The Scala plugin extends the Java plugin to add support for Scala projects. It can deal with Scala-only projects and with mixed Java/Scala projects. It can even deal with Java-only projects. The Scala plugin supports joint compilation of Java and Scala source. This means your project can contain Scala classes which use Java classes, and vice versa.
To use the Scala plugin, include in your build script:
The Scala plugin adds the following tasks to the project.
Table 22.1. Scala plugin - tasks
Task name | Depends on | Type | Description |
compileScala |
compileJava |
ScalaCompile |
Compiles production Scala source files using scalac. |
compileTestScala |
compileTestJava |
ScalaCompile |
Compiles test Scala source files using scalac. |
compile |
compile |
ScalaCompile |
Compiles the given source set's Scala source files using scalac. |
scaladoc |
- | ScalaDoc |
Generates API documentation for the production Scala source files using scaladoc. |
The Scala plugin adds the following dependencies to tasks added by the Java plugin.
Table 22.2. Scala plugin - additional task dependencies
Task name | Depends on |
classes
|
compileScala
|
testClasses
|
compileTestScala
|
|
compile
|
The Scala plugin assumes the project layout shown below. All the Scala source directories can contain Scala and Java code. The Java source directories may only contain Java source code. None of these directories need exist or have anything in them. The Scala plugin will compile whatever it finds, and handles anything which is missing.
Table 22.3. Scala plugin - project layout
Directory | Meaning |
src/main/java
|
Production Java source |
src/main/resources
|
Production resources |
src/main/scala
|
Production Scala source. May also contain Java source for joint compilation. |
src/test/java
|
Test Java source |
src/test/resources
|
Test resources |
src/test/scala
|
Test Scala source. May also contain Java source for joint compilation. |
src/
|
Java source for the given source set |
src/
|
Resources for the given source set |
src/
|
Scala source for the given source set. May also contain Java source for joint compilation. |
The Scala plugin adds a scalaTools
configuration, which it uses to locate the Scala
tools, such as scalac, to use. You must specify the version of Scala to use. Below is an example.
Example 22.3. Declaring the Scala version to use
build.gradle
repositories { mavenCentral() } dependencies { // Libraries needed to run the scala tools scalaTools 'org.scala-lang:scala-compiler:2.8.1' scalaTools 'org.scala-lang:scala-library:2.8.1' // Libraries needed for scala api compile 'org.scala-lang:scala-library:2.8.1' }
The Scala plugin adds the following convention properties to each source set in the project. You can use these properties in your build script as though they were properties of the source set object (see Section 18.2, “Using the convention object”).
Table 22.4. Scala plugin - source set properties
Property name | Type | Default value | Description |
scala
|
SourceDirectorySet (read-only)
|
Not null |
The Scala source files of this source set. Contains all .scala and
.java files found in the Scala source directories, and excludes all other
types of files.
|
scala.srcDirs
|
Set<File> . Can set using anything described in Section 15.5, “Specifying a set of input files”.
|
[
|
The source directories containing the Scala source files of this source set. May also contain Java source files for joint compilation. |
allScala
|
FileTree (read-only)
|
Not null |
All Scala source files of this source set. Contains only the .scala files
found in the Scala source directories.
|
These convention properties are provided by a convention object of type ScalaSourceSet
.
The Scala plugin also modifies some source set properties:
Table 22.5. Scala plugin - source set properties
Property name | Change |
allJava
|
Adds all .java files found in the Scala source directories. |
allSource
|
Adds all source files found in the Scala source directories. |
The Scala plugin includes support for fsc,
the Fast Scala Compiler. fsc
runs in a separate daemon process and can speed up
compilation significantly.
Example 22.4. Enabling the Fast Scala Compiler
build.gradle
compileScala { scalaCompileOptions.useCompileDaemon = true // optionally specify host and port of the daemon: scalaCompileOptions.daemonServer = "localhost:4243" }
Note that fsc
expects to be restarted whenever the contents of its
compile class path change. (It does detect changes to the compile class path itself.) This makes it
less suitable for multi-project builds.