Java Nullability Generation Using Gradle

A short project that exemplifies how you can generate java package-level nullability contracts using a Gradle task.

Package Level Nullability Contract

Following this StackOverflow thread: http://stackoverflow.com/questions/4963300/which-notnull-java-annotation-should-i-use we see that it is possible to set a default nullability value for java element types. The problem is that you get those nasty package-info.java files everywhere in the project.

Solution

To solve this, let's create a Gradle task that generates a separate folder tree to hold the package-info files outside the main source folders. The added benefit is that Gradle updates the files automatically when you add or remove a package to your project.

How to Configure

• The nullability annotation you can find here: \src\main\java\ro\stancalau\NotNullByDefault.java
• In the project root, find the package-info.template file
• In gradle.build there is a task named generatePackageInfo that is linked to the clean task
• In gradle.build, you need to set a variable named generatedPackageInfoDir which is the name of the generated folder. I suggest adding that folder to the VCS ignore file.
• To let the project take into account the generated sources, add the folder to sourceSets.main.java

Prerequisites

• Download and install Gradle
• Install JRE
• Ensure JAVA_HOME environment variable is set
• Ensure PATH environment variable contains path to Gradle
• Run gradle clean build in the project root to build the entire project

More information about this project can be found in this blog post