Dependency Management with Gradle

We're going to be doing a quick drive-by of a popular build automation tool called Gradle. Build tools are used to automate the process of packaging up and shipping your code to your users. When working with teams, it is essential to have a standardized build tool. We are, however, going to narrow our focus on managing dependencies.

When building software applications, often you use tools and libraries written by other developers. These software programs are your application's dependencies since your software (or development flow) depends on it. For example, you have used JUnit in Data Structures for writing unit tests. JUnit is an open-source program written to facilitate test-driven development in Java. JUnit is a dependency for most homework in the Data Structures course.

When a dependency that you are using requires another library, the required library becomes a transitive dependency. Essentially, what this means to you is that you also rely on that other dependency. As your project becomes larger and the code more complex, you will need a tool to manage all the dependencies. Enters Gradle! Now remember that Gradle is first and foremost, a build tool. It does also a great job of managing dependencies. Adding a dependency with Gradle is as easy as adding a line to your build script.

The easiest way to create a new project that is all Gradle ready is by using the IntelliJ Gradle template. Follow these instruction on "Getting Started with Gradle" to get a Gradle project up and running. If you have not already installed IntelliJ, please follow the instructions on "Install IntelliJ IDEA" and "Run IntelliJ IDEA for the first time."

Once done, open the build.gradle file in IntelliJ and find the following section:

dependencies {
    testCompile group: 'junit', name: 'junit', version: '4.12'
}

As you have guessed, that single line inside the dependencies block is all it takes to add JUnit to your project. When we later work with Javalin, for example, to build a RESTful API, we will add the following line to the build script:

compile 'io.javalin:javalin:3.7.0'

You might be wondering about the syntax¹ of Gradle and, for instance, what compile and testCompile mean. We will not cover these in OOSE; if you want to learn more about Gradle, please consult its documentation.

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1. Gradle is a domain-specific language, or DSL, that is based heavily on the Groovy programming language. Groovy is a dynamic scripting language that runs on the Java Virtual Machine. ↩