The Gradle build tool for java

Introduction

Build tools are essential in software development because they automate the process of converting our source code into executable programs. The process involves compiling code, linking resources, executing tests, and deploying the product. Without build tools, developers would have to manually execute each of these steps, which can be time-consuming and prone to human error, especially in projects with many dependencies.

Gradle is one of the most powerful and flexible build tools. Its primarily used for Java projects but can also be applied to other programming languages such as C/C++ and Python. It’s designed to support complex workflows and provides a versatile way to define build logic. Unlike some other build tools, Gradle scripts are generally concise and human-readable. Gradle is also highly extensible, offering a rich API that enables developers to write custom plugins and tasks. Its incremental build capabilities save time by only running tasks that are necessary. As a result, Gradle has become a popular choice among many developers.

Dependency management with Gradle

Dependency management is a critical feature of Gradle that allows developers to automatically download and integrate libraries and other resources that their project depends upon. Many projects organize unrelated functionality into different parts of a modular system.

Gradle allows you to define different types of dependencies. Here’s an example of how you might declare dependencies in a build.gradle file, a script used in Gradle projects to define the project’s build configuration, including dependencies, plugins, tasks, and other build-related settings. We will only cover a few types dependencies, but keep in mind there are more!

dependencies {
    // Implementation dependencies are specific to a module and only used internally within the module
    // Define the dependency with group:name:version
    implementation 'org.apache.commons:commons-lang3:3.10'

    // Use the 'api' keyword for dependencies that should be made accessible to other modules
    api 'com.google.guava:guava:29.0-jre' 

    // Test dependencies are resources used exclusively for testing
    testImplementation 'junit:junit:4.13' 
}
repositories { 
    // Use Maven Central repository for most dependencies
    mavenCentral()    
}

During a build, Gradle finds and downloads each of the dependencies in a process called dependency resolution. It then stores resolved dependencies in a local cache called the dependency cache. Future builds use this cache to speed up the build process and avoid unnecessary network calls. This is yet another advantage of using build tools!

Gradle supports dynamic versions and classifier dependencies, which are useful for managing dependencies in a more nuanced way. For example, you can use a dynamic version like ‘4.+’ to always use the latest 4.x.x version of a library:

implementation 'com.somecompany:somelibrary:4.+'

In addition, Gradle provides the ability to exclude certain transitive dependencies - indirect dependency relationship between software components - that you don’t want to include, or to force a certain version of a library if there’s a conflict between different modules:

implementation('com.somecompany:somelibrary:1.2.3') {
    // Exclude certain dependencies
    exclude group: 'log4j', module: 'log4j'
}
// Apply configuration rules to all dependency configurations in the project
configurations.all {
    // In the case of a conflict, force a certain library version to be used
    resolutionStrategy.force 'org.apache.commons:commons-lang3:3.9'
}

Dependency Resolution in Gradle

You’re likely to encounter version conflicts between dependencies. Gradle offers multiple strategies to help handle them:

Consistent Versions with Platform Constraints

Gradle allows you to define a platform to enforce consistent versions of dependencies. A platform refers to a set of dependency versions for managing versions in order to maintain consistency and clean architecture. This is particularly useful in large multi-module projects. Here’s how you might use it:

dependencies {
    // Define your constraints under the dependencies block
    constraints {
        api('org.springframework:spring-framework-bom:5.2.7.RELEASE') {
            // Provide a reason for using this specific version
            because 'We want to align all Spring modules versions'
        }
    }
    implementation 'org.springframework:spring-core'
    implementation 'org.springframework:spring-context'
}

Custom Dependency Resolution Logic

Finally, heres a sneak peak of the more advanced things that you can do with Gradle. Sometimes, you may need to apply custom logic for dependency resolution. This capability is particularly beneficial in projects where standard dependency rules don’t align with project-specific requirements, such as managing version conflicts in complex multi-module projects, or when integrating with non-standard repositories. Gradle allows you to intercept and modify the dependency resolution process:

configurations.all {
    resolutionStrategy.eachDependency { DependencyResolveDetails details ->
        // Check if the current dependency is 'httpclient' from 'org.apache.httpcomponents'
        if (details.requested.group == 'org.apache.httpcomponents' && details.requested.name == 'httpclient') {
            // Force the use of a specific version of the 'httpclient' library
            details.useVersion '4.5.10'
            details.because 'Compatibility issues with newer versions'
        }
    }
}

Building a projects with many declared dependencies can be difficult to debug. In addition to the conflict resolution strategies listed above, Gradle has created tools to visualize and analyze a project’s dependency graph. You can use its Build Scan® tool to generate reports that tell you which dependencies failed to resolve. Read more about the Build Scan® tool here: https://scans.gradle.com/

Official documentation

Gradle official documentation: https://docs.gradle.org/current/userguide/userguide.html