# Compiling Groovy

version 2.5.15

## 1. groovyc, the Groovy compiler

`groovyc` is the Groovy compiler command line tool. It allows you to compile Groovy sources into bytecode. It plays the same role as `javac` in the Java world. The easiest way to compile a Groovy script or class is to run the following command:

    groovyc MyClass.groovy

This will produce a `MyClass.class` file (as well as other .class files depending on the contents of the source). `groovyc` supports a number of command line switches:

Short version | Long version | Description | Example
--- | --- | --- | ---
@argfile |  | Read options and source files from specified file. | groovyc @conf/args
-cp | -classpath, --classpath | Specify the compilation classpath. Must be the first argument. | groovyc -cp lib/dep.jar MyClass.groovy
| --sourcepath | Directory where to find source files. Not used anymore. Specifying this parameter will have no effect. |
| --temp | Temporary directory for the compiler |
| --encoding | Encoding of the source files | groovyc --encoding utf-8 script.groovy
| --help | Displays help for the command line groovyc tool | groovyc --help
-d |  | Specify where to place generated class files. | groovyc -d target Person.groovy
-v | --version | Displays the compiler version | groovyc -v
-e | --exception | Displays the stack trace in case of compilation error | groovyc -e script.groovy
-j | --jointCompilation* | Enables joint compilation | groovyc -j A.groovy B.java
-b | --basescript | Base class name for scripts (must derive from Script) |
-indy | --indy | Enables invokedynamic support. Requires Java 7+ | groovyc --indy Person.groovy
| --configscript | Advanced compiler configuration script | groovyc --configscript config/config.groovy src/Person.groovy
-Jproperty=value |  | Properties to be passed to `javac` if joint compilation is enabled | groovyc -j -Jtarget=1.6 -Jsource=1.6 A.groovy B.java
-Fflag |  | Flags to be passed to `javac` if joint compilation is enabled | groovyc -j -Fnowarn A.groovy B.java
-pa | --parameters | Generates metadata for reflection on method parameter names. Requires Java 8+. | groovyc --parameters Person.groovy
-pr | --enable-preview | Enable preview Java features (JEP 12) (jdk12+ only). | groovy --enable-preview Person.groovy

Notes: * for a full description of joint compilation, see the joint compilation section.

## 2. Ant task

### 2.1. `<groovyc>`

#### 2.1.1. Description

Compiles Groovy source files and, if joint compilation option is used, Java source files.

#### 2.1.2. Required taskdef

Assuming the groovy jars are in groovy.libs, you will need to declare this task at some point in the `build.xml` prior to the `groovyc` task being invoked.

    <taskdef name="groovyc" classname="org.codehaus.groovy.ant.Groovyc">
      <classpath>
        <fileset file="${groovy.libs}/groovy-ant-VERSION.jar"/>
        <fileset file="${groovy.libs}/groovy-VERSION.jar"/>
      </classpath>
    </taskdef>

