the script is likely to keep running without you being able to effectively stop it. To avoid that, you have to make sure that the Script > Allow interruption menu item is flagged. This will automatically apply an AST transformation to your script which will take care of checking the interrupt flag (@ThreadInterrupt). This way, you guarantee that the script can be interrupted even if you don’t explicitly handle interruption, at the cost of extra execution time.

3.6. And more

  • You can change the font size by selecting Smaller Font or Larger Font from the Actions menu

  • The console can be run as an Applet thanks to groovy.ui.ConsoleApplet

  • Code is auto indented when you hit return

  • You can drag’n’drop a Groovy script over the text area to open a file

  • You can modify the classpath with which the script in the console is being run by adding a new JAR or a directory to the classpath from the Script menu

  • Error hyperlinking from the output area when a compilation error is expected or when an exception is thrown

  • You can enable InvokeDynamic (Indy) compilation mode by selecting Enable Indy Compilation from the Script menu

4. Embedding the Console

To embed a Swing console in your application, simply create the Console object, load some variables, and then launch it. The console can be embedded in either Java or Groovy code. The Java code for this is:

import groovy.ui.Console;

    Console console = new Console();
    console.setVariable("var1", getValueOfVar1());
    console.setVariable("var2", getValueOfVar2());

Once the console is launched, you can use the variable values in Groovy code.

5. Visualizing script output results

You can customize the way script output results are visualized. Let’s see how we can customize this. For example, viewing a map result would show something like this:


What you see here is the usual textual representation of a Map. But, what if we enabled custom visualization of certain results? The Swing console allows you to do just that. First of all, you have to ensure that the visualization option is ticked: View → Visualize Script Results — for the record, all settings of the Groovy Console are stored and remembered thanks to the Preference API. There are a few result visualizations built-in: if the script returns a java.awt.Image, a javax.swing.Icon, or a java.awt.Component with no parent, the object is displayed instead of its toString() representation. Otherwise, everything else is still just represented as text. Now, create the following Groovy script in ~/.groovy/OutputTransforms.groovy:

import javax.swing.*

transforms << { result ->
    if (result instanceof Map) {
        def table = new JTable(
            result.collect{ k, v ->
                [k, v?.inspect()] as Object[]
            } as Object[][],
            ['Key', 'Value'] as Object[])
        table.preferredViewportSize = table.preferredSize
        return new JScrollPane(table)

The Groovy Swing console will execute that script on startup, injecting a transforms list in the binding of the script, so that you can add your own script results representations. In our case, we transform the Map into a nice-looking Swing JTable. We’re now able to visualize maps in a friendly and attractive fashion, as the screenshot below shows:


6. Advanced debugging: AST browser

Groovy Console can visualize the AST (Abstract Syntax Tree) representing the currently edited script, as shown by the screenshot below. This is useful when you want to understand how an AST transformation is working and particularly handy if you are developing your own AST transform. In the example below, we have annotated our class with the @Immutable annotation and the Groovy compiler has generated a lot of boilerplate code for us. We can see the code for the generated equals method in the Source tab.

AST Browser

We can even examine the JVM bytecode generated by the compiler. In the image below we are looking at the bytecode for the Groovy expression LocalDate.parse('2020/02/10', 'yyyy/MM/dd').

AST Browser

7. Advanced debugging: CST browser

Groovy Console can visualize the CST (Concrete Syntax Tree) representing the initial parsing of the script. This is mainly useful for parsing gurus.

CST Browser