The Java plugin provides a lot of useful tasks and properties we can use for building a Java application or library. If we follow the convention-over-configuration support of the plugin, we don't have to write a lot of code in our Gradle build file to use it. If we want to, we can still add extra configuration options to override the default conventions defined by the plugin.
Let's start with a new build file and use the Java plugin. We only have to apply the plugin for our build:
apply plugin: 'java'
And that's it! By just adding this simple line, we now have a lot of tasks we can use to work with in our Java project. To see which tasks have been added by the plugin, we run the tasks command on the command line and look at the output:
$ gradle tasks :tasks ------------------------------------------------------------ All tasks runnable from root project ------------------------------------------------------------ Build tasks ----------- assemble - Assembles all Jar, War, Zip, and Tar archives. build - Assembles and tests this project. buildDependents - Assembles and tests this project and all projects that depend on it. buildNeeded - Assembles and tests this project and all projects it depends on. classes - Assembles the main classes. clean - Deletes the build directory. jar - Assembles a jar archive containing the main classes. testClasses - Assembles the test classes. Documentation tasks ------------------- javadoc - Generates Javadoc API documentation for the main source code. Help tasks ---------- dependencies - Displays the dependencies of root project 'sample'. help - Displays a help message projects - Displays the sub-projects of root project 'sample'. properties - Displays the properties of root project 'sample'. tasks - Displays the tasks runnable from root project 'sample' (some of the displayed tasks may belong to subprojects). Verification tasks ------------------ check - Runs all checks. test - Runs the unit tests. Rules ----- Pattern: build<ConfigurationName>: Assembles the artifacts of a configuration. Pattern: upload<ConfigurationName>: Assembles and uploads the artifacts belonging to a configuration. Pattern: clean<TaskName>: Cleans the output files of a task. To see all tasks and more detail, run with --all. BUILD SUCCESSFUL Total time: 0.911 secs
If we look at the list of tasks, we can see how many tasks are now available to us that we didn't have before; all this just by adding a simple line to our build file.
We have several task groups with their own individual tasks that can be used. We have tasks related to building source code and packaging in the Build tasks section. The task javadoc is used to generate Javadoc documentation, and is in the Documentation tasks section. The tasks for running tests and checking code quality are in the Verification tasks section. Finally, we have several rule-based tasks to build, upload, and clean artifacts or tasks in our Java project.
The tasks added by the Java plugin are the visible part of the newly added functionality to our project. But the plugin also adds a so-called convention object to our project.
A convention object has several properties and methods, which are used by the tasks of the plugin. These properties and methods are added to our project, and can be accessed like normal project properties and methods. So with the convention object, we can not only look at the properties used by the tasks in the plugin, but we can also change the value of the properties to reconfigure certain tasks.