#### 2.1.3. <groovyc> Attributes

Attribute | Description | Required
--- | --- | ---
errorProperty | The property to set on compilation failure. This property will be set if the compilation fails. | No
srcdir | Location of the Groovy (and possibly Java) source files. | Yes
destdir | Location to store the class files. | Yes
classpath | The classpath to use. | No
classpathref | The classpath to use given as a path references. | No
sourcepath | The sourcepath to use. | No
sourcepathref | The sourcepath to use given as a path reference. | No
encoding | Encoding of source files. | No
verbose | Asks the compiler for verbose output; defaults to no. | No
includeAntRuntime | Whether to include the Ant run-time libraries in the classpath; defaults to yes. | No
includeJavaRuntime | Whether to include the default run-time libraries from the executing VM in the classpath; defaults to no. | No
includeDestClasses | This property controls whether to include the destination classes directory in the classpath given to the compiler. The default value is "true". | No
fork | Whether to execute groovyc using a spawned instance of the JVM; defaults to no. | No
memoryInitialSize | The initial size of the memory for the underlying VM, if using fork mode; ignored otherwise. Defaults to the standard VM memory setting. (Examples: 83886080, 81920k, or 80m) | No
memoryMaximumSize | The maximum size of the memory for the underlying VM, if using fork mode; ignored otherwise. Defaults to the standard VM memory setting. (Examples: 83886080, 81920k, or 80m) | No
failonerror | Indicates whether compilation errors will fail the build; defaults to true. | No
proceed | Inverse alias for failonerror. | No
listfiles | Indicates whether the source files to be compiled will be listed; defaults to no. | No
stacktrace | if true each compile error message will contain a stacktrace | No
indy | Enable compilation with the ``invoke dynamic'' support when using Groovy 2.0 and beyond and running on JDK 7 | No
scriptBaseClass | Sets the base class for Groovy scripts | No
stubdir | Set the stub directory into which the Java source stub files should be generated. The directory need not exist and will not be deleted automatically - though its contents will be cleared unless 'keepStubs' is true. Ignored when forked. | No
keepStubs | Set the keepStubs flag. Defaults to false. Set to true for debugging. Ignored when forked. | No
forceLookupUnnamedFiles | The Groovyc Ant task is frequently used in the context of a build system that knows the complete list of source files to be compiled. In such a context, it is wasteful for the Groovy compiler to go searching the classpath when looking for source files and hence by default the Groovyc Ant task calls the compiler in a special mode with such searching turned off. If you wish the compiler to search for source files then you need to set this flag to true. Defaults to false. | No
configscript | Set the configuration file used to customize the compilation configuration. | No
parameters | Generates metadata for reflection on method parameter names on JDK 8 and above. Defaults to false. | No
previewFeatures | Enables the JEP preview features on JDK 12 and above. Defaults to false. | No
targetBytecode | Sets the bytecode compatibility level. | No
javahome | Sets the `java.home` value to use, default is the current JDK’s home. | No
executable | Sets the name of the java executable to use when invoking the compiler in forked mode, ignored otherwise. | No
scriptExtension | Set the extension to use when searching for Groovy source files. Accepts extensions in the form *.groovy, .groovy or groovy. | No
updatedProperty | The property to set on compilation success. This property will not be set if the compilation fails, or if there are no files to compile. | No

Example:

    <path id="classpath.main">
      <fileset dir="${groovy.libs}" includes="*.jar" excludes="groovy-ant-*.jar"/>
      ...
    </path>
    <groovyc srcdir="${dir.sources}" destdir="${dir.classes}" classpathref="classpath.main"
             fork="true" includeantruntime="false" configscript="config.groovy" targetBytecode="1.8"/>

#### 2.1.4. <groovyc> Nested Elements

element | kind | Required | Replaces Attribute
--- | --- | --- | ---
javac | javac task | No | N/A
src | a path structure | Yes (unless srcdir is used) | srcdir
classpath | a path structure | No | classpath or classpathref

Notes:

- For path structures see for example http://ant.apache.org/manual/using.html#path

- For usages of the `javac` task see https://ant.apache.org/manual/Tasks/javac.html

- The nested `javac` task behaves more or less as documented for the top-level `javac` task. `srcdir`, `destdir`, `classpath`, `encoding` and `parameters` for the nested `javac` task are taken from the enclosing `groovyc` task. If these attributes are specified then they are added, they do not replace. In fact, you should not attempt to overwrite the destination. Other attributes and nested elements are unaffected, for example `fork`, `memoryMaximumSize`, etc. may be used freely.

#### 2.1.5. Joint Compilation

Joint compilation is enabled by using an embedded `javac` element, as shown in the following example:

    <groovyc srcdir="${testSourceDirectory}" destdir="${testClassesDirectory}" targetBytecode="1.8">
      <classpath>
        <pathelement path="${mainClassesDirectory}"/>
        <pathelement path="${testClassesDirectory}"/>
        <path refid="testPath"/>
      </classpath>
      <javac debug="true" source="1.8" target="1.8" />
    </groovyc>

More details about joint compilation can be found in the joint compilation section.

