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= Compiling Groovy

[[section-groovyc-compiler]]
== 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:

[cols="<,<,<,<",options="header,footer"]
|=======================================================================
| Short version | Long version | Description | Example
| -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)|
| | --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
| @argfile | | Read options and source files from specified file. | groovyc @conf/args
|=======================================================================

*Notes:*
* for a full description of joint compilation, see <<section-jointcompilation,the joint compilation section>>.

== Ant task

See the <<groovyc-ant-task.adoc#ThegroovycAntTask-groovyc,groovyc Ant task>> documentation.
It allows the Groovy compiler to be invoked from http://ant.apache.org/[Apache Ant].

[[Gant]]
== Gant
https://github.com/Gant/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.

[[Gradle]]
== Gradle
http://www.gradle.org/[Gradle] is a build tool that allows you to leverage the
flexibility of http://ant.apache.org/[Ant], while keeping the simplicity of
convention over configuration that tools like http://maven.apache.org/[Maven]
offer. Builds are specified using a Groovy DSL, which offers great flexibility
and succinctness.

== Maven integration
There are several approaches to compiling Groovy code in your Maven
projects. <<section-gmavenplus,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
<<section-gmaven,GMaven>> and <<Gradle>> can have issues).
The <<section-groovyeclipse,Groovy-Eclipse compiler plugin for Maven>>
sidesteps the joint compilation issues. Read
https://github.com/groovy/groovy-eclipse/wiki/Groovy-Eclipse-Maven-plugin#why-another-groovy-compiler-for-maven-what-about-gmaven[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.

[source,xml]
--------------------------------------------------------------------------------------------------------
<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.

=== GMaven and GMavenPlus
[[section-gmaven]]
==== GMaven
https://github.com/groovy/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 <<section-jointcompilation,joint compilation>>.
<<section-gmavenplus,GMavenPlus>> can be a good replacement, but if you
are having problems with joint compilation, you might consider the
<<section-groovyeclipse,Groovy Eclipse maven plugin>>.

[[section-gmavenplus]]
==== GMavenPlus

https://github.com/groovy/GMavenPlus[GMavenPlus] is a rewrite of
<<section-gmaven,GMaven>> and is in active development. It supports most of the
features of GMaven (a couple notable exceptions being
http://maven.apache.org/plugin-tools/maven-plugin-tools-java/index.html[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.

[[section-gmaven2]]
==== GMaven 2

Unlike the name might seem to suggest, http://groovy.github.io/gmaven/[GMaven 2]
is not aimed at replacing <<section-gmaven,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.

[[section-groovyeclipse]]
=== The Groovy Eclipse Maven plugin

https://github.com/groovy/groovy-eclipse/wiki/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.

[[section-jointcompilation]]
== 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 there are a number of places where semantics could be different.

[[section-android]]
== 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
<<section-groovyc-compiler,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 https://github.com/groovy/groovy-android-gradle-plugin[Gradle plugin] adds
support for the Groovy language in the Android Gradle toolchain.

The plugin can be applied like this:

```groovy

buildscript {
    repositories {
        jcenter()
    }
    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:

```groovy
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:

```groovy
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 https://github.com/groovy/groovy-android-gradle-plugin[plugin homepage] in order to
find the latest documentation and version.