Chapter 6. Java Quickstart

Usually, a Java project will have some dependencies on external JAR files. To reference these JAR files in the project, you need to tell Gradle where to find them. In Gradle, artifacts such as JAR files, are located in a repository. A repository can be used for fetching the dependencies of a project, or for publishing the artifacts of a project, or both. For this example, we will use the public Maven repository:

repositories {
    mavenCentral()
}

Let's add some dependencies. Here, we will declare that our production classes have a compile-time dependency on commons collections, and that our test classes have a compile-time dependency on junit:

dependencies {
    compile group: 'commons-collections', name: 'commons-collections', version: '3.2'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

You can find out more in Chapter 21, Dependency Management.

The Java plugin adds a number of properties to your project. These properties have default values which are usually sufficient to get started. It's easy to change these values if they don't suit. Let's look at this for our sample. Here we will specify the version number for our Java project, along with the Java version our source is written in. We also add some attributes to the JAR manifest.

sourceCompatibility = 1.5
version = '1.0'
manifest.mainAttributes(
    'Implementation-Title': 'Gradle Quickstart',
    'Implementation-Version': version
)

The tasks which the Java plugin adds are regular tasks, exactly the same as if they were declared in the build file. This means you can use any of the mechanisms shown in earlier chapters to customise these tasks. For example, you can set the properties of a task, add behaviour to a task, change the dependencies of a task, or replace a task entirely. In our sample, we will configure the test task, which is of type Test , to add a system property when the tests are executed:

test {
    options.systemProperties['property'] = 'value'
}

Usually the JAR file needs to be published somewhere. To do this, you need to tell Gradle where to publish the JAR file. In Gradle, artifacts such as JAR files are published to repositories. In our sample, we will publish to a local directory. You can also publish to a remote location, or multiple location.

uploadArchives {
    repositories {
       flatDir(dirs: file('repos'))
    }
}

To publish the JAR file, run gradle uploadArchives.

To import your project into Eclipse, simply run gradle eclipse. More on eclipse task can be found in Section 15.14, “Eclipse”.

Here's the complete build file for our sample:

usePlugin 'java'

sourceCompatibility = 1.5
version = '1.0'
manifest.mainAttributes(
    'Implementation-Title': 'Gradle Quickstart',
    'Implementation-Version': version
)

repositories {
    mavenCentral()
}

dependencies {
    compile group: 'commons-collections', name: 'commons-collections', version: '3.2'
    testCompile group: 'junit', name: 'junit', version: '4.+'
}

test {
    options.systemProperties['property'] = 'value'
}

uploadArchives {
    repositories {
       flatDir(dirs: file('repos'))
    }
}

To define a multi-project build, you need to create a settings file. The settings file lives in the root directory of the source tree, and specifies which projects to include in the build. It must be called settings.gradle. For this example, we are using a simple hierarchical layout. Here is the corresponding settings file:

include "shared", "api", "services:webservice"

You can find out more about the settings file in Chapter 24, Multi-project Builds.

For most multi-project builds, there is some configuration which is common to all projects. In our sample, we will define this common configuration in the root project, using a technique called configuration injection. Here, the root project is like a container and the subprojects method iterates over the elements of this container - the projects in this instance - and injects the specified configuration. This way we can easily define the manifest content for all archives, and some common dependencies:

subprojects {
    usePlugin 'java'

    repositories {
       mavenCentral()
    }

    dependencies {
        testCompile 'junit:junit:4.4'
    }

    group = 'org.gradle'
    version = '1.0'
    manifest.mainAttributes(provider: 'gradle')
}

Notice that our sample applies the Java plugin to each subproject. This means the tasks and configuration properties we have seen in the previous section are available in each subproject. So, you can compile, test, and JAR all the projects by running gradle libs from the root project directory.

You can add dependencies between projects in the same build, so that, for example, the JAR file of one project is used to compile another project. In the api build file we will add a dependency on the JAR produced by the shared project. Due to this dependency, Gradle will ensure that project shared always gets built before project api.

dependencies {
    compile project(':shared')
}

We also add a distribution, that gets shipped to the client:

task dist(type: Zip) {
    dependsOn configurations.runtime.buildDependencies
    files configurations.runtime
    fileSet dir: 'src/dist'
}