## 3. Gant

Gant is a tool for scripting Ant tasks using Groovy instead of XML to specify the logic. As such, it has exactly the same features as the Groovyc Ant task.

## 4. Gradle

Gradle is a build tool that allows you to leverage the flexibility of Ant, while keeping the simplicity of convention over configuration that tools like Maven offer. Builds are specified using a Groovy DSL, which offers great flexibility and succinctness.

## 5. Maven integration

There are several approaches to compiling Groovy code in your Maven projects. GMavenPlus is the most flexible and feature rich, but like most Groovy compiler tools, it can have difficulties with joint Java-Groovy projects (for the same reason GMaven and Gradle can have issues). The Groovy-Eclipse compiler plugin for Maven sidesteps the joint compilation issues. Read this for a deeper discussion of the benefits and disadvantages of the two approaches.

A third approach is to use Maven’s Ant plugin to compile a groovy project. Note that the Ant plugin is bound to the compile and test-compile phases of the build in the example below. It will be invoked during these phases and the contained tasks will be carried out which runs the Groovy compiler over the source and test directories. The resulting Java classes will coexist with and be treated like any standard Java classes compiled from Java source and will appear no different to the JRE, or the JUnit runtime.

    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
        <modelVersion>4.0.0</modelVersion>
        <groupId>com.mycomp.MyGroovy</groupId>
        <artifactId>MyGroovy</artifactId>
        <packaging>jar</packaging>
        <version>1.0-SNAPSHOT</version>
        <name>Maven Example building a Groovy project</name>
        <dependencies>
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>3.8.1</version>
                <scope>test</scope>
            </dependency>
            <dependency>
                <groupId>org.codehaus.groovy</groupId>
                <artifactId>groovy-all</artifactId>
                <version>2.5.0</version>
                <type>pom</type> <!-- required JUST since Groovy 2.5.0 -->
            </dependency>
        </dependencies>
        <build>
            <plugins>
                <plugin>
                    <artifactId>maven-antrun-plugin</artifactId>
                    <executions>
                        <execution>
                            <id>compile</id>
                            <phase>compile</phase>
                            <configuration>
                                <tasks>
                                    <mkdir dir="${basedir}/src/main/groovy"/>
                                    <taskdef name="groovyc"
                                        classname="org.codehaus.groovy.ant.Groovyc">
                                        <classpath refid="maven.compile.classpath"/>
                                    </taskdef>
                                    <mkdir dir="${project.build.outputDirectory}"/>
                                    <groovyc destdir="${project.build.outputDirectory}"
                                        srcdir="${basedir}/src/main/groovy/" listfiles="true">
                                        <classpath refid="maven.compile.classpath"/>
                                    </groovyc>
                                </tasks>
                            </configuration>
                            <goals>
                                <goal>run</goal>
                            </goals>
                        </execution>
                        <execution>
                            <id>test-compile</id>
                            <phase>test-compile</phase>
                            <configuration>
                                <tasks>
                                    <mkdir dir="${basedir}/src/test/groovy"/>
                                    <taskdef name="groovyc"
                                        classname="org.codehaus.groovy.ant.Groovyc">
                                        <classpath refid="maven.test.classpath"/>
                                    </taskdef>
                                    <mkdir dir="${project.build.testOutputDirectory}"/>
                                    <groovyc destdir="${project.build.testOutputDirectory}"
                                        srcdir="${basedir}/src/test/groovy/" listfiles="true">
                                        <classpath refid="maven.test.classpath"/>
                                    </groovyc>
                                </tasks>
                            </configuration>
                            <goals>
                                <goal>run</goal>
                            </goals>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>
    </project>

This assumes you have a Maven project setup with `groovy` subfolders as peers to the java src and test subfolders. You can use the `java`/`jar` archetype to set this up then rename the java folders to groovy or keep the java folders and just create groovy peer folders. There exists, also a groovy plugin which has not been tested or used in production. After defining the build section as in the above example, you can invoke the typical Maven build phases normally. For example, `mvn test` will execute the test phase, compiling Groovy source and Groovy test source and finally executing the unit tests. If you run `mvn jar` it will execute the jar phase bundling up all of your compiled production classes into a jar after all of the unit tests pass. For more detail on Maven build phases consult the Maven2 documentation.

### 5.1. GMaven and GMavenPlus

#### 5.1.1. GMaven

GMaven is the original Maven plugin for Groovy, supporting both compiling and scripting Groovy.

Important:

You should be aware that GMaven is not supported anymore and can have difficulties with joint compilation. GMavenPlus can be a good replacement, but if you are having problems with joint compilation, you might consider the Groovy Eclipse maven plugin.

#### 5.1.2. GMavenPlus

GMavenPlus is a rewrite of GMaven and is in active development. It supports most of the features of GMaven (a couple notable exceptions being mojo Javadoc tags and support for older Groovy versions). Its joint compilation uses stubs (which means it has the same potential issues as GMaven and Gradle). The main advantages over its predecessor are that it supports recent Groovy versions, InvokeDynamic, Groovy on Android, GroovyDoc, and configuration scripts.

#### 5.1.3. GMaven 2

Unlike the name might seem to suggest, GMaven 2 is not aimed at replacing GMaven. In fact, it removes the non-scripting features of the GMaven plugin. It has not yet had any release and appears to be inactive currently.

### 5.2. The Groovy Eclipse Maven plugin

Groovy-Eclipse provides a compiler plugin for Maven. Using the compiler plugin, it is possible to compile your maven projects using the Groovy-Eclipse compiler. One feature unavailable elsewhere is stubless joint compilation.

## 6. Joint compilation

Joint compilation means that the Groovy compiler will parse the Groovy source files, create stubs for all of them, invoke the Java compiler to compile the stubs along with Java sources, and then continue compilation in the normal Groovy compiler way. This allows mixing of Java and Groovy files without constraint.

Joint compilation can be enabled using the `-j` flag with the command-line compiler, or using using a nested tag and all the attributes and further nested tags as required for the Ant task.

It is important to know that if you don’t enable joint compilation and try to compile Java source files with the Groovy compiler, the Java source files will be compiled as if they were Groovy sources. In some situations, this might work since most of the Java syntax is compatible with Groovy, but semantics would be different.

## 7. Android support

It is possible to write an Android application in Groovy. However this requires a special version of the compiler, meaning that you cannot use the regular groovyc tool to target Android bytecode. In particular, Groovy provides specific JAR files for Android, which have a classifier of `grooid`. In order to make things easier, a Gradle plugin adds support for the Groovy language in the Android Gradle toolchain.

The plugin can be applied like this:

    buildscript {
        repositories {
            mavenCentral()
        }
        dependencies {
            classpath 'com.android.tools.build:gradle:2.1.2'
            classpath 'org.codehaus.groovy:groovy-android-gradle-plugin:1.0.0'
        }
    }

    apply plugin: 'groovyx.android'

Then you will need to add a dependency on the `grooid` version of the Groovy compiler:

    dependencies {
        compile 'org.codehaus.groovy:groovy:2.4.7:grooid'
    }

Note that if a Groovy jar does not provide a `grooid` classifier alternative, then it means that the jar is directly compatible with Android. In that case, you can add the dependency directly like this:

    dependencies {
        compile 'org.codehaus.groovy:groovy:2.4.7:grooid'       // requires the grooid classifier
        compile ('org.codehaus.groovy:groovy-json:2.4.7') {     // no grooid version available
            transitive = false                                  // so do not depend on non-grooid version
        }
    }

Note that the `transitive=false` parameter for `groovy-json` will let Gradle download the JSON support jar without adding a dependency onto the normal jar of Groovy.

Please make sure to go to the plugin homepage in order to find the latest documentation and version.